Robber Fly Bite: Is It Poisonous? Facts You Need to Know

Robber flies are fascinating insects known for their predatory behavior and large size, often mistaken for horse flies or other biting flies. Although fierce hunters in their own right, attacking various insects such as butterflies, wasps, and grasshoppers, they are not blood feeders and typically do not pose a threat to humans when left alone ncsu.edu.

However, it is important to note that some larger species of robber flies can inflict a painful bite if mishandled wisconsin horticulture. Despite the pain associated with their bite, robber flies are not venomous like certain snake bites cdc – meaning their bite will not deliver toxins into your system. As a rule of thumb, the best way to avoid any unpleasant interactions with robber flies is to observe from a safe distance and give them the respect they deserve as skilled predators in the insect world.

Robber Fly Bite: Is it Poisonous

Venom and Neurotoxins

Robber flies are known to be efficient predators, capturing and consuming other insects. However, their bite is not considered poisonous to humans. Although robber flies do utilize venom to paralyze their prey, this venom is not harmful to humans and does not contain neurotoxins.

Example:

• Robber flies use venom to immobilize insects such as bees and wasps, which they later consume.

Comparison with Other Insects

Comparing robber flies bites to other insects, it is evident that they pose a relatively low risk.

Comparison table:

While a venomous snake bite delivers venom containing harmful neurotoxins that can lead to severe symptoms or even death in humans, a robber fly bite is considered non-poisonous. Horse flies, in comparison, may deliver a painful bite, but their bite is also not poisonous.

Characteristics of robber fly bites:

• Painful, but not poisonous
• Venom utilized only for immobilizing their insect prey

Remember, despite their intimidating appearance and painful bite, robber flies do not inject venom or neurotoxins harmful to humans.

General Overview of Robber Flies

Appearance and Identification

Robber flies, belonging to the family Asilidae, are a diverse group of predatory insects with varying sizes and colors. They typically measure between 0.2 to 2 inches in length, with wings that often resemble those of other insects like bees and wasps ¹. Some key features of robber flies include:

• Large, forward-facing eyes
• Strong, agile wings
• A long and pointed proboscis (tubelike mouth) used for attacking prey

For example, some robber fly species are brightly colored and can be mistaken for bees or wasps. This mimicry helps them ambush their prey with greater success.

Habitat and Distribution

Robber flies are found in various habitats across North America, particularly in areas with abundant vegetation and prey ². They are commonly observed perched on exposed surfaces, waiting for an opportunity to snatch a passing insect. The distribution of robber fly species can vary depending on their preferred habitat and prey. Some examples of habitats that robber flies inhabit include:

• Forest edges
• Meadows
• Gardens
• Agricultural fields

In conclusion, robber flies are a fascinating and diverse group of predatory insects with unique appearances and wide distribution across North America. Their ability to mimic other insects like bees and wasps and their knack for ambushing prey make them an interesting subject for further study.

Feeding and Predation Habits

Hunting Techniques

Robber flies are skilled predators, using various techniques to capture their prey. One common method is the ambush attack, where they wait on perches and surprise their victims. Another tactic involves aerial pursuits, where robber flies actively chase down insects mid-flight.

Common Prey

Robber flies have a wide range of prey, including:

• Insects: They primarily feed on other insects, making them beneficial for controlling pest populations.
• Grasshoppers: These large, hopping insects are a common target for robber flies.
• Wasps: Despite their stingers, wasps can still fall victim to the ruthless robber fly.
• Bees: Even bees, capable of stinging in defense, are not immune to the robber fly’s attacks.
• Other flies: Smaller flies, such as house flies and fruit flies, may also be consumed by robber flies.
• Dragonflies: These agile, flying predators can become prey themselves when facing a hungry robber fly.

