The Robber Fly is a unique and intriguing insect in the world of predators. With a large size and a stinger-like proboscis, it is often mistaken for other types of flies but holds its own spot in the category of predatory insects. Displaying various appearances and colors, it is an adaptable hunter that plays an important role as a natural pest control, feasting on insects like grasshoppers, moths, and other flies.
Robber Flies exhibit some fascinating characteristics, such as their strong, bristled legs which assist in capturing prey mid-air source. They have also developed impressive camouflage techniques, with some species mimicking bees or blending in with their surroundings to better ambush their prey. In fact, there are around 7,000 species of Robber Flies worldwide, and 1,000 native to North America, making them a widespread and diverse group of insects source.
While their fierce predatory behavior might seem menacing, Robber Flies are not harmful to humans. As generalist predators, their focus remains on other insects, making them beneficial to our ecosystem by controlling the populations of potential pests. So, next time you spot a Robber Fly, don’t be alarmed – they are simply doing their part to maintain balance in nature.
Overview of Robber Flies
Classification and Scientific Name
Robber flies belong to the family Asilidae and are classified under the order Diptera, class Insecta, phylum Arthropoda, and kingdom Animalia (source).
Robber flies exhibit various physical features including:
- Size: 0.2 – 2 inches
- Colors: Most are gray and black, some mimic other insects like bumble bees and wasps
- Bristles: Possess hairy or bristly bodies, and strong legs with bristles for prey capture
- Eyes: Large, widely-spaced compound eyes (source)
Habitat and Distribution
Robber flies are found all around the world. They are fierce predators, preying on a variety of insects like bees, wasps, dragonflies, spiders, beetles, and other flies. Specifically, there are about 7,000 species globally, with 1,000 native to North America (source).
Behavior and Biology
Prey and Predatory Tactics
Robber flies are predators known for their skillful hunting techniques. They primarily feed on:
- White grubs
Using their long, strong legs, they catch their prey mid-flight and inject venomous saliva to immobilize it before consuming it source.
Comparison of Robber Fly and Horse Fly:
|Feature||Robber Fly||Horse Fly|
|Legs||Long, strong||Short, sturdy|
Reproduction and Life Cycle
The life cycle of robber flies includes egg, larva, pupa, and adult stages. Female robber flies lay eggs in the soil or decaying organic matter source. The larvae are also predators, feeding on the eggs and larvae of other insects. After pupation, the adult robber flies emerge and continue their predatory behavior.
Beneficial Insects and Pest Management
Robber flies are considered beneficial insects due to their predatory nature. They play a vital role in controlling various agricultural pests. For instance, they help control populations of Hymenoptera like bees and wasps source. The University of Florida recognizes their importance in pest management and encourages the use of these natural predators to reduce the need for chemical insecticides source.
Size and Colors
Robber flies are medium-sized to large insects, with adult sizes ranging from 3 mm to over 50 mm in length1. They display varying colors, such as tan, black, brown, gray, and white2. These flies often have contrasting, patterned, or spotted markings on their body.
Wings and Legs
- Long, strong legs
- Bristled legs for prey capture
- Two wings for agile flight
Eyes and Face
Robber flies boast large, widely-spaced compound eyes, providing them with excellent vision for hunting5. Their face features a prominent proboscis, fashioned into a sharp tube or beak for injecting venom into their prey6. A comparison of Robber Fly features can be seen below:
|Size||3-50 mm in length|
|Colors||Tan, black, brown, gray, white|
|Wings||Two wings for agile flight|
|Legs||Spiny, bristled legs for capturing prey|
|Eyes||Large compound eyes|
|Face||Prominent proboscis for venom injection|
Robber Fly Relatives
Robber flies belong to the order Diptera, which includes many other types of flies. Some common relatives of robber flies are:
- Sand flies: Small, biting flies known for transmitting diseases
- Black flies: Tiny flies with a painful bite, commonly found near rivers and streams
- Horse flies & Deer flies: Large biting flies from the family Tabanidae, known for their painful bites
It’s important to note that robber flies do not have the same biting behavior towards humans as their relatives.
Wasps and Bees
Robber flies share some similarities with wasps and bees of the order Hymenoptera, such as:
- Predatory behavior: Just like many wasp species, robber flies are fierce insect predators
- Mimicry: Some robber fly species display hair and color patterns to resemble bees or wasps for protection
However, some key distinctions between robber flies and hymenopterans include:
|Robber flies||Wasps and Bees|
|Larval stage||Typically in soil||Ants, Bees: In nests, Wasps: In various habitats|
|Number of wings||2||4|
Ants, Larvae, and Lepidoptera
In the world of insects, robber flies (Asilidae family) also interact with ants and members of the Lepidoptera order, such as moths. They are known to prey on ants, as well as mature and larval forms of moths.
Some features of robber flies that can be helpful in distinguishing them from other insects like ants and Lepidoptera:
- Large, widely-spaced compound eyes
- A sharp, beak-like proboscis used for predation
- Two wings, instead of four like many other insects
The interaction between robber flies, ants, and moths exhibits the complexity and diversity of the insect world.
Impact on Humans and Environment
Biting and Stinging
Robber flies, despite their intimidating appearance, don’t usually bother humans. They are predatory insects that mainly target other insects, such as bees, wasps, and dragonflies1. That being said, they might bite when mishandled2. Their bite can be painful, but it’s not typically dangerous for people. To recognize a robber fly, look for these features:
- Narrow and tapering abdomen
- Large, widely-spaced compound eyes
- Prominent spikes on their legs
- Loud buzzing during flight
Role in Gardens and Ecosystem
Robber flies can actually be beneficial to gardens and ecosystems. They help keep populations of pest insects like aphids and other flies under control3. Additionally, they play a role in pollination, as they often visit flowers in search of prey. However, there are some drawbacks to their presence:
- Control pesky insects
- Contribute to pollination
- Indicate a healthy ecosystem
- Can potentially harm beneficial insects like bees
- Their bite can be painful if mishandled
Here’s a comparison table of robber flies and other flying insects:
|Insect||Body Shape||Flight Sound||Predatory||Bite Danger|
|Robber Fly||Narrow, tapering||Loud buzzing||Yes||Low|
|House Fly||Oval||Quiet buzzing||No||None|
|Horse Fly||Large, hefty||Loud buzzing||Yes||High|
|Honey Bee||Elongated||Soft buzzing||No||Low|
Robber flies lay their eggs in soil or plants4. Their larvae pupate and emerge as adult robber flies, continuing the cycle. By understanding their biology and ecological role, you can better appreciate and coexist with these fascinating, albeit intimidating, insects.
