Robber Fly vs Wasp: Uncovering the Key Differences

Robber flies and wasps might look similar at first glance, but there are some key differences between these two types of insects. While both are predators in the insect world, their physical features and behavior set them apart.

Robber flies, also known as assassin flies, are part of the Diptera order, which means they have two wings. These predatory insects have a long, tapered abdomen and a humpbacked appearance. Their legs are spiny, their face often appears bearded, and their mouthparts consist of a pointy, knifelike proboscis. These flies use their agile flying skills to catch their prey in midair. Species of robber flies vary in appearance, with some even mimicking the appearance of wasps and bees ([source)].

On the other hand, wasps belong to the Hymenoptera order, which includes bees and ants as well. These insects have four wings and a characteristic narrow waist that separates their thorax from their abdomen. Unlike robber flies, wasps build nests and can either be solitary or social. Their mouthparts are designed for biting and chewing, and they also possess a stinger for defense and hunting purposes.

Robber Flies and Wasps: An Overview

Classification and Appearance

Robber flies and wasps are both insects, but they belong to different orders. Robber flies (family Asilidae) are part of the order Diptera, while wasps belong to the order Hymenoptera.

• Robber flies:

  • Medium to large-sized flies (3/8 to 1-1/8 inches)
  • Gray to black, sometimes mimicking wasps or bees
  • Hairy-bodied with a long, narrow, tapering abdomen
  • Examples: Assassin Fly, Robber Fly¹

• Wasps:

  • Varying sizes and colors
  • Distinctive narrow waist and two pairs of wings
  • Cylindrical abdomen with a stinger at the end
  • Examples: Paper Wasp, Yellow Jacket²

Comparison Table

Habitat and Range

• Robber flies:

  • Found in various habitats, often on plants’ stems or the ground³
  • Known to live in the United States, including areas like North Carolina³

• Wasps:

  • Live in diverse environments, often in nests built for protection⁴
  • Widespread throughout the United States, including North Carolina⁴

In both cases, they inhabit regions where they can easily find prey to feed on¹².

Physical Adaptations

Wings and Flight

Robber flies:

• 2 wings
• Fast and agile in flight

Wasps:

• 4 wings
• Greater lift capacity

In terms of wings and flight, robber flies have two wings, which allows them to catch their prey with agility and quickness. Wasps, on the other hand, possess four wings providing them with greater lift capacity.

Eyes and Vision

Robber flies:

• Large compound eyes
• Excellent vision

Wasps:

• Large compound eyes
• Good vision, rely on warnings from colors

Both robber flies and wasps have large compound eyes, which provide them with strong visual capabilities. Robber flies have excellent vision, allowing them to spot and chase prey. Wasps also have good vision but rely more on warnings from colors, particularly when it comes to identifying potential predators.

Mouthparts and Feeding

Robber flies:

• Piercing and sucking mouthparts
• Predatory diet (including bees, wasps, and other insects)

Wasps:

• Chewing mouthparts
• Predatory and/or nectar-feeding diet (depending on species)

When it comes to feeding, robber flies have piercing and sucking mouthparts and a predatory diet, feeding on other insects, including bees, wasps, and spiders. Wasps have chewing mouthparts, and their diet can consist of other insects, nectar, or both, varying by species.

Behavior and Diet

Prey and Predation

Robber flies:

• Predators of flying insects, such as spiders and grasshoppers
• Catch prey mid-air

Wasps:

• Predators of insects like caterpillars
• Also eat nectar and pollen for sustenance

Mimicry and Defense

Robber flies and wasps have developed unique ways to protect themselves and hunt for prey.

Robber Flies

• Bee and wasp mimics
• Long legs and distinctive bearded face
• Humpbacked appearance

Wasps

• Bright body colors
• Warning markings
• Stinging capability

Comparison Table

These predacious insects display fascinating adaptations in their behavior and diet, showcasing the diversity and complexity of their survival strategies.

