Mydas Flies Facts: Uncovering the Secrets of These Unique Insects

Mydas flies are fascinating insects known for their large size and striking resemblance to wasps. They can be found in various parts of North America and are often considered beneficial due to their predatory nature during their larval stage. These eye-catching insects have jet-black bodies with smoky wings, often sporting bright orange markings on their second abdominal segment, making them quite noticeable in nature.

These insects spend a significant portion of their life underground as larvae, feeding on soil-dwelling insects such as grubs. When they pupate, they use specialized spines to move up to the soil’s surface before emerging as adults. Adult mydas flies have a more ambiguous diet, with debate surrounding whether they maintain their predatory habits or shift to nectar-feeding.

Although they may appear intimidating due to their size and appearance, mydas flies are in fact harmless to humans. Their striking looks and unique life cycle provide an interesting subject for entomologists and nature enthusiasts alike, making them a captivating topic for those interested in learning more about the world of insects.

Mydas Flies Overview

Family Mydidae

Mydas flies belong to the family Mydidae and are known for their medium to large size and wasp-like appearance. They have long, clubbed antennae and display a distinctive pattern of curved cells in their wing venation¹. Some key features of Mydas flies include:

• Medium to large size
• Wasp mimicry
• Clubbed antennae
• Curved cells in wing venation

Order Diptera

As members of the order Diptera, Mydas flies are classified as true flies. As true flies, they possess only one pair of wings². Key characteristics of Diptera include:

• One pair of wings
• Short antennae (in most species)

Class Insecta

Mydas flies fall under the class Insecta, which comprises all insects. Insects are characterized by having:

• Three pairs of legs
• A three-part body (head, thorax, and abdomen)
• Usually one or two pairs of wings³

Phylum Arthropoda

Insects, including Mydas flies, belong to the phylum Arthropoda. This phylum is home to the largest group of animals on Earth and includes animals such as insects, spiders, and crustaceans. Arthropods are characterized by:

• Exoskeleton made of chitin
• Segmented body
• Jointed appendages⁴

Kingdom Animalia

Finally, Mydas flies are part of the kingdom Animalia, which encompasses all animals. Key features of Animalia include:

• Multicellular, eukaryotic organisms
• Heterotrophic (obtain food by consuming other organisms) life forms
• No cell walls⁵

Physical Characteristics

Size and Length

Mydas flies are known for their large size, typically measuring between 1.0 to 1.5 inches in length. To put this into perspective, they often resemble wasp species like the spider wasps of the family Pompilidae.

Colors and Patterns

These flies display an interesting variety of colors and patterns, such as:

• Black
• Dark
• Tan
• Red
• Orange
• Yellow

Some species even have an attractive combination of these colors in the form of bands, making them stand out visually.

Winged Adult Features

The adult Mydas flies exhibit remarkable features that set them apart from other flies:

• Two wings: Like all true flies, Mydas flies have just one pair of wings. This is a distinguishing characteristic when comparing them to other insects with more than two wings.
• Clubbed antennae: Unlike most flies, Mydas flies possess clubbed antennae, similar to those found in butterflies. This unique feature can serve as an identifier when trying to distinguish them from other fly species.
• Wing venation: Mydas flies’ wings exhibit a distinctive venation pattern, adding to their overall intriguing appearance.

To help visualize the differences between Mydas flies and other fly species, here’s a comparison table:

Behavior and Habitat

Diet and Feeding Preferences

Mydas flies adults are known to feed on nectar, flowers, and pollen. They mostly prefer white flowers with open structures that provide easy access to nectar sources:

• Nectar
• Flowers
• Pollen

For example, flies are attracted to plants like rattlesnake master in gardens. Mydas fly larvae, on the other hand, act as predators and feed on grubs of beetles in soil and rotting wood, providing biological control of pests.

Mating and Reproduction

Limited information on mating and reproduction of Mydas flies is available from the search results provided.