Over the years, our website, whatsthatbug.com has received hundreds of letters and some interesting images asking us about these insects. Scroll down to have a look at some of them.
Letter 1 – Robber Fly
on the screen door in Missouri
not the best picture, we’ve not seen one of these before. The stinger was huge! Any ideas?
This is a Robber Fly. They don’t have stingers, but they can bite. Eric Eaton wanted to point out that what appears to be a stinger is an ovipositor.
Letter 2 – Robber Fly Carnage
Subject: what kind of flying bug is this?
Location: massachusetts, USA
July 23, 2015 12:18 pm
it was flying around my room and had a very loud buzz.
This is a harmless, beneficial, predatory Robber Fly, and it will obviously buzz no more. In an effort to educate our readership on the harmlessness of most insects, we are tagging this posting as Unnecessary Carnage In the future, if you are able to trap an unwanted bug indoors in a glass, you can slip a postcard over the opening and relocate the critter outside.
Thank you for telling me what the bug was. I killed the insect because i saw the huge tail it had. It looked like a stinger that could do some damage. I don’t love killing anything, but i wasn’t going to take the chance to get a sting or a bite from a potentially poisonous insect.
I did read they can bite humans. They also have a toxic saliva that liquifies their prey.
Sometime i do catch the insects and let them outside. I wasnt going to take a chance with this unknown bug with a baby in the house though. Hopefully you understand.
Your explanation is fully understandable. What you mistook for a stinger is actually the ovipositor of the female, an organ used to lay eggs, and interestingly, in wasps, bees and some ants, the ovipositor has evolved into a stinger. We imagine the bite of a Robber Fly might have some unpleasant side effects, but we have never received a report of a person being bitten by one, nor have we heard of anyone who tried to handle a Robber Fly, which we imagine might result in a bite.
Letter 3 – Robber Fly from the Canary Islands
Subject: Flying insect
Location: Canarian island
September 17, 2016 4:05 am
I foundation this insect on my Windows in Gran Canaria
Thatcher insect is +/- 4cm long.
It is dangerous?
This is a Robber Fly, and here is a very similar looking individual posted to Getty Images. While a large Robber Fly might bite a person if it is carelessly handled, they are not aggressive towards humans, but they are predators that frequently hunt on the wing. Based on this Alamy image, your individual might be Promachus latitarsatus. The species is also pictured on Biodiversidad Virtual, and an image on Diptera Info shows a large Robber Fly eating a Dragonfly.
Letter 4 – Large Robber Fly from California
Subject: Camping with Insects
Location: Kennedy Meadows, CA
June 3, 2012 11:54 pm
When I was in Kennedy Meadows, CA I saw this huge fly looking insect. I think if may be a species of Robberfly, but i am not positive. I believe it was around last August when I saw it. Think you can help me out? Thanks a bunch!
Signature: Jared from California
This is indeed a Robber Fly. Our quick search this morning did not turn up a species match, but it reminds us of the genus Promachus pictured on BugGuide as well as the genus Proctacanthus also pictured on BugGuide. Both genera are also pictured on this wonderful Robber Fly website. Perhaps one of our readers will be able to assist with this identification.
Letter 5 – Bug of the Month January 2020: Giant Blue Robber Fly from Australia
Subject: Blue robber fly?
Geographic location of the bug: Mudgee, nsw
Time: 03:20 AM EDT
Your letter to the bugman: I saw anothe post with a very similar fly and you said it was an exciting find, so I thought I’d send you mine. Never seen one before, I assume it’s come to escape the fires.
How you want your letter signed: Cheers, Jeremy.
We always love posting excellent images of large Robber Flies, arguably among the most adept winged insect predators. We believe you are correct that this is a Giant Blue Robber Fly, Blepharotes spendidissimus, based on images posted online. The human finger for scale is a nice addition. We are well aware of the horrific fires currently burning in Australia.
Letter 6 – Large Australian Mystery Fly: Giant Yellow Robber Fly
Fly found in Australia
a friend of mine saw this fly and thinking of my entomology studies and insect collection he tried to catch it for me… he wasn’t sure what it was, and thinking that it may sting him, he hit it with a cloth and killed it (sigh). As you can see from the photo the thorax is very damaged but the rest of the body remains intact. I am stumped with it’s identification however as I believe it’s in the suborder Brachycera, Family Pantophthalmide. I have attached a photo and link of a Pantophthalmus sp. that I believe to be similar to this specimen. As far as I have found this family is located only in mid-to-south America (Peru, Brazil, Mexico, Panama, Costa Rico…) and am unable to research further as I can’t speak/read the language. Am I right in identification or way of the mark??? I am located in the mid-coast of the state New South Wales, Australia. It is generally a temperate climate where this specimen was found – not the neotropcial climate that the Pantophthalmide are said to reside. Any help would be greatly appreciated,
Pantophthalmus photo: http://www.diptera.info/photogallery.php?album_id=103
We need to bring in some big guns for this one. We are starting by correcting the spelling on the family in question and adding the missing “a” to Pantophthalmidae. We found a UC Riverside “Bug Spotlight” page on the family Pantophthalmidae that was written by Doug Yanega and we have contacted him to try to get his expert opinion. We will also contact Eric Eaton who frequently assists us in identifications. Meanwhile we are posting you image and waiting for our readership (yes that is you Grev) to comment.
Update: (01/06/2007) Large Australian Mystery Fly
Have a look at this site (especially the last photo) http://thebegavalley.org.au/1622.html What do you reckon?
It looks like you have nailed the identification to a large Robber Fly, Blepharotes coriarius. The website you located included the following information: “This is the only specimen I’ve seen. I’ve borrowed “Australian Insects” by Keith McKeown, from the library. Fortunately it has a good (black and white) water colour rendition of the fly and describes it thus: ‘The finest of all the Australian Asilidae. A very large black fly with the upper surface of its broad abdomen bright orange and tufted along the sides with patches of black and white hairs. The face is densely bearded. The wings are a rich smoky brown. It is rather a common insect in inland districts, especially in the Riverina, where it rests on fence posts and tree trunks in the hot sunshine. It flies away with a loud buzz when disturbed, often bearing away its impaled prey.’ “
Thanks so much for your help Daniel and Grev,
The photo with the “wings folded flat in line with the abdomen” makes it look exactly like a robber fly… I wonder if my specimen wasn’t so mangled if I would have recognized this? Well done guys! Cheers,
Letter 7 – Giant Robber Fly
What is this?
