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.)