Life Cycle and Reproduction

Eggs and Larvae

• Robber Flies: Females lay eggs in soil or decaying wood¹. The hatched larvae are predaceous, feeding on other insect larvae².
• Wasps: Female wasps lay eggs on or inside a host (e.g., spider egg sacs)³. The tiny wasp larvae feed on the host, such as spider eggs⁴.

Development and Adult Stages

• Robber Flies:

  • Adult robber flies are medium to large in size⁵.
  • Their habitat includes pastures and sunny areas⁶.
  • They prey on flying insects, including other flies⁷.

• Wasps:

  • Wasp mantidfly species are smaller than robber flies⁸.
  • They are commonly found in gardens, fields, and meadows⁹.
  • Adult wasps feed on nectar and are not predatory¹⁰.

Comparison Table:

Ecological Role and Interaction

Beneficial Insects in the Garden

Robber flies and wasps serve essential roles in the garden by helping control various pest populations. They both act as predatory insects preying on garden pests like beetles, ants, and aphids.

For example, wasps, especially paper wasps, are known to feed on caterpillars and other insects harmful to plants. In contrast, other wasps like parasitic wasps lay their eggs on or in specific pest insects, benefiting the plants.

Similarly, robber flies are important predators of flying insects, including beetles and aphids. They also feed on various insect larvae that might damage plants in your garden.

Pest Control and Management

To efficiently use these beneficial insects for pest control, it’s essential to provide them with a supportive habitat. Encouraging the presence of robber flies and wasps starts with having a diverse garden, including flowering plants that attract them.

Some ways to create a favorable environment for beneficial insects include:

• Planting a variety of flowering plants that provide pollen and nectar
• Using non-toxic methods of pest control to avoid harming beneficial insects
• Providing shelter and nesting sites for robber flies and wasps, such as deadwood or untreated wood piles

A comparison table of robber flies and wasps as beneficial insects in the garden:

By promoting a healthy and diverse garden environment and understanding their ecological roles, you can harness the pest control potential of beneficial insects like robber flies and wasps for a balanced and thriving ecosystem.

Identification and Observation

Physical Features and Characteristics

Robber Flies:

• Robber flies have a distinctive bearded face and concavity between the eyes.
• They often have long legs and a long, tapering abdomen.
• Some species mimic bees and wasps.

Wasps:

• Wasps have a head, thorax, and abdomen, connected by a thin waist.
• They have antennae and six legs.
• Coloration varies but many are black, brown, or yellow.

Comparison Table:

Where to Find and Observe

Robber Flies:

• Associated with soil or decaying wood.
• Larvae prey on other insect larvae.
• Active in July and August, especially in places like Iowa.

Wasps:

• Common in gardens and woodlands.
• Nest in trees, underground, or buildings.
• Can be observed from spring to fall, but peak activity in late summer.

Example:
During July and August, you might see a robber fly perched on foliage, mimicking a wasp, while a nearby wasp might be flying around a nest in a tree.

Additional Resources

Photographic Guides and Image Galleries

For a better visual understanding of robber flies and wasps, consider exploring these resources:

• BugGuide: An extensive online photographic guide covering North American insects, including robber flies and wasps. You can find images, taxonomy, and general information about each insect family.

• Extension Office websites: Several university extension offices provide detailed photographic guides to insects commonly found in their regions, such as North Carolina State University’s gallery of robber flies.

Expert Organizations and Naturalists

For more in-depth information about robber flies and wasps, consult expert organizations and naturalists:

• Entomological Societies: Groups like the Entomological Society of America offer knowledge about various insects, including robber flies and wasps. They often publish scientific studies and provide access to experts in the field.

• Naturalist Blogs and Websites: Many passionate naturalists share their expertise and experiences with insects on blogs and websites. For example, naturalist Eric R. Eaton offers insights about many insects, including robber flies and wasps.

