Are Bot Flies Dangerous? Debunking Myths & Revealing Facts

Bot flies are a unique type of fly species known for their parasitic behavior.

These insects have a bee-like appearance, with their larvae being short, pudgy grubs that live as parasites within their animal hosts’ tissues.

The danger posed by bot flies depends on the interaction between the fly and its host.

Human botfly infections, which are caused by Dermatobia hominis, can be painful and may require medical attention.

Conversely, bot flies that parasitize animals, such as Gasterophilus intestinalis, Gasterophilus nasalis, and Gasterophilus haemorrhoidalis, may cause temporary discomfort to their hosts but do not typically pose a life-threatening danger.

Infestations by bot flies are known as myiasis, which is an infection caused by their larval stage.

Certain bot flies target humans, while others may cause myiasis in livestock or wildlife. In some cases, proper precautions and treatments can be taken to minimize potential risks.

What Are Bot Flies?

Bot flies are a type of insect belonging to the family Oestridae, with the most common species being Cuterebra fontinella.

Adult bot flies have several distinct features:

  • Size: They are 15 to 17mm long (roughly 5/8 inch)
  • Color: Black with pale yellow markings
  • Wings: Smoky colored
  • Eyes: Large and prominent

Bot flies are known for their parasitic larvae, which live in the tissues of animals.

Despite their menacing appearance, adult bot flies are generally harmless to humans and animals, as they don’t feed or take in nutrients.

However, their larvae can be a cause for concern.

Larvae of bot flies exhibit different behaviors and development stages compared to other obligatory myiasis-causing flies. These include:

  • Highly host-specific
  • Parasitic nature
  • Limited host range

In terms of comparing different botfly species, some key characteristics include:

  • Size of the adult fly
  • Coloration and markings
  • Geographical distribution
  • Host specificity
  • Larval development stages
  • Level of parasitic behavior

Bot flies may appear to be dangerous due to their size and appearance. However, it is their larval stage that can cause problems for animals and humans.

Life Cycle and Hosts of Bot Flies

Larval Stage

Bot flies begin their life cycle as eggs, which are laid by adult females on a host animal’s fur or nearby vegetation.

For example, the horse bot fly, Gasterophilus intestinalis, can lay between 150 and 1000 eggs on a horse’s body.

Once the eggs hatch, the larvae penetrate the host’s skin, causing myiasis, which is a parasitic infestation.

Some botfly species, like Cuterebra fontinella, primarily target rabbits, while others, like Dermatobia hominis, can affect humans as well.

During this stage, the larvae feed on the host’s tissue and grow larger.

Some species, such as Cuterebra emasculator, are known to specialize in specific host animals, like rabbits or rodents.

Pupal Stage

The larval stage ends when the fully grown larvae leave their host to pupate.

This process involves the larvae burrowing into soil or other suitable material to form a protective casing called a puparium.

Inside the puparium, the bot fly larva undergoes metamorphosis, transitioning from a larval to an adult form.

The pupal stage can last for several weeks or even months, depending on the botfly species and environmental factors.

Adult Stage

Once metamorphosis is complete, botfly adults emerge from their puparium.

These bee-like flies have rudimentary or non-functioning mouthparts, as they do not feed or take in nutrients. Their main goal in the adult stage is to reproduce.

Adult bot flies, such as Cuterebra fontinella, are large, robust flies with a body length of 15 to 17mm. They are typically black with pale yellow markings and smoky wings.

Breeding is the primary focus for adult bot flies, as they do not have a long lifespan. Once they successfully mate and lay eggs on a new host, the life cycle starts anew.

Key Characteristics of Bot Flies:

  • Parasitic
  • Affects various host mammals
  • Causes myiasis in host animals
  • Distinct life cycle stages: egg, larva, pupa, and adult
  • Species-specific host preferences

Pros and Cons of Bot Flies (from Carnivore Perspective):

Pros:

  • Effective as a biological control agent against pest mammals in some environments

Cons:

  • Detrimental to native wildlife populations if not controlled
  • Can affect humans, causing discomfort and risk of secondary infections
  • Difficult to eradicate due to their life cycle and host range

Bot Fly Infestation in Humans and Animals

Infestation in Humans

Bot flies are insects known to cause myiasis, an infection where their larvae (maggots) infest human tissue1. Dermatobia hominis, also known as the human bot fly, is a common culprit of these infestations2.