Life Cycle and Development

Larval Stage

• Robber fly larvae live in the soil
• They feed on eggs, larvae, and soft-bodied insects

The larval stage of the robber fly begins as a tiny egg, hatching into a legless, worm-like creature. Living below ground, these larvae are predators, consuming a range of small insects and their eggs. Examples include beetle larvae, aphids, and mites. This stage lasts several months, with the larvae growing and molting into a larger form before pupation takes place.

Adult Stage

• Robber flies have a distinct, tapering abdomen
• Predatory with strong, bristled legs

In the adult stage, robber flies develop a tapering abdomen and strong, bristled legs to aid in prey capture. These predators are known for their aggressive nature, attacking a wide variety of insects such as butterflies, wasps, beetles, and other flies. They do have sharp mouthparts and can deliver a painful bite, but it is not poisonous. Instead, the adult robber fly injects its prey with a saliva containing enzymes that paralyze and digest the victim’s tissue.

Robber Fly Bite Comparison Table

In summary, the life cycle of the robber fly consists of a soil-dwelling larval stage, where they consume various small insects and their eggs, followed by an adult stage, where they are aggressive predators with strong, bristled legs and a tapering abdomen. Although robber flies can deliver a painful bite, it is not poisonous and is solely used for prey capture.

Importance and Benefits

Robber flies are a beneficial group of insects. They contribute greatly to the ecosystem, particularly in grasslands.

• Predatory nature: They are fierce predators, preying on a variety of insects, such as bees, wasps, dragonflies, spiders, and beetles.
• Biological control: Their predatory nature helps maintain a balance within the ecosystem, by keeping the population of pests in check.

Robber flies come in various colors and sizes, ranging from 0.2 to 2 inches. Some even mimic other insects like bumblebees and wasps. This makes them efficient in capturing prey.

Their bite, however, is not considered poisonous to humans. These predators inject venomous saliva into their prey, but its effects on humans are generally very minimal. Biting humans is typically not a concern, as they only bite if mishandled or threatened.

In conclusion, robber flies play a crucial role in maintaining the balance in ecosystems like grasslands. They are beneficial to the environment as they help reduce the population of pests and other harmful insects. However, they are not a threat to humans in terms of poisonous bites, making them a valuable part of our natural surroundings.

Symptoms and Treatment of Robber Fly Bites

Symptoms and Allergic Reactions

Robber flies are not poisonous, but their bite can be painful due to their strong mouthparts used for capturing prey. Some individuals may experience itching and swelling at the bite site. In rare cases, a person may have an allergic reaction to the bite, potentially causing symptoms such as:

• Hives
• Nausea
• Swollen lymph nodes

Treatment Options

Treatment for a robber fly bite primarily involves managing the pain and itching. Some options include:

• Applying a cold compress to reduce swelling
• Using over-the-counter antihistamines to alleviate itching

In case of an infection, a doctor may prescribe antibiotics. If you experience an allergic reaction, it’s essential to seek medical attention immediately.

To summarize, a robber fly bite can be painful and cause itching, swelling, and in rare cases, an allergic reaction. Treatment involves managing symptoms with cold compresses, antihistamines, and in some cases, antibiotics to fight infection.

Comparison with Other Biting Insects

Deer Flies and Tularemia

Deer flies are known for their painful bites, but they also have the potential to transmit tularemia, or rabbit fever. Some key points about deer flies and tularemia include:

• Deer flies are biting flies
• They can transmit the tularemia bacteria to humans
• Tularemia symptoms can range from mild to severe

Sand Flies and Leishmaniasis

Sand flies can transmit a parasitic disease called leishmaniasis. Here are a few aspects of sand flies and their role in spreading leishmaniasis:

• Sand flies are tiny biting insects
• They are responsible for transmitting leishmaniasis parasites
• Leishmaniasis can have varying symptoms and severity levels

Black Flies

Black flies, also known as buffalo gnats, are another type of biting insect. They do not transmit diseases like deer flies or sand flies, but their bites can be painful and cause irritation. Black fly bites can lead to:

• Painful swelling and itching
• Red welts on the skin

Biting Midges

Biting midges, also known as no-see-ums, are tiny insects that can cause discomfort when they bite humans. Here are some characteristics of biting midges:

• Biting midges are small, often less than 1/8 inch long
• Their bites can be painful and itchy

Stable Flies

Stable flies are another kind of biting insect that can cause annoyance and discomfort. They are similar to house flies but have a painful bite. Some key points about stable flies include:

• They are similar in size and appearance to house flies
• Stable fly bites can cause pain and irritation

Comparing these biting insects with the robber fly, also known as the assassin fly, they all differ in their behavior and impact on humans. While the robber fly does use venomous saliva to immobilize its prey (bees, wasps, dragonflies, spiders, beetles, and other flies), it is not considered harmful to humans unless mishandled (Smithsonian Institution). Therefore, robber fly bites do not pose the same risks as bites from other biting insects mentioned above.

Physical Characteristics

Robber flies are known for their unique physical features. They possess a prominent proboscis, which is a sharp tube or beak used for feeding. These insects also have large, widely-spaced compound eyes that aid in spotting their prey.

Another distinctive feature is the mystax, a patch of hair located on the robber fly’s face. This mystax helps protect them from potential retaliation by their prey. Moreover, they have antennae that assist in sensing their surroundings.

Here’s a quick comparison of some key robber fly features:

When considering robber fly bites, it is important to know that these insects are not poisonous. While they are fierce predators, their venomous saliva is only used to immobilize their prey, such as bees, wasps, and other insects. A robber fly is unlikely to bite humans, and if it does so, it is usually a result of being mishandled. So, even though they have a fearsome appearance, robber flies are not considered to be a threat to humans.

Reader Emails

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 – Carpenter Bee Robber Fly from South Africa

Large Unkown Fly
Location: South-Africa, Gauteng
February 4, 2012 4:40 pm
Dear Bugman,
I live in South Africa. We have a huge diversity in insects. I was in our town outside a clothing store, and there is this waste high, round steel barrier (about 3-4 inch wide) in front of it. As I waited outside the store an insect came and sat on this steel barrier… At very 1st I quickly thought it might be a bumble bee of some sort as it has quite a large size. It was black, very hairy and with 1 white stripe on its back above the wings. Upon closer inspection I realized that it was some sort of fly. I immediately took out my mobile phone and took 3 photos before it flew away. I have NEVER in my 30 years seen a fly like this and at such a huge size. Can you please tell me what it could be, as I think this might be a new species Insecta Diptera…
Thank you!
Signature: Eugène McLaren

Dear Eugène,
This magnificent predator is a Robber Fly in the family Asilidae.  We are not certain of the species, but it most closely resembles North American Robber Flies in the genus Laphria, the Bee-Like Robber Flies.  On BugGuide they are described as “most species are black and yellow mimics of bumble bees or carpenter bees.”  The Bee-Like Robber Flies look similar to the Bee Killers in the genus Mallophora, but they can be distinguished by their antennae.  According to BugGuide, the Bee Killers are:  “Large, fuzzy, bee-mimicking robber flies. Resemble Laphria, another genus of robbers that mimic bumblebees, but is even hairier and has antennae with a very thin terminal final segment, whereas Laphria has thick antennae.”  Your individual has the thick antennae.  Continued research revealed that this is an entirely different genus.  We believe we have correctly identified your Carpenter Bee Robber Fly, Hyperechia marshalli, by a description on the Google Books Field Guide to Insects of South Africa where it is described as:  “Large (wingspan 34-44 mm), stout carpenter bee-mimic, uniformly black with yellow to yellowish white band of hair on hind margin of metathorax.  Legs thickly covered with long hair.  Biology: “Rests and oviposits on tree trunks.  Adults hunt from dead trunks bored by carpenter bees.  They feed on carpenter bees and other bees and wasps.  Larvae bore and live in wood tunnels in association with carpenter bee larvae, on which they are reported to feed.”  We then found a matching image on Global Species.  There is a nice photo on FlickR and another on ZipZode Zoo.