Comparison Table

Key Differences

• Robber flies have 2 wings, while wasps have 4 wings.
• Robber flies have a prominent beak-like proboscis for feeding, while wasps have mandibles for biting or stinging.
• Robber flies have a hairy body and long tapering abdomen, while wasps usually have a smooth body and narrow waist.
• Robber flies are predaceous and feed on flying insects like leafhoppers and white grubs, while wasps can be omnivorous and feed on insects, larvae, and sometimes plant nectar.

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 – Tachinid Fly

Unknown insect in near the flowers/deck
August 17, 2009
This thing spent most of its time flying about in the flowers, obscuring my view of it. Managed to get this shot when it finally landed on a piece of wood. I thought it might be some sort of wasp but can’t see a stinger.
Eric
Curlew, Washington (just below the Canadian border)

Hi Eric,
We spent a few minutes browsing through the family Asilidae on BugGuide, without any luck identifying what we believe to be a Robber Fly.  Though we found numerous individuals with this color pattern, we could not find a conclusive match.  We will try to get some assistance from Eric Eaton to identify the species, or at least the genus.
Correction from Eric Eaton
Daniel:
The “robber fly” is actually an atypical tachinid fly, genus Cylindromyia.  Great shot of it, too!  This page from BugGuide gives more information, and there is an “images” tab at the top for more pictures.
Keep up the great work!
Eric

Thanks Eric,
We were going to research Tachinid Flies before posting, but time was running short.

Letter 2 – Robber Fly

WHAT IS THIS?!?
Ok Bugman, I live in North Scottsdale, AZ. I was at work the other night and one of our regular customers came inside and said, "excuse me, but can you tell me if this is a spider or a bird?" Bugman, I am not squeamish around almost any insect (well, except centipedes, but I think everyone should be), but this thing is horrific. I’ve lived here all my life and have never seen anything like it. And by the pictures, you can tell it was devouring a bee. Later, it dropped the bee, which was still barely alive, and mostly hollow. What the…? Please help, I am extremely curious. Check out the few attached photos. Hope to hear from you soon.
Creeped out,
Chelsea
PS-: It had a feather like hump, short antennae, a grasshopper/segmented like body, spiny legs, and huge eyes. I’ve studied biology, and I don’t get the conglamorate parts of this creature!

Hi Chelsea,
Great photo of a Robber Fly. These are predators that will devour many types of insects. They are also capable of biting painfully.

Letter 3 – Robber Fly

Suffolk, VA black and white banded fly, elongated curved tail.
Location: Suffolk, VA USA
June 1, 2011 11:55 am
I found this fly hanging out by our garage mid-morning. I cannot find any pictures of it. As you can see from the pic, it has 6 legs. There is a shadow that makes it look like it has 8 legs. It’s tail was curved at the end. It was sluggish and did not fly away when my dog sniffed at it. I appreciate your help in identifying this insect. We live in a swampy area, summers are long and hot, and winters are mild here. We do not live near brackish water. Mostly all of it is fresh. Thanks in advance for your help.
Signature: Arlene Nygaard

Hi Arlene,
This is a Robber Fly and the morphology of the abdomen indicates that it is a male.  We haven’t the necessary skill to provide you with a definitive species identification, however, this photo on BugGuide of Efferia albibarbis is similar enough to be able to assure you that our general identification is correct.  Perhaps one of our readers will be able to supply more specific information.

Letter 4 – Robber Fly

What is this bug?
Location: Athens, GA
August 4, 2011 5:55 pm
Hi there! This guy has been hanging out on my back porch for a couple days now, and I have no clue what he is! Sort of a fly/bee/hornet hybrid. Really curious to get him ID’d. These photos were taken today, Aug. 4, 2011.
Signature: Michelle G.

Hi Michelle,
This is some species of Robber Fly in the family Asilidae.  They are amazing predators that catch their prey on the wing.  We believe your Robber Fly might be Proctacanthus fulviventris based on photos posted to BugGuidebecause the legs, antennae, wings and abdomen appear to match.

