Currently viewing the category: "Bot Flies"

Subject: Is this a Bumble Bee?
Location: Central New Hampshire
July 20, 2013 4:28 pm
Black and white markings, about the size of a Bumble Bee. Have never seen a bee
quite like this. It was very near a DogWood Tree in our yard.
Signature: Psquare

Bot Fly

Bot Fly

Dear Psquare,
It is easy to mistake this Bot Fly for a Bumble Bee.  Bot Flies are true flies and they are parasitic in the larval form, and according to BugGuide:  “The larvae are subcutaneous (under the skin) parasites of the host. Their presence is easily detected as a tumor-like bulge, often in the throat or neck or flanks of the host. The larvae breathe by everting the anal spiracles out a hole (so they are oriented head-down inside the host). They feed on the flesh of the host, but only rarely does the host die as a result.”  We are going to copy Jeff Boettner in our response in the hope that he can identify the species of Bot Fly you have photographed.

Hi Daniel and Psquare,
Your bot fly is a Cuterebra fontinella fontinella bot. This bot is a parasite of white footed mice, Peromyscus leucopus. Its a little hard to see the key features (a side view is helpful) but there are only a handful of bots in NH and this is the most common bot in your area. The other bots have either red eyes (rabbit bots) or more white or yellow on their backs. So I am confident of this ID. By the distance between the eyes, this one is a female.
Thanks for the post.
Jeff Boettner

Subject: Parasitic Larva
Location: Chihuahuan Desert, Far West Texas near the Rio Grande
April 19, 2013 4:01 pm
Hi there! This morning I set out to doctor what I thought was an infected thorn stuck in my dog’s side. Imagine my shock when instead of a thorn, I pulled out a wiggling larva! It didn’t look like a normal fly maggot to me, and a quick search of the internet pointed me to the Bot Fly. I’d really appreciate your expertise to clear up this baby bug’s identity.
Signature: Sara

Bot Fly Larva

Bot Fly Larva

Hi Sara,
We are really happy you identified your dog’s Bot Fly Larva, and even though they are allegedly not a threat to the health of the host, your dog is probably relieved to have had it removed.

Name that larvae
location:  New York
September 15, 2012:  6:07 PM
A friend of mine’s daughter had a bite on her chin a few weeks ago and the pediatrician said it was a spider bite. Last week there appeared to be a hole in her skin. And today, this came out. What is it???
Christie Mierzwa

Bot Fly Larva

Hi Christie,
This appears to be a Bot Fly Larva.  You did not use our regular submission form and there is no location listed for your sighting.  Please provide us with a location.  Your verbal description fits what one would expect of a Bot Fly, though in North America, the typical hosts are rodents.  We will try to copy Jeff Boettner to see if he can provide any insight.

Thank you. I used an old email address from a few years back and did not know there was a submission form. We live in NY. In this case, the host was a 3 yr old child!!

Thanks for the update Christie.  We eagerly await input from Jeff Boettner.

Subject: Giant Fly
Location: Denver, Colorado
July 7, 2012 12:21 pm
Found this thing outside on the patio, it’s wings were incredibly small/shriveled when we found it, but have grown a lot by now. What in the world is it?! Looks like some kind of giant fly…but could it be a horse fly? The eyes aren’t together so it doesn’t seem like it. Thanks!
Signature: Thanks!

Newly Metamorposed Rabbit Bot Fly

Your insect is a freshly metamorphosed Bot Fly in the genus Cuterebra.  Both the wrinkled wings and the protrusion on the face indicate the recent eclosion.  Jeff Boettner provided this information for a recent posting:  “The one you photographed is very freshly emerged, the wierd face is from a balloon like structure that inflates to help push the fly out of the pupal case, and then it gets reabsorbed back into the face.”  We will copy Jeff on this response to see if he is able to provide any additional information.

Jeff Boettner responds
Hi Daniel and Tyler,
Your bot looks like Cuterebra lepusculi, a rabbit botfly. They are a little tricky to ID until they have been alive for a day or two, yours is freshly emerged. If you keep it around for a few days the face will be helpful to see as well as the pattern on the hind end. Bots do not feed as adults, so are easy to hang onto them, although they only live for about 10 days. Their goal is to find a mate and then infect rabbits.
I am doing dna work on reworking the botflies, and would love to get this as a specimen, if you are willing to part with it? We are working on a National Science Foundation grant proposal, and rabbit bots are difficult to get. I would put the specimen in the Smithsonian collection when I am done with it. We use part of one leg for dna work, which we fresh freeze to -80C until we do the sequencing. We hope to look at the evolution of botflies and their hosts. This work will also go toward making a better field key to better help identify bots.
I am happy to cover your shipping costs. Can be shipped live or dead in a pill bottle, if dead add some tissue to bottom and top to prevent bot from moving a lot in shipment.
My address
Jeff Boettner
Plant, Soil and Insect Sciences
Room 115 Ag. Eng. Bld.
250 Natural Resources Road
Amherst, MA 01003

Nice post. Daniel does a great job with whatsthatbug! I learn a lot from the site. Keep up the great work.

