Hi Mark,
The bots are in and around the groin, but lucky for the chipmunks they don't actually emasculate the host (as Fitch described in 1856 and Dury also promoted in 1898). This was a myth for a long time. Earnest Thomas Seton tried to question the myth in 1920 but it lived on. It does look nasty, and can't feel great with a maggot (or two or three) near your privates. But the testes are withdrawn into the abdomen during bot season, so it simply appears as if the bot has replaced the testes. The chipmunks go back to breeding once its over in about a month. (For chipmunks the bots enter after breeding season anyway-- at least in the north, with lots of time to recover). So bots are pretty well evolved to not impact the host. Recent authors have found no evidence for emasculation ( Bennett 1955, Siegmund 1964, Timm and Lee 1981 and 1982 and others).
Although... I have seen Peromyscus with nine C. fontinella at one time and they could barely walk, so when a heavy bot year they may make some individuals more likely to be caught by predators. But they can handle one or two bots with little or no impact. I have also removed one bot from a female mouse, which was preventing her from giving birth. But complications like this are rare.
If the animal allows the bot to develop and come out naturally, the wound heals very quickly. I have pulled bots ready to emerge from mice, and then caught the mouse again the next several days, and within about 2 days the wound looks like it had been stitched by a doctor, and a few days later it is hard to even find the wound. Some people think their may be special antibiotic and or healing properties in bots, because the wounds heal so fast. It is to the bots advantage not to hurt the host, as its offspring can use the same host the following years. Emasculating the host would also collapse chipmunk populations, which tend to breed only once in the north in most years. I have seen years with 80% infection rates, so this would put a lot of pressure on chipmunks if breeding came to a halt. Chipmunks tend to live a long time and defend territories so it would be hard for populations to recover if all of these were emasculated. So by not doing serious damage, C. emasculator ends up not doing a whole lot to impact chipmunk populations.
Thanks for the post. Hope this clears some things up. Still a great name.
Jeff