Wow, thanks! I looked up Robber Fly and I actually believe this guy
might be Promachus rufipes… you can’t tell in the photo I took, but
the length of his tail is striped yellow and black…which is why I
thought he was a hornet at first!
Thanks so much!! I’ve really enjoyed learning about these carnivorous
insects. I had never heard of Robber Flies before.
Michelle

Hi again Michelle,
We entertained that possibility.  We really wanted it to be the Red Footed Cannibalfly, but it appears that the feet are not as red as most individuals on BugGuide.  A good side view would help us, but there is probably enough for a real Robber Fly expert to determine the species.  Perhaps someone will write in to confirm.

Letter 5 – Robber Fly

crazy looking bug
Location: atlanta georgia
August 24, 2011 10:57 am
On a rainy summer day in Georgia, I find two of these fast flying bugs in my car. The other was larger than this, but I managed to get it to fly out a window.
Signature: dj

Hi dj,
Crazy Bug?  What about the crazy photo.  It is truly an awesome photo of a Robber Fly.

Letter 6 – Prairie Robber Fly

hey got a doozy
Location: near derby ks
August 31, 2011 8:08 pm
We have these big guys flying all around our house. At first i thought it was some kind of hornet but I got this up close one just before sundown. I tried looking it up to no avail. Just really wondering. Looked really icky on my 42 inch large screen when i hooked my camera up to it. All the little ”hairs” on the legs were so weird.
Signature: Heebby Jeebies

Dear Heebby Jeebies,
We were just going to try to classify this Robber Fly to the genus level and tell you it was a Hanging Thief in the genus Diogmites, however, we believe we might be able to do one better and identify it as a Prairie Robber Fly, Diogmites angustipennis, based on photos posted to BugGuide.

Letter 7 – Robber Fly

Subject: Type of fly?
Location: Chicago-area, Illinois, USA
June 24, 2012 12:52 pm
We saw this insect on my father’s water bottle and were fascinated and appalled in equal measure. As I took one entomology course in college, I was expected to instantly identify this mysterious bug. My response that it was a ”fly/wasp thing” did not impress. Please help me regain credibility,
Signature: Robin

Hi Robin,
This is a predatory Robber Fly, and we believe we have correctly identified it as Efferia aestuans thanks to images posted on BugGuide.  Since it is lacking an ovipositor and has a tufted abdomen, we can conclude that this is a male.

Letter 8 – Robber Fly

Subject: Modernist Bug
Location: Vail, AZ
July 4, 2013 11:28 am
This is the first of this kind I have noticed. Was photographed on the Arizona Trail near Three Bridges. Landed in front of me like a grasshopper.
Signature: Carl

Hi Carl,
This is a Robber Fly and your individual is one impressive looking predator.  We are not certain of the species, but it does resemble members on the genus Polacantha pictured on BugGuide where the information provided states that Polacantha arctuata is found in Arizona.  All of the photos on BugGuide of the species are males and we cannot locate any photos of females.  We believe your Robber Fly is a female.  We cannot locate any other images of Polacantha arctuata on the internet.  Your individual appears to lack the striped abdomen found on Promachus sackeni which is pictured on BugGuide.  While we cannot be certain of the species, we can tell you that Robber Flies are very adept predators and they often take large winged prey in flight.  Many species feed on large bees and wasps.  Perhaps one of our readers will have better luck with a species identification.

Wow! Thank you!

Eric Eaton Responds to our request
Daniel:
Eric Fisher is the go-to person for robber flies.  I’m sorry, I don’t have his e-mail address in my contact file….
This one appears to be a male in the genus Proctacanthus, if I know anything at all (which is sometimes suspect with asilids!).
Eric 

Letter 9 – Probably Robber Fly

Subject: I’m guessing it’s a robber fly. Am I right or wrong?
Location: Little River, Va
July 28, 2013 4:46 pm
This is the first time I have encountered this insect.
It flew into our cabin & would not leave.
I was scared to mess with it too much because it looks like it could fight back.
After some googling, I am guessing it is a robber fly.
Am I right or wrong?
Thank you.
Signature: Heather

Dear Heather,
We apologize for the tardy response.  We spent a bit of time trying to identify your insect, which we also believe to be a Robber Fly, but we were unable to find an identification prior to leaving town for two and a half weeks.  Then time just got away from us and we never created the posting which we have now remedied.  We will send this image to Eric Eaton to see if he can provide any information.

