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.

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.

2 thoughts on “Rodent Bot Fly”

  1. 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 🙂

  2. 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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