Location: Boulder, CO — Rocky Mountain foothills
June 30, 2011 10:38 pm
I ran across this insect while hiking in the hills around Boulder, CO. It’s about the size of my insect finger, and it flies as well. Otherwise, the picture should give you all the details you need.
This is one of the Giant Robber Flies in the genus Promachus. The species that are pictured on BugGuide all look quite similar and we do not feel confident taking the identification to the species level.
Letter 8 – Robber Fly
Flying insect in Texas
Location: Fort Worth, Texas
July 11, 2011 6:33 pm
Hi, I took this picture on my front porch in Ft Worth, Texas. It was about 4:30 in the afternoon on a very hot day in July.
It kinda looks like a dragonfly…but not quite. It is only about 1 1/2” long.
P.S. I also don’t live near any ponds or lakes. Very much an urban area.
Signature: Leah in Texas
This is a predatory Robber Fly, and we believe we may have identified it as Efferia aestuans, based on this photo posted to BugGuide.
Thank you! The end of it’s tail was really throwing me.
Letter 9 – Giant Blue Robber Fly from Australia, we believe
Subject: Black fly/cicada thing?
Location: Newcastle, NSW, Australia
December 5, 2015 12:28 am
Dear Mr. Bugman, I live in Newcastle NSW Australia where summer is just kicking off and I recently stumbled upon this demonic looking critter. It was first hanging off a leaf in my garden where I noticed it had a dark blue shine on its back. It’s eyes were a little apart and it had lots of tiny hairs around it’s snout? There was also a jagged edged plate looking thing beneath its belly. After hours of browsing I’m still not totally convinced it’s a female horsefly despite it being the most similar description I could find. If you could confirm what this creature actually is for me it would be much appreciated, it looks like such a fascinating creature. Thanks
This is a very exciting submission for us. Though Cicadas are frequently mistaken for flies, and though Australia does have a great diversity of Cicadas with creative common names, this is a True Fly, though not a Horse Fly. We are relatively certain it is a Giant Blue Robber Fly, Blepharotes spendidissimus, and though we are not 100% certain of the species, we are confident that the genus is correct. We do not believe this is the closely related and even larger Giant Yellow Robber Fly. The Brisbane Insect site has nice images of the Giant Blue Robber Fly and there are not many other images found online. The individual pictured on Oz Animals appears to be a male, and we are relatively certain your individual is a female. We believe this other individual from New South Wales that is in our archives is most probably Blepharotes spendidissimus as well.
Letter 10 – Bee Hunter
Any idea what this is, I live on Vancouver Island, Canada, and have seen a number of these insects attacking and killing wasps and bees. Any info would be appreciated.
You have a totally awesome photograph of a Robber Fly, Family Asilidae. There is one genus, Laphria, known as Bee Hunters. Your fly belongs to that genus. Adults feed on Honey Bees, though your photo shows a Yellow Jacket being devoured. A species in California and Oregon is Sacken’s Bee Hunter, Laphria sackeni. Also, the larvae of robber flies are pretty much now assumed to be parasitic on beetle grubs. According to our Audubon Field Guide: “Sacken’s Bee Hunter flies rapidly and suddenly descends on an unsuspecting bee. It seizes its victim on the thorax so the bee cannot use its stinger.” You might want to submit your photo to the new field guide we advertise at the top of our homepage.
Letter 11 – Robber Fly, We believe
Subject: Monster Robberfly?
Geographic location of the bug: Jones Hole Creek Northeast Utah, near Colorado border
Time: 02:19 PM EDT
Your letter to the bugman: Found this big guy on a hiking trail with my family in north eastern Utah. Kind of looks a bit like like a Robber Fly, but it’s HUGE!
How you want your letter signed : Steven Erickson & Family
We agree that this does resemble a Robber Fly, and being huge is not an exclusionary trait for the family as there are many very large Robber Flies, including the Bezebul Bee Eater, and though the linked image from our archives is not critically sharp, the size of the Red Wasp prey should give you some sense of scale. We were not successful in finding a matching image on BugGuide, which might indicate it is a rarely encountered species due to the remote location, or perhaps it is not a Robber Fly. What we can say with some degree of certainty is that this individual is female because of the space between the eyes and that is blends perfectly with the color of the sand indicating it had adapted well to the environment. We did some additional research on BugGuide on other families in the superfamily to which the Robber Flies belong, Asiloidea, and we feel there are some Flower Loving Flies in the family Apioceridae that look quite similar, but not exactly alike, including this unidentified individual on BugGuide and this member of the genus Apiocera on BugGuide. Our editorial staff is currently out of the office on holiday, but next week when we return, we will consult with Eric Eaton to get his opinion. If we are correct that this is a Flower Loving Fly in the family Apioceridae, then this will be a new category for our archives. Also, in an effort to provide accuracy in the location, we surmise that you mean Jones Hole Creek and not Joned Hole Creek.
Update: We just posted this image of a Stinkfliege in the family Xylophagidae and we can’t help but to entertain the possibility that this Fly might also be a member of that family.
Update: June 16, 2018
After further pondering and a comment from Cesar Crash, we agree that this is most likely a species of Robber Fly.
Letter 12 – Robber Fly, NOT Syrphid Fly
Subject: Tiny, graceful, and apparently not a fairyfly
Location: southern California
October 25, 2013 9:19 pm
Hi again! I’ve written in a few times, and am very grateful for the identifications. I found this little flying beauty on one of my bug walks in southern California today (October 25). It is in a garden; there is a stream nearby, but not immediately proximate to this plant. The insect is about the size of a mosquito. With its long, delicate abdomen, it looked like a fairy to me when it was in flight, but as far as I can tell the term ”fairyfly” is applied to a totally different kind of insect. After spending some time unsure of where to even begin in identifying this lovely creature, I’m conceding defeat. Can you help me?
We really wish your photo revealed some individual features of this unusual insect. The head and eyes look like those of a Fly in the order Diptera, and the body most closely resembles that of a wasp in the order Hymenoptera. The fly family Syrphidae contains many individuals that mimic stinging Hymenopterans, so that is our best guess. We were unable to find any matching images on BugGuide, but we did locate two that are somewhat similar, including Baccha elongata and Pseudodoros clavatus. Though they look somewhat similar, we are quite certain neither of those is your species. The hind legs on your individual are very distinctive, which should aid in the correct identification. We are going to contact Eric Eaton for assistance.