Letter 10 – Robber Fly

Subject: Giant mosquito! (seriously!)
Location: Houston, TX
October 15, 2013 2:19 am
Walked up to my front door on the west side of Houston, TX at 3 am, and the temperature was 23°C. Heard a loud buzzing, similar to a mosquito’s (but louder). Spotted it, and watched it land on a bush, so I swatted it in the attempt to stun it. Insect is still alive in these photos, but I think I did more than stun it. Insect is flying, is almost exactly 1 inch in length, has a sucker that seemingly could be a proboscis (did not wait around to see if it bites), however it didn’t seem to have any interest in biting me.
Thanks for your time, and I hope I haven’t discovered a mutant mosquito.
Signature: Hunter Mallette

Dear Hunter,
This is a predatory Robber Fly in the subfamily Dasypogoninae which contains the Hanging Thieves in the genus Diogmites as well as other similar looking genera.  Hanging Thieves get their name because they often hang from a single leg while feeding.  It looks somewhat like this Diogmites angustipennis pictured on BugGuide.

Daniel,
Thank you for your time and insight. I’m always finding interesting bugs and have the hardest time identifying them. You’ve saved me a great deal of frustration, and satisfied my curiosity.
Thank you,
Hunter

Letter 11 – Robber Fly

Subject: Unknown Fly
Location: Great Salt Lake, Utah
July 5, 2014 3:22 pm
While on vacation, I stopped at the Great Salt Lake in Utah. On the shores of the lake, there was these flies that were about 1 1/2 inches in length and were large enough to cast a shadow as they were flying. I am somewhat familiar with insects but I haven’t seen any like these before.
Signature: Brandon

Dear Brandon,
This is a Robber Fly in the family Asilidae, and we will attempt a more specific identification later today.

Letter 12 – Robber Fly

Subject: West Texas
Location: West Texas
May 25, 2015 12:55 pm
What is this strange bug? We have had a lot of rain lately, located in West Texas. Very interesting insect…
Signature: Ashley Jones

Dear Ashley,
This Robber Fly in the family Asilidae is an accomplished predator.  Based on images posted to the Plants and Insects of Goodwell and Texhoma site, this is a male Efferia aestuans, a species with no common name.

Letter 13 – Robber Fly

Subject: Is this related to a dragonfly?
Location: Dripping Springs, TX
August 23, 2015 9:18 pm
I live in the hill country of South Texas (west of Austin) and saw this while watching my humming birds on the back porch. At first I thought it was some sort of a dragon fly but after a closer look realized it wasn’t but have never seen something like this especially with the fuzzy tail.
Signature: Diana

Dear Diana,
This Robber Fly in the family Asilidae is not even closely related to Dragonflies, but they are both predators that catch prey on the wing, which may have resulted in some evolutionary similarities.  We believe your individual is in the genus Efferia, perhaps in the Albibarbis group which is pictured on BugGuide.  There are many nice images of Robber Flies from the genus Efferia on Greg Lasley Nature Photography.

Letter 14 – Robber Fly

Subject: Wasp? Bee?
Location: Suwanee, GA
June 21, 2016 7:58 am
This beastie was resting on my mailbox. An inch long, maybe. No visible stinger.
Signature: Anthony Trendl

Dear Anthony,
Our money is on this being a Robber Fly in the family Asilidae, and many members of the family mimic bees and wasps, but alas, we have not had any luck with a conclusive species identification.  The closest match we could find is Cyrtopogon lutatius pictured on BugGuide, and we suspect your “beastie” is closely related.  We will attempt to get a second opinion on this.