Letter 2 – Giant Yellow Robber Fly from Western Australia, possibly

Giant Fly?
Thu, Feb 26, 2009 at 4:25 AM
I was sitting in my garden on new years day 2009 when this huge flying thing buzzed past my head, did a few loop the loops and settled on the frame of the swing we have in the back garden. I was amazed at the size as i measured it over 2 inches long. I grabbed my camera from inside and took this picture before it flew away at great speed. I have showed it to alot of locals and they have all said they have never seen anything so big before. Is this abnormal or some migrating insect from a far away land?
Mr B
Perth, Western Australia

Dear Mr B,
This is some species of Robber Fly in the Family Asilidae.  Robber Flies are predatory insects, and the larger species are quite capable of capturing bees in flight.  We haven’t had any luck identifying your species on one of our common sources for Australian insects, the Insects of Brisbane Website, but since you are in Perth, your insect might have a range limited to the western portion of the continent.  As we continued our research, we found the Giant Blue Robber Fly, Blepharotes spendidissimus, listed on the same website.  The Giant Blue Robber Fly looks very similar to your specimen.  Continued research revealed the Giant Yellow Robber Fly, Blepharotes coriarius, also on the Insects of Brisbane Website.  Closer inspection of your photograph seems to indicate the telltale golden yellow abdomen beneath the wings, which would confirm that this is probably a Giant Yellow Robber Fly.

Letter 3 – Possibly Biting Robber Flies in Texas

Subject:  Large Biting Fly
Geographic location of the bug:  Tyler, Texas
Date: 08/31/2019
Time: 12:08 PM EDT
Your letter to the bugman:  We see these ‘bugs’ usually in the fall. Their bite is painful and leaves whelps. Wasp killer spray does them in so we got pictures this time.
How you want your letter signed:  Bob & Elaine

Dear Bob & Elaine,
Normally we would expect a large biting fly to be a Horse Fly or a Deer Fly, and this looks more to us like a predatory Robber Fly, but we have not had any luck matching your images to a species.  While we caution readers not to carelessly handle large Robber Flies as they might bite, we do not know of any reports of unprovoked bites from Robber Flies.  We will be sending your images to Eric Eaton to get a second opinion on its identity.

Eric Eaton Responds.
Hi, Daniel:
Yes, it is a robber fly, but I suspect that it is guilty by association with something like a horse fly or deer fly.  Robber flies do NOT habitually bite people.  They are strictly predators of other insects.
Eric

Letter 4 – Carpenter Bee Robber Fly from South Africa

Subject: Big black fly with white stripes
Location: South Africa
March 14, 2017 5:40 am
Dear Bugman
I’m from South Africa. I saw this uge fly on my laundry . It seems like it was feeding on a smal bee. Is this a carpenter bee robber fly?
Signature: Yours sincerely, Gerrit

Dear Gerrit,
This is definitely a Carpenter Bee Robber Fly, Hyperechia marshalli, a species represented on our site in several previous postings.  We verified its identity on iSpot.  These impressive aerial predators have a particular fondness for preying on large, stinging insects.  Your individual appears to be eating a Paper Wasp.  The Carpenter Bee Robber Fly is also pictured on iNaturalist.

Letter 5 – Giant Yellow Robber Fly from Australia

Subject: Giant yellow robber fly from Western Australia
Location: Quinninup, Western Australia
February 23, 2017 3:14 am
I found this giant fly on a window, feet caught in spiderwebbing, 25km south of Manjimup. It is 45mm from head to tip of abdomen, is bright orange on the top of the abdomen and black and hairy underneath. It has tufts of black and white hairs down the sides of the abdomen and very strong black legs covered in barbs.
Signature: PK

Dear PK,
The Giant Yellow Robber Fly, Blepharotes coriarius, is one of the most impressive looking flies we have ever received for posting.  We were quite amazed the first time we posted an image of a Giant Yellow Robber Fly nine years ago.  It is one impressive predator.