Range and Distribution

Mydas flies inhabit various environments across North America, including tropical, subtropical, and dry regions:

• Tropical forests
• Subtropical grasslands
• Woodlands
• Meadows
• Prairies
• Desert Southwest and dry areas, such as Sonoran Desert summer

Below is a comparison table of some habitats where Mydas flies are found:

Mydas flies are considered wasp mimics, also known as Batesian mimicry. This means they resemble wasps, which helps deter predators, but they are actually harmless. Their role in conservation includes their predatory nature, helping control pest populations, and their involvement in pollination as they visit flowers in search of food sources.

Life Cycle and Development

Egg

Mydas flies, like other insects, start their life as eggs. The female lays eggs, and when they hatch, grublike larvae emerge. These larvae have the primary objectives of eating and growing during this stage in their life cycle.

Larval Stage

The larval stage is vital for the development of Mydas flies, as they spend most of their lives in this stage. It’s common for Mydas flies to spend at least a year as a larva, during which they molt several times.

• Early instars feed on beetle grubs
• Late instars switch to a more armored source like prey eggs

A well-known Mydas fly is the Mydas clavatus. Their larvae are known for feeding on beetle grubs, helping to control beetle populations in the environment.

Pupal Stage

When a Mydas fly larva is ready to transform, it undergoes the pupal stage. The pupa is the stage where the insect metamorphoses into an adult Mydas fly. The duration of the pupal stage varies depending on environmental conditions and species.

Adult Stage

During the adult stage of the Mydas fly life cycle, they focus mainly on reproduction. Adult Mydas flies resemble wasps, but they are harmless. They typically have darker colors like black, dark, or tan, with red, orange, or yellow bands. Like all true flies, they have only one pair of wings and clubbed antennae.

Characteristics of Adult Mydas Flies:

• One pair of wings
• Clubbed antennae, similar to butterflies
• Wasp-like appearance, but harmless

In conclusion, the life cycle of the Mydas flies consists of the egg, larval, pupal, and adult stages. Mydas clavatus, a well-known Mydas fly, helps control beetle populations, providing essential ecological benefits. Their unique wasp-like appearance, clubbed antennae, and roles in their environment make them fascinating subjects to study.

Interactions and Relationships

Batesian Mimicry

Mydas flies exhibit Batesian mimicry, which means they resemble wasps in appearance, but they are actually harmless. This helps protect them from potential predators that would be deterred by a dangerous-looking insect. They often have black, dark, or tan bodies with red, orange, or yellow bands.

Predators and Prey

• Larvae: Mydas fly larvae are predators of soil-dwelling insects, such as beetle grubs found in soil and decaying wood. Due to their feeding habits, they have been proposed as a biocontrol agent for sod farms to control root-eating beetle grubs that can damage lawns.

• Adults: There is debate regarding the feeding habits of adult Mydas flies. Some scientists believe they may continue to be predators, while others suggest they might be nectar feeders.

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 – Mydas Fly

peach borer or mimic?
Location: powhatan county, virginia
June 17, 2011 10:22 am
there is a low-cut, decomposing stump in my flower bed, from a tree felled many years ago (hardwood, not fruit). when tending the flowers, i noticed and collected this insect, as well as several pupae cases (from which another like insect was emerging), from around the base of the stump on june 16, 2011.
i am not convinced it is a peach borer, because the antennae are very different, as are the eyes/head – more fly-like. the orange band is higher up on the abdomen, and the wings at rest fold over one another. i’m fairly certain it has only one set of wings. any info would be appreciated!
Signature: bugwatcher

Hi bugwatcher,
This incredible creature is a Mydas Fly, Mydas clavatus, and according to BugGuide, it is a:  “Large black fly with red/orange mark on top (dorsum) of 2nd abdominal segment. Body hairless, cylindrical. Eyes large. Antennae are distinctively clubbed in the Mydidae. This species flies rather boldly in the open. With the black-and-orange pattern, it resembles a wasp and fools the casual observer.”  The larvae live in compost piles, soil and rotting wood where they feed on June Beetle Larvae.  According to BugGuide:  “Eggs are laid singly in soil or rotting wood. (See video of oviposition–Flickr). Mydas larvae prey on beetle larvae, esp. those of June beetles. Larvae pupate close to soil (or wood?) surface. Adults are active only in mid-summer. Mating system in this species unknown.”  You are observant in noticing that the Mydas Fly, in addition to mimicking Spider Wasps, looks very similar to a female Peach Tree Borer.  The Peach Tree Borers are also wasp mimics, as you can see in this photo from our archives.