Eric Eaton provides feedback:
This is more likely an Atomosia sp.
http://bugguide.net/node/view/20268
Not uncommon in the eastern U.S., though you don’t say where it is from.
Eric

Thanks … I’ll look it up. I’m near Atlanta, in a burb just northeast of it. Suburbs but I have a lot of trees as creeks nearby.
I’d love to buy a book (books) focused on the fauna of this area. Any recommendations?
Tony

Hi Tony,
Specifically regional guide books are not that common.  We recommend The Kaufman Field Guide to Insects of North America.  A WTB? contributor, Eric Eaton is one of the authors.

Letter 15 – Robber Fly with prey

Subject: robber fly?
Location: Bloomington, Indiana
June 29, 2016 2:56 pm
I’m assuming this is a robber fly, but wondering for sure.
This photo was taken on June 29, 2016
Thanks!
Signature: Teddy Alfrey

Dear Teddy,
Was this a small fly?  We believe we have correctly identified it as the Robber Fly Cerotainia albipilosa based on this and other BugGuide images and its size is listed as less than five millimeters.

Daniel,
Thanks for the quick response!
I post quite a few of my photos on Facebook and would like to ID the various bugs and plants that I find myself photographing, more and more.
Five millimeters is about right. I was thinking a little less than ¼” long, including wings.
Thanks again!!
Teddy

Letter 16 – Unknown Robber Fly from Costa Rica

Subject: Bug from Costa Rica
Location: Monteverde, Costa Rica
July 17, 2016 6:36 pm
Hi Bugman,
I’m a biologist and photographer currently on vacation in Costa Rica, where I’m doing an ecologically-minded tour through the country to see wildlife. I have been having an absolutely amazing time and there are so many beautiful insects to be seen and identified. As a long time follower and fan of What’s That Bug, I thought I would submit one and see if you had any idea what it is (perhaps family/order/genus if not species). I have a lot of photos of bugs that have yet to be ID’d but I don’t know where to start with this one in particular. The bug was sighted in the Monteverde region and the photo was taken with a Canon 100mm f/2.8 macro lens. Thank you so much for your time and please keep up the excellent work!
PS: If you have any interest in seeing the other bug photos I have taken so far, I would be happy to share! I got a great shot of a bullet ant, among others.
Signature: Casey

Dear Casey,
Thanks for the compliment.  By all means submit more images, but please continue to use our standard form and please confine your submissions to one species per form unless there is a good reason to submit multiple species together.  This Fly in the order Diptera is a Robber Fly in the family Asilidae, but when we did a search for Asilidae Costa Rica, we did not find any matching images.  The closest we could find is this similar looking female Robber Fly from the UK.  Your individual appears to be a male judging by the claspers as the tip of his abdomen.  We suspect that there is much Robber Fly diversity in Costa Rica and we also suspect they are not as well documented as larger, flashier insects like butterflies, moths, beetles and katydids.  Here is a Costa Rican Robber Fly on Quaoar Power Zoo that is definitely NOT your species.  Robber Flies are adept predators that often take prey on the wing.

Letter 17 – Robber Fly

Subject: Big yellow fly
Location: Western NC
July 17, 2016 4:56 pm
Greetings to you: I studied some entomology in college and stay fascinated with all 6 and 8 legged creatures. Today this fly was menacing like bee flies are not. It was about 4cm in length. Any idea? A robber fly maybe?
Signature: Buzz in NC

No need to reply, I know now it’s a robber fly.
Thanks!

Dear Buzz in NC,
We know you wrote we didn’t need to reply, but we thought you might be curious if we were able to take the identification further than the Robber Fly family.  We are pretty certain this is one of the Bee-Like Robber Flies in the genus Laphria, and it looks like a pretty good match to the images of Laphria apila on BugGuide, but those images all represent a single individual from Florida.  Your individual appears to have more yellow on the abdomen, but that could represent variation within the species, or it might be a different species.  Your individual looks like this BugGuide image that includes this comment from Ben Coulter:  “The bald thorax with long fringe of hairs on the margin reminds me of apila. I hate to suggest it without good reason, but perhaps this is one of those oft-invoked undescribed species.”  Here is another BugGuide image that is unidentified, though there is some speculation it might be Laphria apila.

