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Native Californian, biologist, wildlife conservation consultant, retired Smithsonian scientist, father of two daughters, grandfather of 4 small primates. INTJ. Believes nature is infinitely more interesting than shopping malls. Born 100 years too late.

Tuesday, September 23, 2008

Emergence of the bot flies

The grisly subject of botflies revisits me at this time of year, because August and September is when I find them floating in the swimming pool.

My earlier unconfirmed discovery of a bot on a western tree squirrel elicited quite a few comments, including this one by bot fly expert Frank Slansky at the University of Florida. His webpage on the topic is worth a visit.

"Can you clarify-- was that pic of the sq on your website from California? It looked like a western gray squirrel, but I'm not certain.

[CW: Yes, it was a western gray squirrrel.]

"The issue is that there is only one known species of Cuterebra (C. emasculator, the "emasculating" bot fly, which actually doesn't emasculate its hosts!) that normally infests tree squirrels, and it only occurs east of the Mississippi. So there are three possibilities about the squirrel you photographed:

1. There is a western spp of Cuterebra that typically infests sqs which has not yet been 'discovered' and identified by entomologists;

2. The eastern species of Cuterebra that infests squirrels has somehow spread to the west coast, perhaps because some of the eastern gray squirrels that were introduced on the west coast were infested with Cuterebra;

3. The squirrel you photographed was 'accidently' infested by a species of Cuterebra that typically doesn't infest squirrels. Each species of Cuterebra is fairly specialized in its 'typical' hosts-- one species of Cuterebra may typically infest only wild mice, another only wild rats, another only rabbits, etc. But sometiumes an 'odd' host gets infested, such as a raccoon or house mouse-- sometimes even cats, dogs and people, although there are no species of Cuterebra that typically infest these animals. They just 'accidently' get infested when they encounter some bot fly eggs laid in the habitat of the 'typical' hosts.

"I think #3 would be the most likely explanation for that squirrel-- when running on the ground it may have encountered some eggs of a mouse-infesting or rabbit-infesting Cuterebra and became infested that way. Larvae of the mouse-infesting species often settle in the groin area of mice.

"Anyway, it's probably a very rare occurrence, but if you see other western tree squirrels with these bot fly lumps ('warbles), please let me know. And if you know any folks out your way who are wildlife rehabilitators, please ask them to keep an eye out for Cuterebra-infested sqs that they get in for rehab. Larvae should be removed (they can be carefully pulled out using forceps from a live squirrel through the hole they normally make in an animal's hide, and preserved in alcohol (isopropyl or ethanol). If I could get some photomicrographs of such larvae from western tree squirrels, we should be able to publish a paper about this since it would be a very unique situation.

So readers there you have it. Keep your eyes peeled and contact Frank if you see warbles on Western tree squirrels. (Don't bother him with eastern tree squirrels -- he already has plenty of bots from them.)


Beverly said...

Ugg...this whole conversation reminds me of the YouTube clip I accidently watched; of a woman with one in her head. To see a live thang living deep in a hole (in someone's HEAD) was enough to give me the heebie-geebies!

Okay, so I'm morbidly facinated by it too...and just watched another of some poor guy with 3-4 on his back. Lordy, they do leave HUGE holes...at least they close-up quickly when the thing is pulled out with tweezers!

You must just love yer job! :)

Camera Trap Codger said...

I agree. It's almost as good as science fictions when it comes to creeping people out.

Jackie said...

I didn't know we had bot flies in the U.S. interesting...do these bot flies also like humans? Or do only specific species go for humans?

Camera Trap Codger said...

I believe we have a lot of bot fly species, but none that normally parasitize humans. Occasionally a larva burrows into the wrong host, as it happened with the western gray squirrel I photographed last year.

Steve Bodio said...

WE find them in summer jackrabbits (black tailed)-- which is why we no longer hunt summer jacks. I suppose you could clean them off but too disgusting. Parasite bio & evo is both interesting and disgusting.

Owlman said...

In the late 40's my family lived in a tent in the summer and on the Bohan ranch(Cazadero,CA)in a small cabin with an out house in the winter. Great memories living off the land. We ate just about everything with some exceptions. On one ocassion I brought home a Black-tailed hare (Jackrabbit) but my father wouldn't use it for food because he said it was full of "Boils".
I know now that the boils were Bot fly infestations.