Letter 6 – Giant Yellow Robber Fly from Australia

Subject: Giant yellow robber fly from Australia?
Location: -36.131866,146.926785
March 10, 2013 7:50 am
Hey there, I found a fly today (deceased) and took a few pictures of it. I was curious as to what the hell it was, so I searched and came up with your site featuring some examples of large flies with a yellow abdomen which looked fairly identical to the one I saw. This particular specimen was found on top of Huons Hill, Wodonga, Victoria, Australia. The large Mitsubishi key you see in a couple of the photos is exactly 92.9mm or 3.657” long.
Sorry about the poor photography, I only had an iphone with me, and couldn’t see the screen to ascertain whether or not it was focusing properly on the fly, which it wasn’t.
Feel free to contact me via email – thesixthwheel@gmail.com
Signature: Cheers, Nick.

Hi Nick,
We agree that this looks like a Giant Yellow Robber Fly, Blepharotes coriarius.  We received a comment on a posting last week and Wolfgang said he would send a photo, so we thought these might be the anticipated images, but we were mistaken unless you also wrote to us under a pen name.  Large Robber Flies are magnificent creatures and your photo of the underside of the body shows the long legs that can be used to snatch prey while in flight.

More images of the Giant Yellow Robber Fly can be found on the Brisbane Insect website.

Thanks for the reply. I am not Wolfgang, nor do I have anything to do with a posting from last week. Like I mentioned in my original communication to you, I had only found the fly on the same day (yesterday).
Are they rare to see? I’ve never seen one before.
Thanks for your time.

We are not certain how common Giant Yellow Robber Flies are in Australia.  Predators are generally not as common as prey.  By the way, the photography is just fine.

Letter 7 – Robber Fly bites Wife in North Carolina

Subject: Bug bit wife
Location: North Carolina
July 10, 2017 7:38 pm
Hey was just wondering what this bug was is
Signature: Ryan

Dear Ryan,
This is a predatory Robber Fly in the family Asilidae.  Robber Flies generally take prey on the wing, and large Robber Flies are capable of attacking large prey.  Robber Flies are not aggressive, but they do have mouths adapted to piercing the hard exoskeletons of insect prey, including Dragonflies and large Wasps, and then sucking fluids from the now dead prey.  We doubt this Robber Fly dive bombed and attacked your wife.  You did not provide much in the way of details, but we suspect perhaps this Robber Fly found itself trapped inside your wife’s clothing and then bit defensively.

Letter 8 – Australian Robber Fly

a strange bug from central australia
Hi Bugman,
We found this funny looking creature at our chook shed this morning. I thought it looked like Darth Vader! It has a very orange upper abdomen which it flashes when beating wings. It also has hairy and very long legs. It was about 5cm long. It has a proboscus like a cicada… My girlfriend thinks its a cicada…I think it’s a Star Wars character..! Help
Jay and Ada – Alice Springs, Australia

Hi Jay and Ada,
This swift flying predator is a Robber Fly. By the way, one of our favorite books is Ada by Vladimir Nabokov and it has hundreds of insect references.

Letter 9 – Mexican Robber Fly

Possible Brachonid Wasp
Hi,
I saw this Wasp-like insect this morning through my kitchen window near Benson, Arizona. It is large (maybe 2 – 3"), orange body, dark wings, white face with short red antenae. Two photos of this insect attached. I searched your pic and think this is in the Brachonid Wasp family. Thank you,
Carol Breton
Benson, Arizona

Hi Carol,
This is a Robber Fly, not a Brachonid Wasp. It sure looks like on of the Hanging Thieves in the genus Diogmites, but there are no exact species matches on BugGuide. We will contact Eric Eaton and Martin Hauser to see if either of them knows the species.