When a person becomes infected, the botfly larva burrows into their skin, leading to symptoms like swelling, inflammation, and irritation3.

Some potential complications of human infestations include:

  • Infections: Bacteria introduced during infestation can cause infections4.
  • Skin lesions: The burrowing larvae can cause painful ulcers or lesions5.
  • Severe health problems: In some cases, the infestation can result in fever, chills, nausea, vomiting, and headaches6.

To treat a botfly infestation in humans, medical attention is crucial.

A physician will typically diagnose the issue and recommend surgical removal of the larvae, followed by antibiotics to reduce infection risks7.

Infestation in Animals

Apart from humans, bot flies such as Cuterebra fontinella also infest animals, particularly mammals like dogs and other pets8.

The infestation process is similar to that in humans, with botfly larvae burrowing into the animal’s skin, causing irritation and swelling9. Sometimes, these infestations can lead to noticeable warbles or lumps10.

In animals, bot fly infestations are typically addressed by veterinarians using methods like:

  • Surgical removal: The botfly larvae are removed from the animal’s skin11.
  • Antibiotic ointment: To reduce infection risks, vets apply appropriate medication12.

Possible complications and risks for animals include:

  • Infections: Similar to humans, animals can develop bacterial infections from infestations13.
  • Odor: Infestations can cause an unpleasant smell as the larvae pupate14.
  • Inflammation: The burrowing larvae might lead to inflammation and irritation on the animal’s skin15.

Recognition and treatment for bot fly infestations in animals are essential to prevent complications or further health issues.

Geographic Distribution of Bot Flies

Bot flies are primarily found in the Neotropical regions, ranging from Southern Canada to Northeastern Mexico and throughout South America1.

They frequently inhabit tropical areas, making their presence notable in countries like Mexico2. In the United States, their distribution extends across the continental US, excluding Alaska2.

One common species, Cuterebra fontinella, can be found in most of the continental US, Southern Canada, and Northeastern Mexico2.

Adult bot flies, like Dermatobia hominis, are known to capture female mosquitoes and lay their eggs on them1.

Features of Bot Flies:

  • Large, robust flies with rounded heads3
  • Chunky, beelike appearance3
  • Adult bot flies are not commonly seen3

Characteristics of Bot Fly Larvae:

  • Short, pudgy, and segmented3
  • Live as parasites in the tissues of animals3
  • May form a bulge (warble) under the skin of the host3

While bot flies can cause discomfort to their hosts, they are not typically considered dangerous to humans4. However, it’s still essential to remain cautious in areas where they are commonly found.

Prevention and Treatment of Bot Fly Infestations

To prevent bot fly infestations, consider the following measures:

  • Avoid high-risk areas: Bot flies are common in the continental US, southern Canada, and northeastern Mexico. So, remain cautious when you travel through these regions. Depending on their type, bot flies can infect mammals, pets, or livestock.
  • Use insect repellent: Apply repellent to skin and clothing to ward off mosquitoes, ticks, and fleas that can transmit bot fly larvae.
  • Cover up: Wear long sleeves, pants, and closed shoes to minimize skin exposure in areas where bot flies are prevalent.
  • Inspect pets: Check your pets for any suspicious lumps or bumps that could indicate the presence of bot fly larvae.

Treatment Methods

The following methods can help treat bot fly infestations:

  • Seek professional help: Consult a physician or veterinarian for proper diagnosis and treatment.
  • Surgical removal: In some cases, surgical removal of the larvae might be necessary. A doctor or veterinarian can take appropriate measures to remove the parasite safely.

Pros

  • Effective in removing the parasite
  • Prevents secondary infections

Cons

  • Requires medical attention
  • Can be painful, depending on the location of the larvae

Home removal: In some instances, home remedies can help remove bot fly larvae. For example, placing a piece of tape over the breathing hole can prompt the larva to come out.

However, this method should be used with caution and only after consulting a healthcare professional.

Pros

  • Cost-effective
  • Can be done without medical assistance

Cons

  • May not be successful in all cases
  • Can cause discomfort or harm if not executed correctly

Antibiotic ointment: After the larva is removed, applying antibiotic ointment can prevent infections and promote wound healing.

