bot fly larvae and a bit of a warning to view photos

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Juile Grahn

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Aug 5, 2021, 4:05:03 PM8/5/21
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I saw something I had never seen before yesterday and I have to admit it was a bit creepy.  If you don`t have a stomach for “creepy" don`t open my next email with the photos.    

A chipmunk was dispatched in our yard yesterday and on its underside were these weird looking dark things.   I took a closer look and you could see that each of these dark things was part of something much larger beneath the skin of the chipmunk.  I went back inside to fetch my phone and when I got back one of the things had come out of the chipmunk and was moving on the sidewalk near it.  I was not expecting that!   To me it looked like an insect larva.  I tried to remove another of these things (with gloved hands) and it was not easy.  It tried pulling itself back in and was rather hard to get it out.  The outside of them was tough, sort of like leather and covered with tiny spines.   They had a definite odor to them too.  I am glad I had breakfast before this little encounter.  I will send photos in a bit and the last photo is of the empty cavities under the skin where these things had been.

I googled "parasites on chipmunks" and one of the first things listed was bot fly.  The photos a chipmunk with bot fly larvae in them on line looked just like my photos.  I was relieved to read that this particular bot fly is not interested in humans.  I knew there were insects called bot flies that parasitize animals but really did not know of their life cycle until I started reading.  Even though it is rather creepy it is quite interesting.

The adult bot flies mate and the female deposits it`s eggs along runways or in tunnels the chipmunks use.  The eggs are stimulated to hatch when they are exposed to the heat given off by the chipmunk.  One article I read said increased CO2 levels can play a role in when they hatch too.  Once hatched they resemble a little maggot.  These then hop aboard the chipmunk and enter their body through openings like the eyes, mouth or a cut on the skin.  They then move through the body to a warm area and start growing beneath the skin in what is called a “ warble”.  They cut a small hole in the skin of the warble for breathing.  They feed on white blood cells until they become the large larvae you see in my photos.  Then they wiggle their way out of the warble on the chipmunk and make their way to the soil where they pupate like a moth does in its cocoon.  After a period of time an adult fly emerges and the cycle starts over.  Some pupa can overwinter before the fly emerges.  Different species of bot flies parasitize different species of mammals, humans included, but those species do not occur around here.  The species that is on this chipmunk can also be found on other small rodents and rabbits.  It is likely of the genus Cuterebra and family Oestridae.  This parasite does not necessarily kill it`s host.  The warbles can heal up after the larvae leave but sometimes they can get infected and end up killing the host.  They can be more fatal when the larvae get on young hosts.  

Anyone knowing more about these bot flies feel free to add to this and if you see I am incorrect please say something.  What I have written comes from a few different sources.  

Julie Grahn
Cook Area

norma malinowski

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Aug 5, 2021, 4:47:02 PM8/5/21
to Juile Grahn, Ely Field Naturalists
I had one in my head after a trip to Belize.  It hurt like heck when it was chewing.  I could hear it chomping.  Dr Bianco had to surgically remove it. 

Norma Malinowski
Stay Safe

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clever...@gmail.com

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Aug 5, 2021, 4:48:40 PM8/5/21
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TMI !!!!

Beckie Prange

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Aug 5, 2021, 4:53:13 PM8/5/21
to Steve Wilson, norma malinowski, Juile Grahn, Ely Field Naturalists
Bot flies have made my skin crawl ever since I first learned about them as a child. Julie, thanks for sharing this with the photos and your research in spite of reactions!

Beckie

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Beckie Prange
Assistant Scientist, Site Manager
UMN Hubachek Wilderness Research Center
425 Shady Lane
PO Box 96
Ely, MN  55731

chip hanson

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Aug 5, 2021, 9:16:55 PM8/5/21
to Beckie Prange, Steve Wilson, norma malinowski, Juile Grahn, Ely Field Naturalists
We generally see 2 to 4 cases a year in pets .   Interestingly almost exclusively in dogs under 10 pounds.   I have always assumed that  the small size fit more with the search image of the fly  looking to do its thing on mostly small rodents, squirrels, rabbits etc.   We consider the removal of a big juicy wriggling bot fly one of our most delightful procedures…..especially if we can do it in front of a completely mortified client !!!   We always feel really good for the pup.  I would suggest that the larvae doesn’t exactly “chew” on the host as much as irritate the host tissues so that the tissue oozes nutritious serous fluid which the larvae laps up.  They do move around a fair bit and I could imagine how it would feel like chewing.  It is not in the bots interest to kill the host….which would result in the bot loosing its food supply and not making it to full development.   I would imagine that it was not the presence of the bot that killed the chipmunk

Michael Joyce

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Aug 6, 2021, 9:18:47 AM8/6/21
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Hi everyone,

Nothing like bot fly pictures and discussion to kick off a Friday! And for clarification, that wasn't meant to be sarcastic. 

For those of you that may be interested, attached is a recent paper on individual and environmental factors that influence bot fly infection prevalence in chipmunks. The study was conducted using a 12-year dataset from eastern Quebec, southeast of Montreal and just north of Vermont. 

They found some interesting effects of weather (positive association between temperature and precipitation on bot fly infection intensity), population size (positive effect with infection intensity), beech mast cycles (negatively associated with infection prevalence, so chippies in good nutritional appear less likely to become infected), and interactions between personality, sex, and age on infection prevalence.  For adults, males that were quicker to explore were more often infected than those that were slower to explore. For juveniles, those emerging in spring were more likely to be infected than those emerging in fall. 