Update: Bee Fly is Another Possibility
We are now entertaining the possibility that this might be a Bee Fly in the family Bombyliidae as there is a similarity to the genus Systropus that is pictured on BugGuide.
Correction Courtesy of Eric Eaton
This is actually a robber fly in the subfamily Leptogastrinae. Most of the genera have this skinny appearance.
Thanks very much to you and Eric! I had actually briefly entertained the idea of a robber fly because of the way it was hanging, but I just thought it was much too small so I didn’t look closer at that idea. That’s great to know.
Letter 13 – Bee-Like Robber Fly
Subject: Flying insect
Location: Benndale Mississippi
April 13, 2017 4:51 pm
I thought this was a hornet. Not sure.
Signature: Kathy cates
We have identified your Bee-Like Robber Fly as Laphria saffrana thanks to images on BugGuide, and according to BugGuide: “considered to be a mimic of the southern yellowjacket (Vespula squamosa) queen.”
Letter 14 – Bee-Like Robber Fly from Vancouver Island
Subject: Robber fly?
Location: Lat. 48.372 Long. 123.538
June 24, 2017 9:14 am
Thank you again for this great site!
Here’s a guy my Dad caught in the house yesterday. At first we thought it was a bumble bee, but your site helped me determine that it is likely a fly.
Would you kindly check these photos out, please.
We let it go. It seemed fine after its stay in the glass for inspection! We are still at Lat. 48.372 Long. 123.538, southern Vancouver Island, Metchosin, William Head Road.
Thank you so much for your help!!!!
Signature: Sue Hughes
Your images of a Bee-Like Robber Fly in the genus Laphria are spectacular, and we are especially excited that they nicely reveal the red-tipped abdomen. Bee-Like Robber Flies are predators and these larger Robber Flies prey upon stinging insects like bees and wasps. It is believed they mimic their prey, both for protection from other predators who might be off put by the thought of trying to eat a stinging insect, and because they are able to more closely approach prey before alarming a potential meal. This species seems to have adapted to mimic your locally common red-tailed Tri-Colored Bumble Bee which according to BugGuide should not be called a Red Tailed Bumble Bee because: “Red-tailed Bumble Bee (not recommended, as it also refers to Bombus lapidarius, a Eurasian species).” We believe we have correctly identified your Robber Fly as Laphria asturina on BugGuide, but alas, it has no common name. You might consider posting your images to BugGuide as they only have two examples, and we do believe your images are better for identification purposes. We also located an image of a living individual and its meal on PICSSR (warning: adult ad content on this link).
Thank you very much for help with our latest bug adventure!
I will send the images to BugGuide on your say-so, if I can figure out how to do it.
You have made our day!!
Letter 15 – Bee-Like Robber Fly
Subject: Wasp/Bee/Strange Specimen?
Geographic location of the bug: Tumwater, Washington, near the Deschutes River
Time: 01:12 PM EDT
Your letter to the bugman: I caught this aggressive little guy alone when he landed on a plant near a riverbank in Tumwater, Washington – near Olympia. After hours of entomological research I cannot for the life of me find something with a thorax like this, but “furry”.
How you want your letter signed: out-of-options
Your identification research did not prove successful because, though it resembles a stinging insect, this is not a Bee nor a Wasp in the order Hymenoptera, but rather a predatory Robber Fly in the order Diptera and the family Asilidae. It sure looks to us like it might be the Bee-like Robber Fly Laphria columbica which is pictured on BugGuide and reported from Washington.
Letter 16 – Bee-Like Robber Fly
Subject: Be? Fly?
Geographic location of the bug: Oroville California
Time: 08:36 PM EDT
Your letter to the bugman: What is this insect? Bug? I found this on my bush today.
How you want your letter signed: Sharry
This is a Bee-Like Robber Fly in the genus Laphria, and there are two similar looking species found in California. We believe you encountered Laphria sackeni which is pictured on BugGuide and which flies from April to July, though we would not rule out that it might be the similar looking Laphria astur, which is also pictured on BugGuide and which has a similar flight season.
Robber Flies are predators in the family Asilidae, and according to BugGuide, they are also known as Assassin Flies, which might be a more appropriate common name. Both common names probably arise from their stealth hunting tactics. The etymological origin of the name Robber Fly is uncertain, however, they are not really robbing anything except perhaps robbing its prey of life. According to Galveston County Master Gardeners site: “Robber flies are among the few insects that catch their prey in mid-flight. An individual establishes a perch zone. From there, it swoops out to snatch the unsuspecting victim that is often larger than its aggressor and may even include spiders, large predatory insects, and, sometimes, other robber flies.”
Letter 17 – Bee-Like Robber Fly
Subject: Bee-like Robber Fly
Geographic location of the bug: Mid-Michigan
Time: 09:05 AM EDT
Your letter to the bugman: I loved your recent post of a bee-like Robber Fly preying on a Sawyer Beetle, which I have shared on social media. Here is a pic of a very friendly Robber Fly that’s been hanging around our deck the past week. At first I thought it was a deformed bumblebee until I got the attached photo and noticed the eyes, legs, and especially that wicked looking mouthparts was different than a bee. This insect often perches on us or on our furniture, although I’m a bit concerned of accidentally placing a hand down on top of him.
How you want your letter signed: Mike
Thanks for your kind words. We believe your Bee-Like Robber Fly might also be Laphria thoracica because of the abdominal markings and the dark hairs on the face. Your image is stunningly beautiful with exceptional detail, especially the wing veinage.
Letter 18 – Bee-Like Robber Fly
Subject: Bug spotted while camping
Geographic location of the bug: Naked Falls on the Washougal river
Time: 11:53 AM EDT
Your letter to the bugman: Hi, when this bug landed on my bag I was intrigued. Growing up here I have never seen one like it and google image search is not giving me any results. Just curious about it if you have the time. Thanks!
How you want your letter signed: Loni Lane
We believe we have correctly identified this impressive, predatory Robber Fly as Laphria columbica, one of the Bee-Like Robber Flies based on BugGuide images.
Letter 19 – Bee-Like Robber Fly
Subject: Is this a wasp?