Therefore, adopting preventative measures and seeking timely treatment can help minimize the chances of a botfly infestation becoming a serious problem.

Conclusion

Bot flies can be considered dangerous to certain animals due to their parasitic nature and potential to cause myiasis.

While they typically do not pose a direct threat to humans, human botfly infections can be painful and require medical attention.

Understanding the life cycle and behaviors of bot flies can help debunk myths and reveal the facts about their potential risks and appropriate prevention and treatment measures.

Footnotes

  1. CDC – Myiasis – Centers for Disease Control and Prevention 2 3
  2. CDC – DPDx – Myiasis 2 3 4
  3. CDC – Myiasis – Centers for Disease Control and Prevention 2 3 4 5 6 7
  4. CDC – Myiasis – Centers for Disease Control and Prevention 2
  5. CDC – Myiasis – Centers for Disease Control and Prevention
  6. CDC – Myiasis – Centers for Disease Control and Prevention
  7. CDC – Myiasis – Centers for Disease Control and Prevention
  8. Bot Flies [fact sheet] | Extension
  9. Bot Flies | Livestock Veterinary Entomology – Texas A&M University
  10. Bot Flies [fact sheet] | Extension
  11. Bot Flies | Livestock Veterinary Entomology – Texas A&M University
  12. Bot Flies | Livestock Veterinary Entomology – Texas A&M University
  13. Bot Flies | Livestock Veterinary Entomology – Texas A&M University
  14. Bot Flies [fact sheet] | Extension
  15. Bot Flies | Livestock Veterinary Entomology – Texas A&M University

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 – Rodent Bot Fly

Subject:  Rodent Botfly?
Geographic location of the bug:  Portland, OREGON
Date: 08/06/2018
Time: 06:52 PM EDT
Your letter to the bugman:  I found this very large fly-like creature in my garden yesterday. After much research I came across photos on your site that led me to my tentative i.d. We have a growing rodent population in our yard since the last of the outdoor cats disappeared . I was stomping burrows closed when I found this thing and wonder if it might be a female that was laying eggs.I read that they lay eggs in/near the mouth of a burrow that hatch instantly to attach to a passing rodent. I wonder if these things (eggs) can attach to shoes or garden gloves and get tracked in the house. Creeeeeepy!!
How you want your letter signed:  Bjam, Portland, OR

Rodent Bot Fly

Dear Bjam,
You are correct that this is a Rodent Bot Fly and of all the species pictured on BugGuide, it appears most like
Cuterebra tenebrosa based on this BugGuide image.  According to a comment from Jeff Boettner on this BugGuide posting:  “The bot uses Neotoma (wood rats) as a host. They can get in the wrong hosts, if you had cuts on your hand or touched your eye. It would be pretty hard to get this bot in you, and would not be able to complete development in you at any rate. So easy to get removed if you found it trying to use you as a host.”  With many species of Flies, the sexes can be distinguished because the eyes of the male are much closer together than the eyes of the female, and we believe your individual is most likely a female.  According to BugGuide:  “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.”  If temperature was the only factor in the hatching of the eggs, heatwaves would cause eggs to hatch with no nearby host, so in our opinion, the hatching of the eggs might be more complicated.  If eggs were tracked into the house, and there was no host present, the larvae would die.  We will contact Jeff Boettner to see if he can verify the identity of your Rodent Bot Fly and to see if he can provide any additional information.

Rodent Bot Fly

Thanks for the quick reply.
I used to work for a veterinarian and we occasionally saw cuterebra larvae in dogs. Impressive.  Have also seen deer mice that carried 3 or 4 or more larvae. They were almost more maggot than mouse.
We don’t have woodrats here so I suspect deer mice, voles, possibly chipmunks and rats are main hosts.
Thanks again for response.  Love this site.  It’s a great resource!