thank you so much. the more i talked about fly characteristics, i looked up all the flies on your site, and found Mydas after i had sent my email. i was thrilled to discover what it was, and promptly let it go. a beautiful fly, and a garden helper at that. when it flies, it has a very nice low buzz, also wasp-like and intimidating. i feel fortunate to have been able to examine it so closely during it’s brief adult stage. thank you again for your prompt response and devotion to the site.

Letter 2 – Mydas Fly

Large Wasp in AZ
Location: Tuwhicson, AZ
June 24, 2011 8:52 pm
Hello,
I took this picture of this huge wasp-type insect in Tucson, AZ and I’ve been trying to figure out what it is. It was maybe about 1.5” – 2” in length. The closest-resembling thing I’ve been able to find is the tarantula hawk, but I’ve only read about those having black abdomens/bodies with orange wings. Can you please identify my bug?? Thanks!!
Best,
Brooke
Signature: Brooke

Hi Brooke,
This is not a Wasp.  At first we thought it might be a Robber Fly, and we found a Robber Fly from Arizona on BugGuide, Archilestris magnificus, that is colored similarly, but alas, the antennae are quite different.  We then shifted to what our first impression was, that this might be a Mydas Fly, and we found a photo from Colorado on BugGuide of Phyllomydas phyllocerus  which matches quite nicely.  Additionally, there is a nice closeup of a related individual from Florida on BugGuide that also looks close.  We cannot say for certain that either the genus or species is correct, but we are relatively certain that this is in fact a Mydas Fly.

Hi Daniel,
Thanks for your help and your quick response!!!  Your website is excellent.  I started thinking after I posted my photo that it might be a fly because of the trumpet-shaped thing coming out of its face/mouth – or whatever flies bite/suck with.  I’m not up on my insect terminology.  That is one huge fly!  I’m relieved to know that it’s not a tarantula hawk.
Thanks again,
Brooke

Hi Brooke,
You are correct that wasps and flies have very different mouth anatomies.  Flies have a proboscis designed for sucking up food, and wasps have mandibles for chewing food.  Here is how the Utah Education Network website describes the mouth of a fly:  “Flies cannot chew. They have to suck up their food. Flies have mouth parts that absorb food like a sponge. Their food has to be in a liquid form in order for them to eat it. They have a tongue shaped like a drinking straw to slurp up their meals. Flies that eat nectar or blood do so by using their tongue which is called a proboscis. Even flies that eat other insects do so by sucking out the insides of their victims.”

Eric Eaton confirms ID
Daniel:
Sure looks like a Mydas sp. to me.  Nice detective work!
Eric

Letter 3 – Mydas Fly

Massive Black Winged Thing
Location: South West Michigan
July 13, 2011 9:53 pm
This afternoon (July 13th) I was sitting outside around 4 pm when this really big insect landed on the mint in my garden. I thought it looked wasp-like on top, but the bottom looks more dragonfly-ish. It flew off after a bit and when it came towards me I ran. In my defence; it was over an inch long and looks rather badass.
I’ve asked several people but nobody knows! Any ideas? Thank you!
Signature: Erica

Hi Erica,
The Mydas Fly, Mydas clavatus, is actually a true Fly, though it does mimic certain wasps as a defense mechanism.  It does not bite or sting, and despite its large size and fierce appearance, it is perfectly harmless.