Geographic location of the bug: Vancouver area, British Columbia, Canada
Time: 09:49 PM EDT
Your letter to the bugman: I came across this aggressive little monster outside in late August near Vancouver. He was easily 2x the size of a honeybee, and while he preferred hanging out on the wooden bench, he made several short (1-2 second) flights before finding a new landing spot each time on the bench. He even had a mid-air tumble with a flying insect who dared to pass near him. He seemed quite aggressive and unpredictable, so sorry for the blurry pic! I couldn’t get too close.
How you want your letter signed: Agatha
This is a Robber Fly, not a Wasp, and it appears to be Laphria astur, based on this BugGuide image. Large Robber Flies are aerial predators that take prey on the wing, and the “mid-air tumble” you witnessed might have been a failed attempt to capture a meal.
Letter 20 – Giant Robber Fly
large fly looking dead insect.
Fri, Dec 19, 2008 at 4:39 PM
We found this one ( dead already ) on the ground along the grand canyon, az. It was at least 3 inches long and had these striking stripes on its back end and these large eyeballs! the kids thought this was so neat looking and because of its size it was a bit shocking that it was dead.
anyhoo – I have been trying to identify it and have had no luck. can anyone help?
thanks so much!
claudia and kids ( thomas hannah emma and lilly)
grand canyon arizona
Hi Claudia and Kids,
Now that the semester is finally finished and we have submitted our grades, we are trying to send Christmas cards to friends and family. WE have been neglecting our web site email and have only been posting one or two letters a day. We are happy to inform you that this is a predatory Robber Fly, probably a Giant Robber Fly in the genus Promachus. We believe it may be Promachus sackeni which is found in Arizona according to BugGuide, but we would like to have an expert opinion to substantiate this identification.
Letter 21 – Giant Robber Fly from Australia
Big Bee / Wasp?
Location: Kalgoorlie Western Australia (Desert)
January 30, 2011 1:18 am
can u identify this thing? It was fouund at my hsbands work yesterday (Gold mine, Kalgoorlie Western Australia) after it stung / bit him, mild irritation went away quickly. I have tried to identify it withot success.
Signature: Sarah Ryan
This is a Robber Fly in the family Asilidae. Robber Flies are predators, and though they do not prey upon humans, they can bite if carelessly handled. We searched the Insects of Brisbane website and we believe we have identified your specimen as a Giant Robber Fly, Phellus olgae.
Letter 22 – Giant Robber Fly from Idaho
Weird bug in Idaho
Location: Lake Coeur d’Alene, Idaho
August 20, 2011 2:49 am
I shot this picture August 17th at Lake Coeur d’Alene, Idaho, in the late afternoon. Any help would be appreciated! Thank you!
Signature: Kelly, Everett, WA
This magnificent predator is a Giant Robber Fly, and Robber Flies just might get the prize for the most adroit insect predators who hunt on the wing. Large Robber Flies can kill large Dragonflies. The closest match we could find on BugGuide at the start of our research was for Proctacanthus heros, though to the best of our knowledge, that is a southern species. The red legs and red abdomen look very similar to your individual. We suspected it was the same genus, however, there are no other matching images that we could find on BugGuide. We did locate this marvelous Random Natural Acts web page titled Proctacanthids devoted to the genus. At last we discovered this photo of Stenopogon inquinatus from British Columbia on BugGuide that looks like a very close visual match to your individual, and we believe that is a correct species identification. Random Natural Acts also has a Stenopogon page.
Letter 23 – Giant Robber Fly
Subject: Large fluffy faced fly laying eggs in old board
Location: Colorado City, Colorado
June 5, 2015 11:49 am
What kind of bug is this little lady? She is about an inch long and I believe she was laying eggs while I was snapping these photos. This was taken in my backyard on June 5th, 2015
This is a female Robber Fly, and we found a very similar looking individual on the Bandelier National Monument website, but alas, it is not identified to the species level. Eric Eaton has an image of Promachus albifacies from Colorado Springs that looks very similar, and researching that on BugGuide, we believe that at least the genus with members known as Giant Robber Flies is correct. We are going to be out of the office later in June, so we are postdating your submission to go live during our absence.
Letter 24 – Giant Robber Fly
Subject: Alien insect
Location: Olathe, KS
August 13, 2017 1:15 pm
This creature was spotted on the deck of a home in Olathe, KS. I’ve never seen anything like it. Any idea what it is?
Signature: Chris N.
This is a predatory Giant Robber Fly in the genus Promachus, but we are unable to provide a definitive species name at this time. It is possible that it is Promachus vertebratus which is described on BugGuide as “Green eyes, sometimes with some red” and it is reported from Kansas. Of the genus BugGuide notes: “Large robber flies with tiger-stripe pattern on abdomen” and “prey: insects, often Hymenoptera” leading to the common name Bee Killer.
Letter 25 – Giant Robber Fly
Subject: Impressive killer
Location: Roswell, Georgia
August 22, 2017 1:54 pm
I saw this flying around our yard yesterday, and dead in our driveway today. I believe it is the red-footed cannibal fly you mention on your page 3 of horse flies. Can you confirm this for me?
Signature: Maggie Bean
Dear Maggie Bean,
This is definitely a Giant Robber Fly in the genus Promachus, but since its “feet” are hidden under its body, we cannot say for certain that it is a Red Footed Cannibalfly, but it is in the same genus which is well represented on BugGuide by many similar looking species.
Letter 26 – Giant Robber Fly
Subject: Bee Identification
Geographic location of the bug: Spruce Pine NC
Time: 04:28 PM EDT
Hi I saw this little critter on its back and was going to help flip him over but he turned back without my help. I thought he was just a regular Bee until I saw his wings legs and stinger. It’s the beginning of fall here I have to say I’ve never saw a bee quite like this!
How you want your letter signed: SJ
This is not a bee. It is a predatory Giant Robber Fly in the genus Promachus, but we are not certain of the species. What you have mistaken for a stinger is the ovipositor the female uses to lay eggs. Here is a similar looking individual on BugGuide.
Letter 27 – Giant Robber Fly
Geographic location of the bug: Los Angeles backyard
Time: 11:36 AM EDT
Hi! My grandson found this black bug–it’s about 1 1/2 ” long with a torpedo-shaped body with a narrow pointed end. The bug often elevated its rear end. He first found it on it’s back and saw it arch it’s back and move it’s legs over its body to flip onto it’s stomach. Not sure how many wings it has.