Jeff Boettner responds with correction.
Daniel–Not a bother at all. Love these. But I am not sure what you have yet!  For sure NOT C. tenebrosa (which lacks the spotting of yours on the abdomen) but it is female.
Looks like a Peromyscus bot of some sort. It looks from the picture,  like the person might have collected it? We created a team of people to do dna sequencing to work out some of these tricky ones, if the person is willing to part with it? I am ccing Socrates on this (he is starting up a PhD project this fall on bot evolution and can really use samples of even common bots that show up). This would be a really nice one to see in hand.
Nice pics!  I should be able to figure out a name but I want to think about this one more. These mostly black females are tricky. But I am quite sure this is not C. tenebrosa
Socrates: See pics at this site:  2018/08/07/rodent-bot-fly-12/
Will get back to you soon.
Jeff Boettner

Additional information from Jeff Boettner
I think your bot is Cuterebra approximata female. Will see if he thinks so too. Generally these females are all black but the range fits and the males have spotting on the abdomen similar to yours. These mostly black females are very tricky. But this one uses Peromyscus maniculatus as a host, and is found in OR.  Would be a really nice one to preserve.
Jeff

Thanks for this info. Unfortunately, I released it after a couple of days. I have the glass it was in with a good smear of fly poop if that would be of any use. Also more photos.
Bjam

Letter 2 – Nasal Bot Fly Maggots in Deer

worm
December 12, 2009
A friend was cleaning a recently harvested florida whitetail deer and inside the jaws of the deer they found some kind of worms that were about the size of the first 2 joints of a females pinky finger. They were white and had pincher like things on what I’m assuming is the head end of the worm.
Susy
Central Florida

Nasal Bot Fly Maggots in a Deer
Nasal Bot Fly Maggots in a Deer

Hi Susy,
We are quite excited to get your image of Nasal Bot Fly Maggots in a Deer’s head.  According to the Missouri Department of Conservation Website:  “Nasal bot flies (Cephenemyia spp.) are common parasites that infest the nasal passages of deer. They most often are found by taxidermists while preparing heads for mounting, although hunters occasionally notice them.  Adult female flies deposit small larvae in the nostrils of the deer. The larvae enter the nasal passages and pass through several stages of development and growth. They are liberated when the deer sneezes. They then form a pupa and emerge as an adult fly.  Although quite large (up to 1 1/2 inches) and unpleasant looking in the final stages of development, nasal bots cause little harm to the deer and do not infect humans. They also do not affect meat quality.
”  According to BugGuide:  “Eggs hatch inside the female fly and the newly emerged larvae are deposited in the nostrils of a suitable host. These larvae quickly migrate through the nasal passages into the nasopharyngeal (throat) region, preferably in the throat (retropharyngeal) pouches (causing nasopharyngeal myiasis in the host), where they settle and develop. After development is complete, the mature larvae are expelled from the host and pupate in the soil. Adults emerge after 2-3 weeks; since they do not feed, their life span is short and mating quickly ensues to complete the life cycle. 2 generations have been reported from the north, with the duration of each life cycle varying with the season. The winter life cycle can take up to 6 months, while the summer life cycle, half of that time.  Remarks  Usually the larvae do not cause considerable harm to the host other than mild irritation. However in the case of heavy infestations, results can be fatal for the host (death by suffocation), and consequently for the larvae (which, since are true parasites, cannot survive without a living host). Some members of the genus (e.g. C. trompe) are pests in reindeer farms in Europe, causing significant mortality and economic loss.”

Letter 3 – Rodent Bot Fly

HUGE FLY
Please help me Bugman. .
I caught this fly, however, this is the biggest fly I have ever seen!! Its over an inch long and its so fat it cant fly, maybe ready to give birth to a small child or something? I thought it was a bee of some kind at first but it resembles more of a fly than anything. The pictures make it look small but this thing has some serious girth to it. Let me know what I have please. I’m really boggled and amused!! Thanks,
R.E

Hi R.E.,
This is some species of Bot Fly in the family Oestridae. They are also called Warble Flies. They are host specific. Some are parasitic on rodents like squirrels and rabbits, and there is a human Bot Fly in the tropics. The maggots burrow into the skin and cause a large bump with an open sore known as a warble. Not a pretty picture. Sorry we can’t identify the species. Perhaps Eric Eaton can. Here is what Eric wrote: “The bot fly is a rodent or rabbit bot in the genus Cuterebra. The adults do not feed. In fact, tey have no mouthparts! They live briefly, fueled by fat stored in the larval stage. Male bots practice ‘hilltopping,’ whereby they stake out a perch on a promontory, the better to intercept females flying below. These are not commonly-encountered flies, despite their relative abundance.”
.

