Hi, Margaret Kramer & Ferret Folks,
 
The fly larvae you described on your neighbor's ferrets sound like warble
flies--I make that guess based on the vet's statement that the flies are
common on squirrels.  Warble flies and bot flies deliver eggs to the host
animal's skin surface, where the larvae hatch, burrow under the host's
skin, and feed on living tissue.  I agree with your evaluation: "ICK!"
The take-home message though, is, "Don't worry too much; these things are
rare in pet ferrets."
 
There are more kinds of warble flies west of the Rockies than in the rest
of North America, and I believe that their preferred hosts are rodents (not
cats, dogs, or ferrets); obviously, though, a few flies make host selection
mistakes now and then.  A vet visit is probably in order if you see a wound
that is not healing, or a fast-growing lump.  Warble fly larvae are
treatable, but can be life-threatening on a small animal if left untreated.
 
I'm writing this from memory at work, where I wear my microbiologist's
hat. My entomology hat is at home with my reference books, so if you
want more info, email me, and I'll look it up.
 
Bootsie (aka Rebecca Clayton; [log in to unmask])
[Posted in FML issue 1358]