How you want your letter signed: Brody
We believe this large predator is a Giant Robber Fly in the genus Promachus, probably Promachus albifacies based on this BugGuide image. It also resembles this unidentified species on the Natural History of Orange County site.
Thank you so much for your response! My grandson (11) is thrilled to know the insect name and be on your terrific site.
Letter 28 – Giant Robber Fly
Subject: Cross between a wasp and dragonfly
Geographic location of the bug: Maryland
Time: 12:02 AM EDT
Any ideas? Some are calling this a cicada killer but those look MUCH more like wasps…this has a more dragonfly like tail but appears to only have two wings..
How you want your letter signed —
Chris in Md
This is a predatory Robber Fly, and you were astute to observe that it has a single pair of wings. We believe it is a Giant Robber Fly in the genus Promachus which is well represented on BugGuide.
Letter 29 – Red Footed Cannibalflies
Subject: robber fly identification
Geographic location of the bug: New Jersey
Time: 01:18 PM EDT
Your letter to the bugman: Greetings:
I’m having trouble identifying Robber Flies. I’ve uploaded 2 fairly similar pictures (more pictures can be found at https://www.inaturalist.org/
P.S. I think Robber Flies are interesting, but don’t really know much about them except that they’re considered fairly tough predators in the arthropod world.
How you want your letter signed: Baffled By Robberflies
Sometimes it is not possible to identify a species conclusively from a photograph alone, and the Giant Robber Flies in the genus Promachus can be a challenge. We are somewhat inclined to doubt the accuracy of the individual identified as Promachus hinei on iNaturalist because BugGuide lists the range of the species as being considerably west of New Jersey with Ohio being the easternmost sighting. Because of the proximity of your two sightings in both location and time, we would be most inclined to suppose them to be the same species, and the Red Footed Cannibalfly is a likely possibility, especially since both of your individuals have red “feet” and the physical description on Encyclopedia of Life states: “Adults are 28 – 35 mm long. Typical of robberflies, the eyes are large and separated by a deep trough on top of the head. The body is covered in yellow bristles, particularly on the head and abdomen. The legs are black, except for orange tibia and pulvilli. As with other members of the genus Promachus, this species has sharp claws and an abdomen that extends beyond their folded wings. ” We apologize for not being able to provide a conclusive identification and we suspect that if actual specimens were to be identified by a dipterist specializing in Robber Flies, many of the individuals identified on our site as Red Footed Cannibalflies might actually be members of a similar looking species in the same genus. Like many other large Robber Flies, Red Footed Cannibalflies and other members of the genus are able to take large prey, often stinging wasps and bees, on the wing. Thank you for becoming a Patreon member and helping to support the free service we are able to supply on the World Wide Web.
Thanks for telling me what you know about these guys. I suspect that I’m going to have this problem with a lot of insects; too many similar-looking relatives. (I was kind of hoping you’d be able to tell me that no other species that looks like the Red-footed Cannibalfly lives in NJ.)
We located this comment on BugGuide “As I understand it, there are three ‘tiger-striped’ species of Promachus in the eastern U.S., with P. hinei being the most common in the central U.S. It is distinguished from the more southern P. rufipes by the reddish rather than black femora and from the more northern P. vertebratus by the larger dark areas dorsally on the abdominal segments and distinctly contrasting two-toned legs.” That supports our supposition that both of your individuals are Red Footed Cannibalflies, Promachus rufipes.
That was helpful. Just for due diligence, I then checked out BugGuide’s info on Promachus vertebratus to see if that could be a good candidate for my Robber Flies. And it really isn’t; P. vertebratus’s range is typically outside NJ, and it’s green or red eyes aren’t a match for any of my Robber Flies.
I’m cautiously optimistic that the Red-footed Cannibalfly is what I’m seeing.
And we agree, so we are changing the subject line of the posting to reflect that.
Letter 30 – Giant Robber Fly: Promachus bastardii
Subject: What’s this insect?
Geographic location of the bug: Houston Texas
Time: 12:34 AM EDT
Your letter to the bugman: We have been searching all night to identify this bug. Please help us!
How you want your letter signed: Drema from Houston
We believe we have correctly identified this Giant Robber Fly with its distinctive white-tipped abdomen as a male Promachus bastardii thanks to this BugGuide image. According to BugGuide: “Males have distinctive white tip on abdomen and white bands on thorax.”
Letter 31 – Giant Robber Fly
Subject: Possible Hymenoptera?
Geographic location of the bug: Greene county, MO
Time: 07:03 PM EDT
Your letter to the bugman: My mom sent these pictures and I’m not sure what it is.
How you want your letter signed: Jenny Parsons
This is a Giant Robber Fly in the genus Promachus, possibly a Red Footed Cannibalfly, not a Hymenopteran. Giant Robber Flies prey on large flying insects, frequently eating wasps and bees.
Letter 32 – Large Robber Fly: Saropogon dispar
Subject: Hairy wasp-like bug with some kind of oral stinger
Geographic location of the bug: Southeast Texas, USA
Time: 10:51 AM EDT
Your letter to the bugman: I’ve been seeing these guys at my work which is a fracking site in the middle of a cattle ranch. I have seen about 5 of them but all separately, not in a group. They look like giant wasps, but they’re very hairy and have some kind of stinger out of their mouths. I may have seen a stinger out of the thorax as well but I’m not sure. And I have noticed multiple dead bug carcasses around the area, such as grasshoppers and beetles. I thought it might be relevant in case these bugs are like the wasps who lay parasitic eggs in paralyzed bugs.
Picture taken in July.
How you want your letter signed: Dave
This is a predatory Robber Fly, and Robber Flies frequently capture large flying insects that they feed upon, so the carcasses you have found might have been prey. Like other Flies, Robber Flies do not chew prey. They feed on the fluids, leaving a dried carcass behind. We are having trouble matching your images to an exact species or even a genus. Its most obvious diagnostic features are its long legs, white beard, black wings and striped abdomen. It really resembles a Hanging Thief in the genus Diogmites, but they are usually orange. We did locate a dark Hanging Thief on BugGuide, Diogmites platypterus, and it has a white beard and black wings, but your individual lacks the orange legs. Our best guess at this time is the enormous Microstylum morosum, pictured on BugGuide, but they don’t have white stripes on the abdomen. Does your individual have green eyes? That is difficult to discern in your images. Prolepsis tristis pictured on BugGuide also looks similar, but lacks the diagnostic white beard. We have written to Eric Eaton for assistance. For now, we are certain this is a predatory Robber Fly in the family Asilidae, and we hope to have a more specific identification for you soon. Perhaps our readers will be able to assist.