Take care,

Michael Joyce
Wildlife Ecologist
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Natural Resources Research Institute (NRRI)
University of Minnesota Duluth
5013 Miller Trunk Hwy, Duluth, MN 55811
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NRRI Mission: Deliver integrated research solutions that value our resources, environment and economy for a sustainable and resilient future. 
Paquette_2020_bot_fly_parasitism_eastern_chipmunk.pdf

Mike Ruzich

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Aug 7, 2021, 9:59:36 AM8/7/21
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About ten years ago, during April, at the end of a long particularly tough winter a yearling buck approached me, and then actually approached my dog. It was drooling, and just hung around the cabin. We put some alfalfa out for it, but the deer wouldn’t touch it,  so I got in touch with the DNR for possible CWD case. The DNR was right on it, but by the time they reached the deer, it was dead. A field necropsy was done, and the salivary glands were fine, so no CWD. Starvation was the cause of death. But the DNR agent kept digging and pulled out a number of botfly larva. She said they don’t seem to hurt deer. Flys lay their eggs in deer nostrils, eggs hatch and larva crawl into and lodge in deers throat, and drop out in Spring.

Sent from my iPad

On Aug 5, 2021, at 3:47 PM, norma malinowski <bogwa...@gmail.com> wrote:



Juile Grahn

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Aug 8, 2021, 8:56:00 AM8/8/21
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Thanks for adding this.  A few years ago couple different people in the Cook area saw deer with large swellings along the upper part of their necks and rear of the jaw area.  I don`t remember the exact time of year but it was not during the winter.  The deer were alive when seen and never examined.  One person did check with the DNR and was told it was likely an insect causing the problem and that the swellings would eventually go away.  I wonder if that was bot fly related too.  I had forgotten all about that until you brought it up now.

Julie

Michael Joyce

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Aug 8, 2021, 9:46:21 AM8/8/21
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Hi everyone,

Deer botfly (Genus Cephenemyia) is in the same family as rodent botfly (Genus Cuterebra), but they are quite different from rodent bots regarding how they infect their host. Deer bots do not grow within muscle tissue like rodent bots but instead attach to pouches near the back of the tongue. I have seen deer botfly numerous times in deer in Minnesota. From what I understand, you can't typically tell if a deer is infected with nasal bots from external examination. But it sounds like they can cause swelling and inflammation of the retropharyngeal pouches where the bots set up shop, so it may be possible that the large neck swellings on the deer in Cook were caused by bots.  I don't think deer botfly can cause starvation, but it sounds like they can cause suffocation in rare situations of extraordinarily high infections. 


Michael Joyce
Wildlife Ecologist
- -
Natural Resources Research Institute (NRRI)
University of Minnesota Duluth
5013 Miller Trunk Hwy, Duluth, MN 55811
- -
NRRI Mission: Deliver integrated research solutions that value our resources, environment and economy for a sustainable and resilient future. 

Carl Karasti

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Aug 9, 2021, 11:00:11 PM8/9/21
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Since the topic of bot flies seems so popular here (Ha!), I thought I'd share a story about a fly and a cat.  A cat we had a few years back suddenly started acting strangely.  It would go from being perfectly normal to suddenly flopping violently all over the floor, then it would lie there quietly for a while and finally get up and seem quite normal again.  Until the next time that it would suddenly go into the violent spasms of another fit.  I called and talked to Dr. Chip and then brought the cat in for him to check out.  Chip's diagnosis was that a fly that typically lays its egg in the nostril of a rabbit or hare will sometimes instead lay its egg in the nostril of some other critter, such as a cat.  I don't recall if he said it was a bot fly, it may have been some other type of fly - perhaps he will chime in here to offer more.

Warning:  the rest of this story, although interesting, might make some folks a bit squeamish.  You have been warned ....

After the egg hatches, the larva makes its way up the host's nostril and burrows its way through the head and into the host's brain.  Sounds like something out of a horror movie, but it's real.  Over time, the larva randomly burrows its way around in the host's brain, which means it is randomly snipping its way through some of the neural circuits, the wiring of the host's brain, which can seriously disrupt the functioning of the brain.  [I vaguely recall watching, a long time ago, some sci-fi type movie about an earwig burrowing in through an ear and into a man's brain and doing the same thing to him.]  Most of the time, our cat would be just fine between the fits it experienced.  Then it lost most of the use of its back right leg but it seemed otherwise quite well and happy.  I used a piece of leather to fashion a brace to hold the cat's leg in a normal walking position, which allowed it to walk around quite well because its hip muscles still functioned well, the cat had only lost control of the lower leg and foot.  Amazingly, the cat tolerated the light weight, soft and slightly flexible leg brace very well and appreciated being able to get around pretty normally.  There did come a point, though, when the cumulative brain damage finally became too great, or some critical damage was done, and our cat finally died, but it took a while, although I no longer recall how long it was from the first fit we observed until its passing - maybe a couple of months or a little longer.

Coincidentally, Chip had just had another cat he had worked with that had suffered the same ailment  with similar symptoms and after it died its brain had been autopsied and the larva had been found within.  This had primed Chip for a quick and accurate diagnosis of what was ailing our cat.  This certainly was no fictional sci-fi story for our cat, it was very real.  Unfortunately, there is nothing that can be done to save the afflicted animal.  Ever since this experience, many times I've wondered how many rabbits or hares end up suffering a similar fate.

Carl Karasti

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