Currently viewing the category: "Bot Flies"
What's That Bug? does not endorse extermination

Subject: Bot Fly Larva
Location: North Bay, Ontario, Canada
August 21, 2014 10:25 pm
Hi there,
I am located in North Bay, Ontario, Canada. I have recently found a mouse inside my house walking around pretty slowly. I put gloves on and picked him up to put him outside and when I looked at him I saw a weird brown thing protruding from his side. Upon closer examination I determined it was alive and I recognized it as a bot fly larva that I had read about online a while ago while researching animal parasites. I pulled it out carefully with tweezers, plus about 5 other ones. They were quite large. I have a video of this extraction. I estimate the larger ones were roughly 3cm, maybe slightly larger. Definitely matched the description of rodent bot fly larva. I kept the mouse in a container and fed him until his wounds healed and let him go.
A couple days later (before I let the other mouse go) I was cleaning out and removing a big work tent that was in our backyard that had been used for our house renovations. It was damp, lots of wood scraps etc. I emptied a basket of garbage wood and a mouse emerged from the stuff I was dumping. He was slow and you could actually see two huge bot flies hanging out of him. Very disturbing.
Due to the fact that I have worked extensively in that gross work tent, plus the other mouse was found in our house full of the parasites, some serious questions have come up.
Firstly, how concerned should I be regarding bot fly infections on/in me or my two cats? Is there something I should be looking for on the three of us (obviously a gross black worm thing, but I would prefer to catch it waaaay before that).
Secondly, is this normal??? Are bot flies common this far north? Should I be reporting this, and if so, then to who?
Lastly, how do I avoid coming into contact with the eggs? Are there common types of material they are laid on or environments I could perhaps minimize in order to dissuade them from being laid near my house?
Thank you for your help with this.
Signature: Kate Griese

Bot Fly Larva

Bot Fly Larva

Dear Kate,
Thank you for your thorough and engaging request.  You are correct that this is the larva of a Rodent Bot Fly.  A link from that posting is no longer valid, however we did quote from what might have been the College of Veterinary Medicine at Michigan State University which stated:  “
Cuterebra is a normal bot fly of rodents and rabbits, but can also infect cats, dogs, and man. ”  This online library seems to support that cats can become hosts to Rodent Bot Fly larvae.  Companion Animal Parasite Council indicates:  “Cats and dogs are accidental hosts.”  VCA Animal Hospitals indicates:  “Cats are accidental hosts of Cuterebra larvae. They are most commonly infected when they are hunting rodents or rabbits and encounter the botfly larvae near the entryway to a rodent’s burrow. Most cases of warbles in cats occur around the head and neck.”  BugGuide data on sightings indicates that you are in the normal range for Rodent Bot Flies.  We believe it is highly unlikely that a human will be parasitized by a Rodent Bot Fly.  We will attempt additional research on this when time permits.

What's That Bug? does not endorse extermination

Subject: What bug is this?
Location: Maple Grove, MN
July 26, 2014 4:57 pm
Found in our flower garden today. What is this bug?
Signature: William Huybrecht

Bot Fly

Bot Fly

Hi William,
This is a Rodent Bot Fly in the genus
Cuterebra, and they do not feed as adults.  The larvae are subcutaneous parasites on rodents and rabbits.

What's That Bug? does not endorse extermination

Subject: Black bug
Location: Gunnison, Colorado
July 21, 2014 5:08 pm
I found this bug in my home. I thought it was a bee at first but then with a closer look it seemed to be an oversized fly. I looked up horseflies but the bug I found had widest eyes. What is it?
Signature: Audrey

Bot Fly

Bot Fly

Dear Audrey,
There is enough detail in your images for us to determine that this is a Bot Fly in the genus
Cuterebra, the Rodent Bot Flies, but we haven’t the necessary skills, and we suspect there is not enough image detail for even an expert to determine a species identification.  You can compare your image to this individual from BugGuide that also is identified only to the genus level.  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.”

What's That Bug? does not endorse extermination

Subject: A botfly in the far North?
Location: Far North, Ont., Can.
September 15, 2013 9:23 am
I caught a mouse one night and found that there were four huge bumps on its back. I looked closer and saw what appeared to be botfly larvae in holes on each bump. I froze it and gave it to our local science teacher who dissected it with her class. Here’s a picture of what they dissected. Sure looks like a botfly to me!
I live in Fort Albany First Nation, Ontario, Canada, and I am surprised that there are botflys this far North! But is it really a botfly?
Signature: FAFN Resident

Rodent Bot Fly Larva removed from Dissected Mouse

Rodent Bot Fly Larva removed from Dissected Mouse

Dear FAFN Resident,
We concur that this is a Rodent Bot Fly Larva.  According to BugGuide Data, Bot Flies are found in Canada.

What's That Bug? does not endorse extermination

Subject: Two Larva Eat and Kill Mouse
Location: Mass USA
September 3, 2013 5:08 pm
I caught a mouse in my kitchen. I come to find I was able to because it was injured. I put it into a clear cage to show the kids. I come to find the mouse has a hole in its stomach and Two protruding round items imbedded inside. Which I thought were ticks. The mouse is almost dead anyways. So I decide to keep it in the container and wait to see what happens. I check the next day after work and find the bugs detached from the mouse. Each about a half inch long wiggling around. Not really moving in any direction but just wiggling. I also showed this to a friend who’s an exterminator and he says he’s never seen anything like it, also the mouse may be a rat. If that helps. I’ve always been into bugs and snakes, etc. I have never seen anything like this before. Should I be worried seeing as I caught the mouse in the house?
Signature: Matt

Bot Fly Larva emerges from Mouse

Bot Fly Larva emerges from Mouse

Dear Matt,
Bot Fly or Warble Fly Larvae in the family Oestridae are common endoparasites in mammals, especially rodents.  The adult Bot Fly resembles a bumble bee.  From what we have read, the larvae do not kill the host, so perhaps your mouse died of other causes, or perhaps in the case of small animals, the Bot Fly Larvae can do significant damage.  We will copy Bot Fly specialist Jeff Boettner to see if he can add any information.

Bot Fly Larvae

Bot Fly Larvae

What's That Bug? does not endorse extermination

Subject: Bot fly larva found in house!
Location: Cherokee County, NC
July 24, 2013 7:28 am
We found this fat little fellow slowly inching across the floor of our family room earlier this morning. Last night our cat decided to entertain herself by bringing in a dead mouse, so I think the little maggot likely came from the unfortunate rodent. It measured about an inch when scrunched up in the shape pictured, and a little longer when tying to move.
The mouse appeared to be a common house mouse, so I’m thinking it might be a Rodent bot fly, perhaps?
Signature: Jacob

Bot Fly Larva

Bot Fly Larva

Dear Jacob,
Your Bot Fly Larva photo is a welcome addition to our site.
  Your speculation that it came from the mouse your cat brought in is most likely correct.

What's That Bug? does not endorse extermination