Letter 4 – Rabbit Bot Fly

Black and White Bumblebee-Like Relative Found near Yosemite? Sat, Apr 11, 2009 at 3:12 PM
This might be some sort of mutant insect, because it certainly beats me. I found it rolling amongst the pebbles outside my mountain home near Yosemite, where many common bumblebees and honeybees flourish. Something is definitely off… Instead of mouth parts it has nostril like holes and the flesh above the undersized wings (it cannot fly) appears withdrawn, or peeled up.It’s first two segments have a white furry underbody and a shiny hard top. It’s last segment is shiny and hard. It has no antennae. It’s eyes are black with two red spots, one on the top and the other on the bottom portion. I figure mutations might not be your forte, but is this just a really weird insect? He’s also about an inch long.
Interested Mountain Girl
Coarsegold, near Yosemite Valley, CA

Rodent Bot Fly
Rabbit Bot Fly

Dear Interested Mountain Girl,
We wonder how long you are going to maintain your interest when you learn that though it looks like a Bumble Bee, this is actually a fly, a Bot Fly to be exact. We believe it is a Rodent Bot Fly. Bot Flies are endoparasites of various mammals and they cause swellings knows as warbles, giving the Bot Fly the name Warble Fly as well. Rodent Bot Flies tend to parasitize squirrels and rabbits. In Central America, there is a Human Bot Fly.

Wow, this is actually even cooler. I hadn’t realized we had those here, but I’d not paid much attention to the insect and bug life since I moved here a few years ago. Sorry for the poor picture quality, the camera wasn’t working at it’s best, but thank you for the amazing and prompt response, you guys really are amazing bug people!
Right now my little Bot buddy is in a glass jar with a damp paper towel and a few leaves, and he seems to be getting more active by the hour! I’ll free him pretty soon, and he can go back to his biting, buzzing ways, much to the chagrin of the local voles and bunnies.
-Interested Mountain Girl

Letter 5 – Rodent Bot Fly

Black & white bee?
Location: Washington wetland field
July 19, 2011 10:58 am
Help me find out what this is. It was seen in a wetland field here in the state of Washington. It’s the same size as a bumble bee. I didn’t see it fly, it does appear to have wings. It is also fuzzy like a bumble bee. Thanks
Signature: P Lind

Rodent Bot Fly

Dear P Lind,
You have encountered a Rodent Bot Fly in the genus
Cuterebra.  According to BugGuide:  “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.”

Letter 6 – Rabbit Bot Fly

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 BugGuide.net.  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:
http://www.themcmurrays.net/photos/nature/index.html
Kind regards,
-Brandon

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.

Letter 7 – Rodent Bot Fly

Subject: Bee
Location: Orlando Florida
November 4, 2016 7:07 pm
Ok, so I found this bee by the pool, and I’m extremely curious as too it’s species! I believe it’s of the Apidae family, and its stingless. I have a pretty good picture, I really hope you can tell me what species it is!
Signature: Thank you! Maihaa

Rodent Bot Fly
Rodent Bot Fly

Dear Maihaa,
Though it resembles a Bumble Bee, this is actually a Rodent Bot Fly in the genus
Cuterebra.

Thank you! That’s fascinating! I’ve decided to do more research on it, for some reason I find it quite intriguing. Is there anything more you can tell me about it?
Maihaa

Hi again Maihaa,
The larvae are endoparasites on rodents that do not harm the host, which is hard to believe.  See our Bot Fly archives and BugGuide for additional information.

Letter 8 – Rodent Bot Fly

Subject: Unidentifiable bee?
Location: Southeast Michigan
April 28, 2017 10:30 am
Dear bugman,
I found this bug in my bedroom this morning. Cool looking! What is it?!
Signature: Julie Jones

Rodent Bot Fly

Dear Julie,
Though it is frequently mistaken for a Bee, this is actually a Rodent Bot Fly in the genus
Cuterebra.

Letter 9 – Rabbit Bot Fly

Subject:  Fly?
Geographic location of the bug:  Greely Colorado
Date: 08/04/2018
Time: 02:56 PM EDT
Your letter to the bugman:  This little guy was found in a back yard. The fingers are those of a toddler who would like to know what this is. I can’t find it by googling.  Thank you for any help!
How you want your letter signed:  Mallory

Rabbit Bot Fly

Dear Mallory,
Most people who encounter a Bot Fly in the genus
Cuterebra for the first time confuse it for a Bee.  According to BugGuide:  “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.”  BugGuide also notes:  “Habitat is less important to these flies than the host mammals. Habitat-specific rodents or rabbits means habitat-specific species of bots.”  We believe your individual is a Rabbit Bot Fly, Cuterebra buccata, which is pictured on BugGuide.  We have written to Bot Fly expert Jeff Boettner to confirm its identity.  Do you have any additional camera angles?

