What Are Bot Flies? What You Should Know for Your Safety

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are bot flies dangerous

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.

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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 ↩

 

 

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Rodent Bot Fly



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    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.

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  • 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.

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14 Comments. Leave new

  • equalrights4parasites
    January 23, 2011 12:43 pm

    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
  • equalrights4parasites
    October 18, 2011 2:37 pm

    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
  • equalrights4parasites
    October 24, 2011 10:03 pm

    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
  • 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
  • Could these large lumps on a black tailed jackrabbit be from the bot fly mentioned above?
    http://www.pbase.com/arlon/image/163924106

    Reply
  • 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
    • Jeff Boettner
      August 24, 2016 2:45 pm

      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
  • poor deer. whyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyy Rest in peace little deer

    Reply
  • 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

    Reply
  • 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 🙂

    Reply
  • 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!!

    Reply
  • 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!

    Reply

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