Letter 4 – Mydas Fly

large black fly(?)
Mon, May 4, 2009 at 10:36 AM
Found on tomato plant 5-4-09, in South-central Texas. it is relatively large – more than 1 inch, at least. As the photos indicate, there is a faint light circle near the tips of the upper wings. Also, a bi-color spot (orange and buff) on each side of the abdomen near where it joins the thorax. The antennae are very prominent with black, white, and gray bands, and the head (which looks like mostly eyes) protrudes from the thorax on a small “neck”. It was not moving around very vigorously, perhaps newly hatched from compost or looking for a place to lay eggs. . .
mmcg
Comal County, Texas

Dear mmcg,
This is a Mydas Fly, probably Mydas clavatus. There are many great photos posted on BugGuide. Despite its wasplike appearance, the Mydas Fly will not sting nor bite humans. There are conflicting sources that claim it is predatory, and there are other sources that claim that males take nectar. Your compost theory is a good one since larvae live in rotting wood or soil where they prey on beetle larvae.

Thank you very much for the helpful i.d. and reply.
How could I have searched BugGuide more effectively to find the photos
and i.d. already there? I tried browsing images of two or three
subgroups under the diptera order, but there are just too many for that
to be a satisfactory search strategy.
I am an amateur naturalist, working on preparing a guide to wildscaping
Hill Country homes and farms, highlighting the native plants of our 7
acres, together with photo-illustrated lists of birds, reptiles &
amphibians, mammals, butterflies and moths, plus some of the
more-interesting other insects found here.
Predictably, the insect identification part is the hardest! I have
really appreciated your website as a resource, though.
Meredith McGuire, Professor of Sociology and Anthropology, Trinity
University

Dear Meredith,
Good luck with your project.  We frequently begin by browsing in BugGuide.  There is a Browse option when you select an order, family or genus, so it is a really good way to narrow your search.  We have to admit that we often spend many fruitless searches on BugGuide, and then when we finally arrive at the answer, it seems so obvious.

Letter 5 – Mydas Fly

What’s this bug?
Location: Lake Texoma, Oklahoma
June 28, 2011 10:41 pm
My son took this picture of this bug on the shores of Lake Texoma, on the Oklahoma side, the weekend of June 25 of this year.
It’s rather large, maybe 2in. long and flies.
I cannot find it in your extensive library, which is impressive and very helpful.I wasn’t even sure what ”type” of insect to start the search. Didn’t find it under ”wasps” or ”bees” or ”flies”.
Help!
Signature: A. Gordon

Dear A. Gordon,
We admit that our vast archive can be quite daunting if you don’t know where to start.  This is a Mydas Fly, Mydas clavatus, and it is an excellent mimic of Spider Wasps in the family Pompilidae.  Once we lightened your photo a bit, the detail in the head and body was really revealed.

Letter 6 – Mydas Fly

Huge Fly!
I just discovered your site because I was trying to identify a giant fly that we discovered yesterday in our fireplace. Nice site! Thankfully, this fly was behind the doors of the fireplace. It was in the around 90F yesterday so he didn’t live long in there and I got a chance to photo him today. I don’t keep the flu open, so I’m trying to figure out how he got in there. I do not see any flies on your site that look like this one. Attached are three photos. Hopefully the ‘perspective’ photo gives you an idea of his size.
Chris
by the way, I am in New Jersey.

Hi Chris,
Because of the large size and the clubbed antennae, we believe this to be a Mydas Fly in the Family Mydidae. Adults are predatory, feeding on caterpillars, flies, bees and Hemipterans. Though we are 99% sure this is a Mydas Fly, we are checking with Eric Eaton for a second opinion.