Update: (09/26/2007)
Hi Daniel,
I sent the pics to Eric Fisher, who knows everything about robbers (only the flying ones). He told me it is Archilestris magnificus (Walker), a Mexican species which has been only a few times collected in Arizon, but nowhere else in the US… It is not really a hanging thief, but it sure looks like one. Great catch! Cheers
Martin Hauser

Comment: (09/26/2007)
Wow! Hey, I think a friend of mine got one across the border in Nogales, Sonora, Mexico back in 1989. We were on vacation together, and this big robber fly was trying to get out of a storefront window. So my friend paid the dude for the fly! LOL! Wish I would have tried to outbid him:-) Hope we can get these images migrated over to Bugguide, as I’m sure it would be a new genus and species….but I also know how busy you are, Daniel. Maybe Eric Fisher can take a look at our Bugguide asilids and confirm IDs?
Eric Eaton

Letter 10 – Mexican Robber Fly in Arizona Redux

Mexican Robber Fly
I wrote you last year with this huge unknown insect and you
were able to id it as a Mexican Robber Fly; very rare and
only seen in Arizona and only a few times.
Well, he’s baaaack. I got one of these shots on August
26, 2008 and the second one on Sept. 01, 2008, at which time
I saw TWO of them fly away! I live in a remote desert area
bordering Cochise County, about six miles west of Benson,
Ariz., at an elevation of 4,600 feet. Love your site and use
it all the time to id bugs! Thanks for being there.
Best Regards,
Carol L. Breton
Benson, Arizona

Hi Carol,
Thank you so much for reporting this year’s sighting of Archilestris
magnificus (Walker).

Update: (09/07/2008)
Daniel: I don’t think that robber fly is “rare” any more. I collected one in Amado, Santa Cruz County, AZ just the other day, and saw another one at the same location. I think they are probably established in Arizona now.

Eric

Letter 11 – Attack of the Robber Flies

Wasp-moth monster

Wasp-moth monster
Location: Gordonville, Texas
July 4, 2011 2:13 am
I had 6 of these things attack me yesterday. This was the first one I found and took pictures of that wasnt mangled after i got ahold of it. I dont know if there is more of them around, but i think so. This happened July 3, 2011, midday, in north central texas, Gordonville, to be exact. No idea, but I’m a grown ass man and when 5 divebombed me, I almost peed myself. theres a postcard in the pic for size reference.
Signature: JTGrace

Dear JTGrace,
We are fascinated by your letter, and we have some information for you, and we plan to continue to research this matter.  This is a large Robber Fly, however, we are having difficulty identifying it on BugGuide.  It reminds us of a Hanging Thief in the genus Diogmites, or a closely related genus, because of its physical structure.  You can see other Hanging Thieves on BugGuide.  We could not locate any matches though, and the next subfamily that has members with a similar structure is Stenopogoninae, but again, not matches on BugGuide.  Our searches did lead us to this posting on BugGuide of Orthogonis stygia, and though we are quite certain it is not your species, this information is interesting:  “This species was named over 50 years ago on the basis of half a dozen females. Only one more female had been found since. However I have been finding males regularly in deep wooded canyons in the shady understory on well-rotted oak logs usually on a slope. The males are very possessive of their logs, even challenging humans who come too close, with wasp-like threat displays, and by following you around as long as you are present. I have found them in three east-Arkansas counties. If areas such as I have described are searched, it may turn out that this extremely rare robber fly is not so rare after all. Norman Lavers.”  Perhaps a group of male Robber Flies was defending territory in the hope of luring a mate, and that could explain the attack you experienced.  We have requested additional assistance with this interesting Robber Fly.