Letter 18 – Robber Fly:

Subject: Archilestris magnificus
Location: Palominas, Arizona
August 25, 2016 7:37 pm
I actually found out what this guy was from your website when I first photographed it in 2013. Haven’t seen it since, until yesterday. First photo from 2013, second from yesterday, 8/24/2016. They seem to like being photographed, quite the posers!
Signature: mtnrow

Dear mtnrow,
Thanks so much for providing us with documentation of two sightings of this magnificent Robber Fly, Archilestris magnificus, a species we first posted back in 2007.

Letter 19 – Probably Robber Fly

Subject: Flying “Bee” that eats flies…
Location: Pacific Northwest
October 4, 2016 5:34 am
The Pacific Northwest always seems to come up with tales of strange creatures…BigFoot, D.B Cooper, the Puget Sound Monster…and now a mysterious flying insect that feeds on flies.
I’ve witnessed this assassin do its work usually during the Summer months (actually, I’ve only seen it during the Summer months) and is most active during daylight hours.
It resembles a black and white bumble bee (the white almost exactly replacing the yellow areas of the common bee). Its predatory method is to hover around wherever there are flies, and amazingly will swoop down on top of a fly before the fly knows what hit it. After a few seconds, predator and prey fly off into the sunset.
But the assault is even more interesting. I bore witness to the process while these mysterious fly-eaters did their work on the sunny-side of my tent while camping in Oregon. The flies were congregating on the Western side of the tent, around 1pm, and there were a lot of them. Big and small (so I don’t know how many species there were). Out of no where a flight of these assasin bugs began hovering over the flies. They would swoop in and lans on top of their target. Then, as they allowed me close enough to witness, they spin the fly over and over as their pincers clip off their victim’s wings and legs before flying off with only the torso remaining. It was rather cool to see…there were many of the assassins, and over the course of an hour I witnessed a thousand legs and wing fall along the side of the tent.
I’ve seen these bugs from the Columbia River Gorge, to metropolitan Portland, OR, to the Oregon/Washington Coast.
(Apologies for no pictures, and it isn’t for lack of trying. I have tried many times, but those little buggers are pretty darn quick…and small.)
Signature: Please Bug Me

Though you did not provide an image, we found your letter highly entertaining, and we believe you observed one of the predatory Robber Flies that mimics a bee.  There is one species known as a Bee Killer in California, Mallophora fautrix, but we don’t know if it is also found in Oregon.  Another possibility is a Bee-Like Robber Fly, Laphria astur, that is found in Oregon and is pictured on BugGuide.  There are also many other possible species, but without an image, we do not want to speculate.

Letter 20 – Robber Fly

Subject: Mail truck invading bug in Massachusetts
Location: Reading, Massachusetts
July 29, 2017 7:04 am
So my boyfriend is a mail man in Massachusetts and he keeps getting invaded by these odd looking bugs. We’ve never seen them before but apparently all his mail man friends are having the same hitchhiker bugs in their trucks as well. Help what is it?!?!?
Signature: Mandy (singing mailmans gf)

Dear Mandy,
This is a Robber Fly in the family Asilidae, an aerial predator that catches its prey while on the wing.  We are unable to provide a species identification.  We don’t know why all the mail trucks in Reading, Massachusetts are being used by the Robber Flies as resting spots.

Letter 21 – Robber Fly

Subject: Robber Fly species ID please?
Location: Merrimac MA
July 30, 2017 8:07 pm
Hello,
Attached is a photo of a Robber Fly in our yard in Merrimac, Massachusetts in July, 2017. We would like to know what species it is. We had never seen one before, but we are only about 30 minutes from Reading, MA where evidently the mail trucks seem to be a favored spot to hitchhike!
Thank you!
Signature: Bonnie

Dear Bonnie,
This looks to us like a male Efferia aestuans, and according to BugGuide: “The most likely robber fly to land on humans.”