Thanks for the response! Yes the eyes were a dark green color. And it was very large, I approximate it to be 1.5-2 inches long. The Microstylum morosum looks like the closest match to me except for that abdomen and the bright green eyes. I didn’t know anything like this family of insects existed!
If it is indeed Microstylum morosum, it is the largest Robber Fly in North America.
Eric Eaton Responds
Ok, I submitted to the Facebook group, but then looked at the website for robber flies of Arkansas and may have found it: Saropogon dispar: http://www.hr-rna.com/RNA/Main%20pages/Diogmites%20frame%20page.htm
author, Kaufman Field Guide to Insects of North America
Thanks so much Eric. We looked it up on BugGuide and Saropogon dispar sure does look correct.
Letter 33 – Giant Robber Fly
Subject: Never seen this before HELP!!!!
Geographic location of the bug: East TN
Time: 12:31 AM EDT
Your letter to the bugman: Hey Bugman,
I was at work when this fellow showed up nobody knows what it is. I was a little freaked out (ok a lot). Looks like some sort of crazy bee.
How you want your letter signed: Christina
This is a Giant Robber Fly in the genus Promachus, a predatory species that often catches large winger prey.
Letter 34 – Giant Robber Fly
Subject: Robber fly type
Geographic location of the bug: monmouth county, new jersey
Time: 04:09 PM EDT
Your letter to the bugman: hey i am looking through archived photos and i would love more specific input on this robber fly. is it possible to id genus/species from this photo. taken mid june 2016. at the time i thought hanging thief but that’s as far as i got. thanks in advance!
How you want your letter signed: WS
Letter 35 – Giant Robber Fly
Subject: robber fly id
Geographic location of the bug: barnegat new jersey
Time: 08:26 PM EDT
Your letter to the bugman: giant robber fly – asilidae family. but what genus species? promachus?? seent at cloverdale farm county park 7/28/18. i always have robber fly questions, any resources for field guides or at least to narrow down genera in nj?
How you want your letter signed: WS
We believe you are correct that this is a Giant Robber Fly in the genus Promachus, and it looks most like Promachus hinei based on this BugGuide image, but that species is only reported as far east as Ohio on BugGuide. It might be the same species as your previous submission. You can try submitting your images to BugGuide to see if the network of contributors there can provide you with a species identity.
Letter 36 – Giant Blue Robber Fly from Australia
Subject: I think it is under the order Mecoptera
Geographic location of the bug: Sydney Australia
Time: 07:07 PM EDT
Your letter to the bugman: Hello,
I live in Sydney Australia and it is currently late spring.
I spotted this insect on my balcony and think it is under the order Mecoptera. I tried to catch it to give to donate to the entomology department at the University of Sydney because I know they don’t have many.
I am very interested in knowing what type of insect it is because I spent 3 months catching insect for my entomology major work and just handed it in. Shame I didn’t find one 3 week earlier!
Thank you for your time.
How you want your letter signed: Ethan
This is definitely NOT a Scorpionfly in the order Mecoptera. It is a True Fly in the order Diptera, and we believe it is a Robber Fly in the family Asilidae. We believe it might be a Giant Blue Robber Fly, Blepharotes spendidissimus, which is pictured on Brisbane Insects where it states: “The Giant Blue Robber Fly has the relatively small head, legs are not long but with board abdomen. The body and legs is covered with short grey hairs. Whole body, includes eyes, abdomen and legs are in dark steel blue colour. Pair of Wings are tinted in steel blue as well. “
Letter 37 – Giant Blue Robber Fly from Australia
Subject: Is this a giant blue robber fly?
Geographic location of the bug: Dapto NSW
Time: 11:56 PM EDT
Your letter to the bugman: We found this in our backyard….what is it?
How you want your letter signed: Gwen age 8
We apologize for the delay in our response. Daniel was out of the office for over a week spending the Thanksgiving holiday with his 90 year old mother and he did not answer any mail. We agree that this is most likely a Giant Blue Robber Fly, Blepharotes spendidissimus, which is one impressive predator. Your images are awesome. Can you provide us with any observation details from the sighting?
It stayed in the same position for days- we thought it was dead!! Then just disappeared! Was amazing to look at though!
Letter 38 – Large Robber Fly from Montana
Subject: What’s this bug?
Geographic location of the bug: Polson, Montana
Time: 09:22 PM EDT
Your letter to the bugman: Hello-
We spotted this bug on the deck railing today. Can you enlighten us as to what it is? We are near Flathead Lake & some stagnant ponds. We’ve never seen anything like it. Thanks!
How you want your letter signed: Suzanne M
Thank you so much! I read up on the Stenopogon & found that it can be a predator of hummingbirds. This one was hanging out on the railing, right by the hummingbird feeder. Next time we see it, we’ll definitely shoo it away.
I really appreciate your fast response! Cheers!
Letter 39 – Large Robber Fly: Microstylum morosum
Subject: Flying insect
Geographic location of the bug: Irving tx
Time: 05:09 PM EDT
Your letter to the bugman: I thought this was a wasp chasing me in the flower bed. He buzzed loudly.
How you want your letter signed: Peggy clark
Letter 40 – Giant Robber Fly
Subject: Kind of bug
Geographic location of the bug: North Carolina
Time: 07:23 PM EDT
Your letter to the bugman: Judy curious what this id
How you want your letter signed: Thank tip
This is a Giant Robber Fly in the genus Promachus. You may read about the group on BugGuide where it states: “Large robber flies with tiger-stripe pattern on abdomen.” It might be a Red Footed Cannibalfly, though your individual appears to have fewer stripes on the abdomen.
Letter 41 – Robber Fly from Elyria Canyon Park
Subject: Robber Fly from Elyria Canyon Park
Location: Elyria Canyon Park, Mount Washington, Los Angeles, CA
April 15, 2013
Yesterday while volunteering in Elyria Canyon Park, I noticed this fly in the tall grass that we were removing as part of brush clearance in the butterfly garden. I thought it was a Soldier Fly and I asked Becky to take a photo. I couldn’t find a matching Soldier Fly on BugGuide, so I requested assistance from Eric Eaton. He quickly responded.
Eric Eaton provides an identification
It is a robber fly. Looks to me like maybe Dioctria for genus, but no Bugguide records from there, so….?