Eric Eaton Comments
Daniel:
I agree it is something related to a hanging thief, but maybe not in that genus….Can’t explain the behavior he is describing, unless they were actually catching mosquitoes or some other insects that were in close proximity to the people…..
Eric

Robert Cannings Responds
Hi Daniel:
Eric Fisher and I both say it’s a Saropogon [See BugGuide]species. Eric, who’s much better at these than me, thinks it’s probably S. dispar, which is common in parts of Texas.  As for the 5 or 6 dive bombers, ….. Honestly, we can’t understand what might have happened.
Regards,
Rob

Ed. NOte: Last summer, both Robert Cannings and Eric Fisher assisted in identifying another member of the genus, Sarpogon combustus.

Letter 12 – Drawing of a Robber Fly, we presume

Large Stinging Insect
Location: Inside a DSW Shoe Store, Durham, NC, USA
August 5, 2011 11:02 pm
Hello, I saw this bug in a DSW shoe store and was wondering what it was. I don’t have a picture of it, but I tried to draw it. I know it looks bad but I’ll try to describe it. It was probably about 1.5 to 2 inches long, and maybe a bit less than half an inch wide. It had large black eyes, a nose like thing in between, and a slightly furry dark green/brown head. The wings were clear and narrow, and reached about to the ed of the bug, although not past the stinger, which was large, about one centimeter. The abdomen was narrow. That’s the best I can describe it. Sorry I can’t give a picture.
Thanks a lot,
-Emma

Did it actually sting you or someone you know of?

No, I had just never seen anything like it before. But I look through some of the pictures on your website, and I think that it might be a robber fly.
Thanks!
-Emme

That was our first guess, however we needed to verify that there was just the perceived threat of a sting versus an actual sting.  Robber Flies do not sting, but many people mistake the ovipositor of a female for a stinger and Robber Flies are frequently mistaken for wasps.

Letter 13 – Giant Yellow Robber Fly from Australia

Subject: Robber Flies from Australia
Location: Boddington/Crossman western Australia
January 12, 2013 11:28 pm
photos in regards to ”Giant Yellow Robber Fly from Western Australia, possibly” from Trent.
Signature: photos posted on Giant Yellow Robber Fly from Western Australia, possibly

Hi Trent,
Thanks for sending your photo of a Giant Yellow Robber Fly, Blepharotes coriarius.  It nicely compliments the original posting you supplied comments for.

Letter 14 – Ovipositing Robber Fly

Subject: Ovipositing Robber Fly
Location: Andover (Sussex Cty) NJ
July 20, 2014 5:51 am
I just thought I’d send this photo along to you because it was something I’d not seen before. I was walking on a lakeside trail looking for dragonflies when I saw this large robber fly ovisositing. She was so large that initially I thought she was a small dragon. I was able to crouch down and watch her for several minutes.
Signature: Deborah Bifulco

Hi Deborah,
Thank you for supplying us with this marvelous documentation of a Robber Fly in the act of ovipositing.  According to BugGuide:  “Adults lay eggs in the soil or in plants. A few, such as Mallophora and Megaphorus form an egg mass on a plant stem. Larvae often predatory, consuming eggs and larvae of other insects in decaying matter. Typically overwinter as pupa, emerge in spring. Life cycle is 1-3 years.”

Letter 15 – Male Robber Fly

Subject: Flying Insect
Location: South Texas
May 8, 2016 10:56 am
I live in a rural area & saw the insect in the attached photo for the first time yesterday evening. Am hoping you can help to identify it.
Signature: Cindy

Dear Cindy,
We believe the tufts at the tip of the abdomen of the individual in your image indicate it is a male in the genus Efferia, possibly Efferia albibarbis based on this BugGuide image and this BugGuide image.  Robber Flies are important predators that often take prey on the wing.

Letter 16 – Jogger Reportedly Pursued by Robber Flies!!!