Letter 22 – Robber Fly

Subject:  identify flying insect
Geographic location of the bug:  cape town, south africa
Date: 01/04/2018
Time: 03:05 AM EDT
Is this a wasp or is it a non-stinging insect?
How you want your letter signed:  APPLE COHEN

Dear Apple,
This is not a Wasp and it is a non-stinging insect.  This is a predatory Robber Fly in the family Asilidae, and it reminds us of the North American genus known as the Hanging Thieves because after catching winged prey, including stinging wasps and bees, the Hanging Thief feeds by sucking vital fluids from the prey while hanging from a single leg.  Flies bite, they do not sting.  While we believe there is little chance of a person being bitten by a Robber Fly in most situations, attempting to handle a Robber Fly might result in a bite.

Letter 23 – Robber Fly

Subject:  What’s this bug?
Geographic location of the bug:  Colorado
Date: 06/22/2018
Time: 09:31 AM EDT
Your letter to the bugman:  Hi,
I saw this on my security camera and I’m just curious to know what it is.
How you want your letter signed:  Curious

Dear Curious,
This is most definitely a predatory Robber Fly in the family Asilidae, and it looks to us, based on images posted to BugGuide, that it might be a member of the genus Saropogon.  According to BugGuide:  “20 spp. in our area” and the sighting map includes most of the American Southwest.

Letter 24 – Robber Fly

Subject:  Silver, winged insect with bristly legs
Geographic location of the bug:  Amesbury, MA
Date: 06/27/2018
Time: 10:42 PM EDT
Your letter to the bugman:  Hello! I love your site and thought this bug was fascinating as I’ve not yet seen it nor have a few folks I showed the picture to. The body appeared to be silver and black and the bristled legs each had a pincer at the end. The bug didn’t seem aggressive as I got close, but definitely had a tough appearance. Any ideas to what it could be?
How you want your letter signed:  AJ

Dear AJ,
This is a beneficial, predatory Robber Fly, and based on this BugGuide image, it might be Efferia aestuans or a closely related species.

Letter 25 – Unknown Robber Fly

Subject:  Unidentifiable Bug
Geographic location of the bug:  South Central PA
Date: 06/29/2019
Time: 08:31 PM EDT
Your letter to the bugman:  No one seems to know what this bug is.
How you want your letter signed:  Mary Brady

Dear Mary,
This is a predatory Robber Fly in the family Asilidae, and we thought it would be much easier to provide you with a species identification, but we are still uncertain regarding its identity.  It reminds us very much of  Microstylum morosum which is pictured on BugGuide, but that species is only reported as far east as Missouri on BugGuide.  We will continue to research this matter.  How large was this individual?

Eric Eaton responds after we ask his input.
Daniel:
I got nothin’, sorry.  I would agree with your initial diagnosis, though.  I wonder if there is more to the story?
Eric

Letter 26 – Unidentified Large Robber Fly

Subject:  What is this thing?
Geographic location of the bug:  North Carolina
Date: 08/15/2019
Time: 11:37 AM EDT
Your letter to the bugman:  Hello, recently I found this very strange looking…wasp? Hornet? I don’t know. It was dead when I found it. I tried searching for what it might be online but couldn’t find anything with a matching description. I hope you can help!! Thank you.
How you want your letter signed:  Mack

Dear Mack,
This is a large, predatory Robber Fly in the family Asilidae, but we do not recognize the species.  The black coloration is quite unusual for an eastern species.  It might be Proctacanthus nigriventris which is pictured on BugGuide.  Your dorsal, lateral and frontal views are excellent for an expert’s ability to identify the genus and species, but alas, we do not possess that expertise.  Perhaps one of our readers will provide a less general identification.