Rabbit Bot Fly

Jeff Boettner responds.
 Both C. leupusculi and C. buccata are possible in Greely, CO. Both these species look a lot alike from the side, but the coloration of the back hints more of C. leupusculi. I think this is a male but also hard to tell from this angle and there are only 15 C. leupusculi males in collections, females are more often seen. Males may lek, ie if you went back to this same spot at the same time of day, you might see males fighting over that rock or the nearby area? Do you have any other pics from any other angles? Even slightly different angles.
C. buccata uses S. floridanus,  whereas C. lepusculi uses S. audubonii but both rabbits overlap in that location. So a bit tough to call. But for sure a rabbit bot, and likely one of these two.
Jeff

Letter 10 – Rabbit Bot Fly

Subject:  Botfly
Geographic location of the bug:  Byron center MI
Date: 07/19/2020
Time: 11:10 AM EDT
Your letter to the bugman:  I believe this is a type of botfly?
How you want your letter signed:  Evan

Rabbit Bot Fly

Hi Evan,
You are correct that this is a Bot Fly, and thanks to this image, we believe it is
Cuterebra abdominalis which is pictured on BugGuide.  According to BugGuide, the host is cottontail rabbits.  Your images are awesome.

Rabbit Bot Fly

Authors

  • Daniel Marlos

    Bugman aka Daniel Marlos has been identifying bugs since 1999. whatsthatbug.com is his passion project and it has helped millions of readers identify the bug that has been bugging them for over two decades. You can reach out to him through our Contact Page.

  • Piyushi Dhir

    Piyushi is a nature lover, blogger and traveler at heart. She lives in beautiful Canada with her family. Piyushi is an animal lover and loves to write about all creatures.

14 thoughts on “Are Bot Flies Dangerous? Debunking Myths & Revealing Facts”

  1. Mountain Girl,
    Wow! Did you take any other pics of this fly before you released it? This is for sure a rabbit botfly of the Genus Cuterebra. The undersized wings are actually halteres, which help stabilize the flies in flight, (these guys are very fast fliers). They are reluctant to fly, because bots have no mouthparts (and cannot feed or store new energy) and therefore are born with fat reserves that are depleted with each flight. They generally live only 10 days or so.
    It is too bad this picture is so blurry. I believe this may be a photo of Cuterebra cochisei, which is only known from 1 male and 1 female specimen! If so this would be only the third record of this species. But it would help to see this fly from other angles. If you have any other pics, even blurry ones, please post them. The only 2 other specimens were collected in AZ in fall, so I am hesitant to call yours this species for sure. But it is not a common bot. This one has me confused, but it is a rabbit bot for sure from the red spots in the eyes. Thanks for the post! Great find. Yours may be the only picture of this species alive with the eye spots. The eye spots disappear after death.

    Jeff Boettner

    Reply
  2. This is Cuterebra fontinella, a mouse bot. Can’t tell much more from the photo. This is a common bot throughout the US. It uses Peromyscus as the host.
    Jeff Boettner
    Plant, Soil and Insect Sciences
    UMASS-Amherst
    Amherst, MA
    boettner@psis.umass.edu

    Reply
  3. Hi Brandon,
    Awesome! It is indeed the female, to the male fly seen last week in TX as well and posted at this site. Its a female Cuterebra lepusculi. Easy to ID with the red spots in the eye (typical of rabbit bots) and the classic white U shaped pattern when viewed from above. Neat to see the male and female in the same week. Would love to have you post to BugGuide.net if you are up for it. We don’t have the female pictured yet at that site.

    This is a parasite of cottontail rabbits in your area. This species uses cottontail rabbits Sylvilagus nuttallii over most of its range and S. audubonii, the desert cottontail in the rest of the range. See the other post from last week to see the range.