Subject: Asilidae feeling threatened by scent?
August 4, 2016 1:36 am
Just this morning, I went running down at Palo Duro Canyon in Canyon Texas.  The entire run (2.2 miles), I experienced aggressive behavior from Robber Flies (Asilidae). They literally preyed on me the entire run, consistently going for my legs and hair.
I can’t tell if the aggressive behavior was from me running or from the new Tea Tree shampoo that I just started using. I go on runs all the time in Palo Duro and never before have experienced this. Perhaps the behavior wasn’t aggressive, still this is new territory.
My real question is, has all this branched out from me switching to this new shampoo? I look forward to hearing back from y’all.
Signature: Samuel  Tenny

Dear Samuel,
We wish you had sent an image to illustrate your query as it would make our response more definitive.  Lacking an image, we have taken an image from our archives of Courting Belzebul Bee Eaters, Mallophora leschenaulti, a large species of Robber Fly found in Texas, to illustrate the posting.  Texas has many large, predatory Robber Flies and we could easily have chosen the magnificent Heteropogon patruelis, also from our archives, as the illustration.  Robber Flies do not normally exhibit aggressive behavior towards humans, so we have our doubts that members of the family Asilidae are the culprits.  We would tend to favor blood-sucking Horse Flies, which can also get quite large, and which may have not had any nearby livestock or deer upon which to feed, causing them to turn their attention to the nearest large, warm-blooded meal they encountered, namely you.  We say this from experience since our editorial staff was chased by large Horse Flies back in our youth in Ohio, and they even landed on the hood and windshield of the car once we had taken shelter.  Please look at some images of Horse Flies and get back to us if you think our suspicions are correct.  With that said, chemicals in shampoo, as well as scents in colognes, perfumes and antiperspirants, have been reported to attract bees and wasps, so that is a distinct possibility that they might attract Robber Flies as well.  If the shampoo is the cause, we would also question why your aggressive flies were targeting your legs.

Letter 17 – Giant Yellow Robber Fly from Australia

Subject:  Giant Robber fly.
Geographic location of the bug:  Numurkah Victoria
Date: 01/26/2019
Time: 03:06 PM EDT
Your letter to the bugman:  Gday to be buggered I could fine any relation to this bug.
Then your site popped up.
I have sighted this fly several times in the last month or so.
Different locations around our 60acres.
It’s massive. It’s loud. It’s soooo fast. I had to take a slow mo video of it.
Any way would like to know anything you have on this sucker.
How you want your letter signed:  Sorry not sure on this question.

We have always found the Giant Yellow Robber Fly, Blepharotes coriarius, from Australia to be an extremely impressive Robber Fly.  The Australian Asilidae site also pictures several other similar looking species.  Your individual appears to have a tufted abdomen, indicating it is a male, and it really does most resemble the image of the male Blepharotes coriarius pictured near the top of the page. 

Letter 18 – Male Robber Fly

Subject:  Large Fly?
Geographic location of the bug:  Coryell County
Date: 04/13/2019
Time: 05:58 PM EDT
Your letter to the bugman:  Hello! This large fly-like insect sat on our porch for several hours. I don’t know if it was injured, but it didn’t move much. I have been unable to match its photo. Thank you!
How you want your letter signed:  Ellen

Dear Ellen,
How nice to hear from you.  This is one of the predatory Robber Flies in the family Asilidae.  Because of the tufted abdomen, we are inclined to speculate that this is a male Robber Fly in the genus Efferia, and though its markings are different, you can see that it resembles this individual on BugGuide.

Letter 19 – Green Eyed Robber Fly

Subject:  What is it?
Geographic location of the bug:  Central Texas
Date: 06/25/2021
Time: 10:52 AM EDT
Your letter to the bugman:  I found this on its back and decided to spray it as it looks mean! It has a long needle-like nose and long thin wings, only two though.
How you want your letter signed:  Thanks, Russell

Dang Russell.  That is one large Robber Fly.
We are quite confident you encountered the Green Eyed Robber Fly, Microstylum morosum, and according to Zoo Safari USA: “Very little is known about this species, but it is the largest of the Robber Flies in North America.”  Here is a BugGuide image.  You might want to contact your local natural history museum to see if they want the specimen.