Letter 42 – Robber Fly
Subject: Is this a robber fly
Location: Princeton NJ
July 30, 2017 4:37 pm
I have never seen a fly like this. It’s about an inch long. I tried to find it on the Web, but the closest thing I could find is a robber bug. Is that what it is?
Thanks to this BugGuide image, we are confident your Robber Fly is a male Efferia aestuans. According to BugGuide: “The most likely robber fly to land on humans. (comment by Herschel Raney) Sometimes fearless. The males are much less common and harder to approach. (comment by Herschel Raney) The commonest species of Asilinae in the northeast (comment by Herschel Raney).”
Thank you Daniel. Are these beneficial insects, are should I kill these when I see them. I accidentally squirted it with the hose, and it just sat there looking at me. With insects, I try to identify them if they are new to me. I’m an organic gardener, and I rely on benefical insects.
Hi again Barbara,
Robber Flies are beneficial predators. While they might bite a person if carelessly handled, they are not aggressive. We do not condone killing Robber Flies.
Thank you! If I ever see it again, I will let it be. We have honey bees, but we can spare a few. We also have hummingbirds and hummingbird moths. Hopefully the robber fly will not bother those.
Thanks again. I really appreciate your service.
We believe your hummingbirds and moths will be safe as they are probably too large for this species, however we do understand that large Robber Flies can attack hummingbirds, something you can read about on Hilton Pond.
Letter 43 – Robberfly feasting on Fly
I just discovered your site, When I took this picture last month I thought it was a mother doting over a dead relative. Now I think it’s a robberfly eating it’s victim? This insect wither was there for a couple of days, and didn’t mind my getting to within 2 inches with a macro lens.
The only insects that exhibit anything remotely resembling doting are the social insects in the order Hymenoptera, the Ants, Bees and Wasp, and Termites in the order Isoptera. Robberflies are dispassionate about their meals.
Letter 44 – Robberfly Feasts on a Relative
Baby Red-Footed Cannibalflies!
Location: Northern Kentucky, near Cincinnati, OH
August 17, 2010 7:56 pm
My garden has been hosting a red-footed cannibalfly this year that I’ve named ’Angel’ because she was ’bug of the month’ for August which pretty much makes her a ’Centerfold’ in bug land. 🙂
I scan my garden for her and am usually rewarded with at least a glimpse of her every day.
Last Sunday, I spied a familiar profile, in miniature, on one of my wild phlox. A baby Angel!
Like its mother, it didn’t seem to mind my snapping camera. It was only about 1/2” long. I saw two others before the day was through.
The next day, I caught sight of one of them again and I was amazed at how much it had grown in a single day. It was feeding on what I believe to be a fly, but could be a small bee. It deftly caught prey suitable to its own diminutive size.
Amazing little predators.
(p.s. Please feel free to edit my content as you see fit.)
Hi Again Ragdoll,
There is absolutely nothing to edit from your entertaining and delightful letter, but we would like to take the opportunity to make some corrections. Your most recent Robber Fly is not a Red Footed Cannibalfly and we doubt we have the necessary skills to identify which of the 883 North American species indicated by BugGuide that it might be. You also have a significant conceptual error in your letter that we would like to explain. Insects undergo metamorphosis and they do not “grow” the way creatures without an exoskeleton grow. The exoskeleton of an insect is rigid, and before an insect can increase in size, it must molt or shed its hard outer skin. Insect nymphs and larvae grow after molting, but adults do not since they have reached the end of their metamorphosis. A “baby Angel” would not have wings. Instead it would be a wormlike larva. Many fly larvae are known as maggots. Your “baby Angel” is actually an adult of a distinct species. The prey in your two food chain images appears to be a fly as well.
WOW! Thanks for the spanking, Bugman! It’s totally humbling to be wrong so many times in a single letter. 😉
I honestly appreciate all the corrections. The thing that’s weird is that the ‘tiny’ robber fly looks like it has the red legs, like Angel. All of a sudden, three of them appeared on the same day. The next day, I saw another, but it was a little larger and looked a little different. That’s the one with the fly.
The oddest thing of all, though, is that I have never seen a robber fly in my life till this year. I know that doesn’t mean they weren’t there, but I’ve always been pretty observant about the ‘wildlife’ in my gardens. Maybe it’s like when you learn a new word. You seem to hear it everywhere for awhile.
I find all your info fascinating and I appreciate the education. I’ve always loved to photograph insects, but I’ve only recently started to try to really learn about them. It’s great that you put so much time into educating the clueless, like me.
Thanks again and warm regards,
No spanking was intended. Trust us when we humbly acknowledge that we are often wrong and we depend heavily on our readership to provide needed corrections to our own identifications
Letter 45 – Unidentified Asilid from Idaho
Subject: Bugged Birder
Geographic location of the bug: Pocatello, Idaho
Time: 04:03 PM EDT
Your letter to the bugman: Dear Bugman, While out birding in the disc golf course behind my house, this bug landed at my feet. It is about 1.5 inches as I recall. The furry legs caught my eye. I can find nothing on the internet that resembles it. The area is high desert with sage brush and juniper. I took this picture on June 26. Thanks.
How you want your letter signed: J. Shipman
Dear J. Shipman,
This magnificent predator is a Robber Fly in the family Asilidae and we believe it is in the subfamily Asilinae. There are numerous similar looking individuals on BugGuide.
Hey, thank you so much, and for such a prompt answer! I Checked out BugGuide, as you suggested, and also found a lot of info about Robber Flies on Wikipedia. Gosh, what a brute! Are they found only in the West? I’m originally from the East Coast, and I’ve never heard of these guys. Cheers – J
Letter 46 – Robber Fly
Location: Sandwich, MA, Cape Cod, USA
July 16, 2011 3:13 pm
Hi, I found this guy on my porch rail this morning here on Cape Cod in Massachusetts. It was a cool July morning and the insect was sluggish enough to pose for a good shot. Can you tell me what it is? And is it a biting insect? Its mouthparts remind me of those of a horsefly.
Signature: Tim Crowninshield
We are starting to go cross-eyed we have looked at so many Flies on BugGuide, and like you, we haven’t a clue as to the identity of this stunning Fly. Something makes us think it is a predator, and possibly a Robber Fly, but that is just a hunch. We will try to contact Eric Eaton to see if he is able to assist in an identification.
It is indeed a robber fly, Ommatius tibialis most likely:
That “bump” on the front margin of the wing is pretty diagnostic it would appear.