Ed. Note: Here is Eric Eaton’s quick response.
“That certainly is a mydas fly! Is the image in black and white? If so, it could be Mydas tibialis, which has no red band like M. clavatus, but has orange legs on a dark brown/black body. Mydas flies seem to be attracted to large, standing, hollow trees, so it might have mistaken the chimney for a tree and flown in. Flues do not close tightly enough to exclude insects is my bet, and so the thing made it all the way to the fireplace. They sure are intimidating, the loud droning buzz alone being quite ominous! Luckily they are harmless to people. Eric ”

Letter 7 – Mydas Fly

Mydas clavatus – Mydas Fly
Mon, Jul 6, 2009 at 1:59 PM
I know you have some pictures of this already but I can’t help but send this to you anyway. I found this on my blooming mint plants today and thought it was a huge wasp. A search on bugguide showed me that it was instead one of the largest flies in the US a mydas fly. Looks like it must be a male as they say females don’t feed on nectar. He is jet black with a brilliant orange stripe on the upper abdomen with Iridescent wings. Looked to be about 1 1/2 inches in length. Not aggressive but focused on nectar gathering.
Surely is an amazingly beautiful creature!
Stefanie
Paducah, KY

Hi Stefanie,
Thank you for sending us your gorgeous Mydas Fly images.  We will link to the BugGuide page for our readers who want more information on this spectacular insect.

Letter 8 – Mydas Fly

What is this bug?
June 14, 2010
This guy has been around the yard a couple times now. Pretty good size, maybe 1-1/2″ or so, jet black except for an orange band around it’s abdomen.
Thanks, Ben Hanson
Port Charlotte Florida

Hi Ben,
We received an email from you on May 21, and we posted your photo of a Mydas Fly.  This is another view of the same species of Mydas Fly, Mydas clavatus.  We apologize if we did not write back to you directly, but your previous letter has been on our site since then.  We are postdating this letter to post live to our site during our absence in the coming week so that our readership will continue to get daily updates.

Daniel;
Thanks so much for the reply and information! I might have missed an earlier reply…
Thank you people for what you do. Your site and Facebook page is very highly entertaining and informative!
Ben

Letter 9 – Mydas Fly

Black Robber Fly ?
July 15, 2009
This is a common fly in my garden this summer. There may be as many as five of them that have set up territories throughout my strawberries, squash, and tomatoes. It resembles a robber fly in the way it perches on vantage points and quickly flies away when disturbed in the slightest. It sometimes seems aggressive and will even investigate me when I attempt to photograph it. This is a large black fly that I suspect is over an inch in length and has orange, lateral, very round, spots, one on either side of the abdomen near the thorax. Some of the individuals have light yellow spots and others have brighter orange spots. I have never seen one with prey, as I do the other recognizable species of robber flies in the garden. This picture was taken in mid-July during some of the hottest days of summer in Oklahoma. Rain has been sparse and the ground is very dry except around the garden that is regularly watered and attracts several species of insect.
K. Hopkins
Oklahoma, USA

Dear K.,
This is a Mydas Fly, Mydas clavatus.  According to BugGuide:  “I have seen adults (males?) of this species taking nectar from several sources in Durham, North Carolina. I have seen a female ovipositing in a dead maple stump. Later, I found this stump was full of carpenter ants and large beetle larvae (probably Odontoaenius disjunctus). I have not observed the adults taking prey on the wing. Sources vary on the feeding habits of adults. Most say the adults are predatory, but this may be incorrect. Perhaps this is due to confusion with the somewhat similar Robber Flies (Asilidae)?” BugGuide also indicates that male Mydas Flies engage in Hilltopping, which Wikipedia explains as a mate-location behavior where “Males of many butterfly species may be found flying up to and staying on a hilltop – for days on end if necessary. Females, desirous of mating, fly up the hill. Males dash around the top, competing for the best part of the area – usually the very top; as the male with the best territory at the top of the hill would have the best chance of mating with the occasional female, who knows the ‘top male’ must be strong and thus genetically fit. Many authors consider this as a form of lekking behaviour.[4] Many butterfly species including swallowtails, nymphalids, metal-marks and lycaenids are known to hill-top.”

Letter 10 – Mydas Fly

???
Dear Bug Folk (or bug-knowledgable artists),
Hope you’re still answering queries. What’s my bug? Almost a blue iridescent tinge to the body in bright sun. A little scary!!
Thanks, Sue Lenaerts

Hi Sue,
Mydas Flies are harmless, but we were unfamiliar with this species with orange legs and antennae. Searching BugGuide led us to Mydas tibialis.