Update from Jeff Boettner
July 17, 2012
Hi Tyler (cc’ing Daniel)
Just to let you know the bot arrived in excellent condition. It is a female Cuterebra lepusculi for sure, which is a rabbit bot. It uses cottontail rabbits as a host, (mostly Sylvilagus audubonii and Sylvilagus nuttallii as hosts in your area).
Thanks so much for sharing it. I will freeze a leg and use it for our next dna run. A tough one for me to find. Will add the bot to our collection which will head to the Smithsonian collection eventually.
Tyler I will drop a check to you to cover your postage and time.
Daniel, I just did a donation to whatsthatbug too, for calling this (and other bots) to my attention. A huge help for our study. Keep up the great web site.
Thanks to you both. Keep on hunting and id’ing
Note: They just killed off our Plant, Soil and Insect Sciences Dept. So I am now officially in Dept. of Environmental Conservation. We HAD the oldest Ent Dept in the country. Otherwise I have the same address and email for now.
Jeff Boettner
Dept of Environmental Conservation

Hi Jeff,
We are horrified to learn that the oldest entomology department in the country is now defunct, and it doesn’t seem like a timely move since there appears to be more and more interest in insects since we began writing this online column back in 1999 on the now defunct American Homebody website after the zine American Homebody went online.  That was very kind of you to make a donation to WTB?  We will continue to notify you whenever a Bot Fly is submitted for posting or identification.  What is the peak season for Bot Flies.  We can make a nice featured posting at that time recommending people to send you specimens or at least to contact you.

Another Update from Jeff
Hi Daniel,
Bots are very random and hard to predict. Generally the bulk of bot reports come in starting with some western bots in April to bots from all over in July-August, then back to western bots in Sept-Oct. So I think it would be hard to time a write up. Luckily these guys are big so they tend to draw attention. And rabbit bots with their red eyes tend to get over reported, in spite of the fact that- in the wild- they are quite hard to find. So really neat to see what turns up on your site and BugGuide. Between the two of you, I have seen about 1/3 of all the bots show up, including the really rare C. mirabilis ( the male has still never been seen, and the female on BugGuide is only the 3rd specimen known in the world), and C. bajensis (which I got a specimen via BugGuide) and only known from about 15 specimens in the world. I got a specimen and dna from the second one, the first one above I flew out to New Mexico to talk to the family that found it –it had been buried in their yard by their kid- with a flower funeral- I would have put it in the Smithsonian :). We found the host rabbits in the area and I hope to work with a couple of rabbit biologists to try to find bots to rear out a male so it can be described in the near future. So I am having fun with even the random bots that show up.
I am thinking about doing a write up for American Entomologist telling about the value of both your site and BugGuide. I have had a ton of fun stories about doing this quest for bots. Last year I had an 8 year old post a male C. lepusculi (the same species of rabbit bot you just got me) from Texas. He just started collecting insects and didn’t want to part with it. I negotiated a deal with his dad to get him some BioQuip equipment in exchange for the bot. A few days later a 7 year old found the female also in Texas. So I did the same deal. Turned out the kids lived about 8 miles apart so I connected them so they could go collecting together. Fun. That bot is pretty tricky to find in the wild, I have never seen this species in the wild, but now have 3 for our work thanks to you guys. We sequenced the dna from the first two bots from TX and this was used in part of a proposal we wrote to the National Science Foundation to try to get funding to do more extensive dna work. We made the first cut, and now are trying to write a full proposal (due in August). It may take us a few years to pull off a working grant, but this would allow us to do 454 sequencing (which is current state of the art), but costs about $400 a fly to run. But each fly we can do will get us a bit closer to understanding both fly and mammal evolution. So cross your fingers!
So for now, this is working great for me. Bots are very hard to set out to look for them. Although I have thought about taking out an add in New Mexico newspapers (like a wanted poster) to try to have people watch for C. mirabilis in and around Albuquerque, NM during the middle two weeks of Sept. All three known specimens showed up within about 30 miles of this area during that time. I have spent about 10 days hunting for it so far. Keeps me off the streets.
Thanks for your concern about the Dept. We will still have some entomologists shifting to the Stockbridge School of Agric (within UMASS). But was a big surprise to all of us that they would break up PSIS. (they merged entomology and plant and soil sciences about a decade ago to try to save ent, but now have pretty much killed it off with this move). The current profs will stil be around, but the plan is to not rehire when this batch retires, and about 1/2 are already within a few years of retirement age. So not looking good.
I agree, it is crazy given we are seeing about 3 new insect species every year in Massachusetts alone. And soon no one to work on them. And meanwhile emerald ash borer is now about 30 miles from our MA border, and Sirex wood wasp is also in NY…crazy to name a few.