    Email me (address below: as I would like to know more about it. If you collected it I would love to get it for a dna study we are doing. I actually just got back from a meeting with a world expert on flies that is going to help us to look at the genetics of bots. So amazing timing.

    The red eyes will turn black when the bot dies. These bots do not feed as adults (they have no mouthparts). So they only live for about a week to 10 days. It is best to keep bots alive as long as you can if you are keeping it. If bots are killed too quickly and pinned, they will turn black and oily looking and may just rot– they are pure fat as adults. So best to let them burn off fat in a cage or container. Yours is female and she may start laying eggs in captivity. In case she has mated, don’t let kids handle the eggs. If you touch the eggs and then touch an open wound or your eye, the eggs could hatch and try to get into you. Unlikely they would hatch, but it does happen with some female bots. I would be interested in seeing the eggs as well if she does.

    Email me direct and I can answer any questions you might have.

    Really fun find. Thanks a bunch to the staff at What’s that bug! for contacting me about this one. Do let me know about any bots you come across.

    Jeff Boettner
    Plant, Soil and Insect Sciences
    115 Ag. Eng. Bld.
    250 Natural Resources Road
    UMASS-Amherst
    Amherst, MA 01003

    boettner@psis.umass.edu

    Reply
  4. Found this site on a google search after looking for info on these (found in a deer today)
    Was going to add some photos I took, but am not sure how to do that here

    Reply
    • Dear Cottonwoodz,
      You should use our standard submission form that requires some information about location and then you may ask a question if you have one, or just provide any additional commentary on the sighting that was interesting and unusual, and then you may attach up to three photos.
      Here is the link to our standard submission form:
      http://www.whatsthatbug.com/ask-whats-that-bug/

      Reply
  5. Curious about the size of the bumps you mention the bots show up on rabbits as “large” lumps – is that the size of a pea?
    When my puppy first came to me , he had a lump on his side – noticed it was getting bigger and when it was about the size of a pea, I took him to the vet. The vet was very excited with the “find” of a fly larva – probably a bot?
    Thank you!

    Reply
    • Hi Varietypak,

      They can range from the size of a pea when starting out, to almost 2 inches for the rabbit bots. Not common in dogs and cats but if they eat a mouse with a bot the bot may try and use the new host. Or if they lick a plant with an egg on it. But most bots are very host specific.

      Reply
  6. Currently, I live in rural NW Oregon, about a half hour outside of Astoria, and we have a chipmunk with five botfly larvae under its skin. Recently, a new species of very large squirrel arrived. This is a type we have never seen before. It’s 4-5 times LARGER than any of the other native squirrel species and within days it had chased out all the other squirrels and most of the chipmunks. Turns out, this new squirrel species is from the Yucatan peninsula in Mexico and according to a few websites, it migrated up here because of A) it’s too hot on the Yucatan, and B) the forest fires in CA. I’m wondering if there is some kind of connection and who should we report this botfly infestation to? Is there still someone studying this? We’ve had some very hot days up here and I worry about our other animals and other local wildlife.
    Thank you, Eva in Oregon

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  7. Hello, I found this thread after a search to figure out what kind of bug my kids found in our house. I see that someone was once interested in having the insect in-hand. I still have it in the jar (though nearly dead) and it looks exactly like the one in the photos in this thread (including the spotted, bluish body). Does anyone still want one? You can have mine 🙂

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  8. Hello, I am also in Oregon (central coast range, just inland from Newport). We found a chipmunk with two botfly larvae that emerged from it’s abdomen shortly after it’s death. I’ve never seen anything like this before, it’s the most disgusting thing I’ve ever seen. Brown, large, chewed it’s way out. 🤮 I have pics and video. Hope this isn’t a invasive or common thing, hope my dog doesn’t get it. She’s squirrelin’ all the time… Nightmarish!!

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  9. I have (currently) live botfly larvae that emerged yesterday evening from a recently deceased chipmunk (my dog got ‘er). I’m in the central Oregon coast range (near Siletz, inland from Newport/Lincoln City). The larvae emerged from it’s abdomen, and a second one began to emerge as well. It’s the most disgusting thing I’ve ever seen. Could my dog get these nightmarish parasites!? She’s squirrelin’ all the time, it would be impossible to keep her from their trees and trails, we live in the woods. The larvae is big and brown and about an inch or more. I have pics and video. So gross!

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