Letter 11 – Mydas Fly

Wasp ID
I found this "wasp" or hornet making a nest in an old stump in Connecticut. It was a hot day and there were many of them. What kind is it?
Gary

Hi Gary,
This is not a wasp, but a Mydas Fly. Mydas Flies are often mistaken for wasps. According to our Audubon Guide: “The slender larvae, which reach 1 1/2″ (38mm) when fully grown, live in soil or rotting wood and prey on beetle larvae.” The nest building you thought you observed has two possible explanations in our minds, though the two explanations might be combined. You might have seen a mass emergence of adults from their larval home after metamorphosis or you might have seen a congregation of mating adults laying eggs where the larvae will have a ready food source. You might even have seen the mass emergence of adults and the subsequent mating, with the next generation occupying the ancestral home. Adult flies eat caterpillars, bees, other flies and hemipterans.

Thanks for the info. Dan. I’m not an entomologist, but have a strong interest in nature an photography. My old maple stump (about 1 m. in diameter and dead about 7 years has been a great source of amusement. Every year some new mammal, fungus or group of insects appear!) Keep up your good service to curious people.
Gary

Letter 12 – Bald Faced Hornet decapitates Golden Legged Mydas Fly

mydas vs. hornet
Location: Northern Indiana
August 25, 2011 10:21 am
This is not an ID request, but thought that other WTB addicts might appreciate it. This picture is not great quality, but here’s a link to the full video of a hornet attacking and decapitating a golden-legged mydas fly:
http://www.facebook.com/rumvillage#!/video/video.php?v=207796845940579&oid=116718851680137&comments
Signature: Vince

Hi Vince,
We were unsuccessful in locating a Golden Legged Mydas Fly online, but we did find Mydas tibialis on BugGuide.  It is a species with no common name listed and it has been reported from Indiana.  Your Food Chain image is wonderful.  We wonder if the best Hornet hunters decapitate large and dangerous prey like Dragonflies, and then they communicate to the hive where to find the kill.

Letter 13 – Mydas Fly Drowns in Pool

Subject: wasp? bee? hornet?
Location: Whitewater, California
June 7, 2016 10:02 am
Hello!
My kids and I normally play bee rescue in our pool. We live just outside Palm Springs, CA so there is not much water just laying about so bees love our pool, sadly a lot of them hit the water and almost drown so we will fish them out and let them dry off before they decide to go on their way.
However, the other day after lunch we found this poor thing in the pool, we didn’t get to it in time since we were in the house.
Although, I am a bit nervous as to what it is because it was so much bigger! It was about 1 1/2 -2 inches long!! Huge compared to our little bees. Can you tell me if this one is safe to save and what it is? I have looked through your site and can’t find anything like it.
Thank you so much for your help!!
Signature: Cristena

Dear Christena,
None of the above.  This is a Mydas Fly in the family Mydidae, but it does not look like any species we have seen.  We cannot even locate a conclusive match on BugGuide, but our best guess is that it is in the genus Nemomydas like this unidentified species on BugGuide or this Nemomydas venosus also pictured on BugGuide.  Neither image looks exact, but they are close enough for us to guess your individual is closely related.  According to BugGuide, Mydas Flies are:  “Large flies, often wasp mimics. Have prominent, clubbed antennae and distinctive wing venation” and to the best of our knowledge, they are perfectly harmless.  As an aside, it is not possible to make out the head of the Mydas Fly in your image as it is partially obscured by the wings and body of a smaller fly.

Letter 14 – Mydas Fly drowns in pool

Subject:  Fly? Wasp?
Geographic location of the bug:  Northwest Indiana
Date: 07/07/2020
Time: 09:14 PM EDT
Your letter to the bugman:  Hi! We found this fella floating in our pool. I have lived here all my life and have never seen a fly/wasp this big! Can you identify?
How you want your letter signed:  Carrie

Dear Carrie,
This is a harmless Mydas Fly, and it is widely believed that this Mydas Fly, Mydas clavatus, benefits from mimicking a stinging wasp.