Subject: Weird, weird fly in Wisconsin.
Location: Wisconsin, USA
June 25, 2012 3:24 pm
Hi there,
Do you have any idea what the heck this is? I found it in my window — it’s about 1” long, very hefty. Apparently dipteran. This creature has a weird thing sticking out of the front of its head (mouthparts? emerging parasite?) and a couple of black upright ”fins” on its back just forward of the wing bases.
I’m an amateur entomologist and I’ve never seen the likes of this blighter before.
Thanks, and I’m interested in what you come up with!
Best wishes,
Signature: Rhian

Bot Fly

Dear Rhian,
This is some species of Rodent Bot Fly in the genus
Cuterebra.  Bot Flies are parasitic flies.  BugGuideprovides this graphic description of their life cycle:  “Females typically deposit eggs in the burrows and “runs” of rodent or rabbit hosts. A warm body passing by the eggs causes them to hatch almost instantly and the larvae glom onto the host. The larvae are subcutaneous (under the skin) parasites of the host. Their presence is easily detected as a tumor-like bulge, often in the throat or neck or flanks of the host. The larvae breathe by everting the anal spiracles out a hole (so they are oriented head-down inside the host). They feed on the flesh of the host, but only rarely does the host die as a result.”  We are copying Jeff Boettner to see if he is able to provide a species identification for us.

Bot Fly

Dear Daniel,
Thanks very much for the I.D. on that peculiar creature! The pictures in the link you sent look exactly like it, right down to the “fins” on the back (which I suppose are some kind of halteres?). That’s certainly a bizarre life cycle for a strange looking creature; for some reason, I thought bot flies were mostly tropical.
Thanks again, and keep up the good work with the site! 🙂
Best wishes,

Jeff Boetner replies
Hi Daniel and Rhian,
Great shots. Yes, a Cuterebra botfly, this is one of the Cuterebra fontinella bots. You have two subspecies of this bot in WI, Cuterebra fontinella fontinella, which uses white footed mice as a host, and Cuterebra fontinella grisea, which uses deer mice as a host. The one you photographed is very freshly emerged, the wierd face is from a balloon like structure that inflates to help push the fly out of the pupal case, and then it gets reabsorbed back into the face. These guys don’t feed as adults so have no real mouth parts.
It is hard for me to do this one to species, but if you hung onto it, it might get better coloring after it has been alive for a few days. So if you can keep it alive, (they don’t feed so easy to keep), post another picture once the brown turns to white and black. I don’t see these this fresh, very often, unless I have reared one. Very fun to see.
I am doing dna work on bots, and I would be interested in the specimen. I don’t have dna from WI specimens, and still missing grisea if it turns out to be that one? Yours is female for sure from the spacing between the eyes.
Thanks for posting. And thanks for the forward Daniel. Love you site!
Jeff Boettner
Plant, Soil and Insect Sciences

Large fly(?) in Texas
Location: Dallas, TX
October 23, 2011 10:56 pm
Hello WTB
Please help me identify this LARGE fly(?) that my son found in our back yard.
– We live in North Dallas, TX
– It was found today, October 23
– It was found on a piece of playground equipment less than a foot from the ground
– It does not seem able to fly, but buzzes loudly when it attempts to
Thank you for all of your efforts. your site is my first stop when attempting to ID something new that we’ve found.
Signature: Brandon

Rabbit Bot Fly

Hi Brandon,
This is a Bot Fly in the genus
Cuterebra, and we are nearly certain it is the Rabbit Bot Fly, Cuterebra lepusculi, a species we just posted last week.  We are going to copy Jeff Boettner on our response so he can verify the identification since he has been providing correct species identifications for our Bot Fly submissions.  If you still have this specimen, Jeff may request it for study purposes.  Bot Flies in the genus Cuterebra are endoparasites of rodents and they have very interesting life cycles.  Your photographs are excellent.

Rabbit Bot Fly

Daniel –
Thank you for the quick response, and thank you for the compliment on the photos.  I’ve attached a much better photo here, now that I’ve had time to properly set up and shoot this one.
Jeff –
I just read your comments on WTB.  I appreciate all of the great info.  I will indeed post this on  I’m excited about your interest in this find.  This is a first for me, and I do a fair amount of amateur insect hunting and photography.
I do still have the live specimen, and would be happy to share it.  No eggs yet, but I will send those as well if they come.  How should I go about getting it to you in the best possible condition?
Feel free to look through the photos of my other finds on my website. The “nature” section can be found here:
Kind regards,

Rabbit Bot Fly

Hi again Brandon,
Thanks for taking the time to take this stunning new photograph that is artful as well as accurately depicting the morphology of the Rabbit Bot Fly.