A University of Georgia
Extension Service colleague
forwarded this query about a mysterious squirrel disease:
“I live in Midtown (a neighborhood in Atlanta), and
some of the squirrels that
frequent my bird feeder have big and small lumps on their
backs, throats and bellies. I’ve
seen both male and female squirrels with these thick, tumor-
looking lumps. … It’s
disconcerting because there are several like this, and I
wonder if they’re breeding and
spreading this disease, whatever it might be. Secondarily, I
worry about my cats which sit
in my windows. Anyway, should I be concerned? I actually
like squirrels, and I hate to see
the little guys looking so pitiful.”
Those “tumor-looking lumps” on the squirrels are almost
certainly the larvae
of Cuterebra emasculator — a bot fly.
| Sorry, no 200 dpi
image available  Photo courtesy University of Florida .htm |
Of the array of parasites that squirrels endure, Cuterebra
produces the most questions.
Usually it’s squirrel hunters who notice these lumps and the
stout, black maggots that
inhabit them.
The hunters often call them “warbles or wolves.” They ask
what they are and
wonder if it is OK to eat the meat of such squirrels. (The meat
is OK, and when the
squirrel is skinned the parasites come off with the hide.)
The Cuterebra has an interesting life cycle. The adult fly
lays its eggs on the
squirrel or at a site squirrels frequent. Other Cuterebra
species may infest rabbits or
other species of rodents.
After the maggot, or larva, hatches, it crawls onto the
squirrel and enters the flesh,
possibly through the nose. Then it burrows to a place, often on
the neck or back, where it
grows to a size that can be seen.
The feeding end of the larva penetrates into skin, and the
rear end is exposed to the
outside. Spiracles in the maggot’s rear end are like portholes.
They are the exposed ends
of the air tubes through which the maggot breathes.
Can these flies infest the cats or humans? It’s extremely
unlikely. The regular hosts
of Cuterebra emasculator are gray squirrels and
chipmunks. It’s pretty hard for a
parasite to change its evolutionary genetic program and
parasitize something new.
However, Curtis Sabrosky, an authority on members of the
Cuterebra group, did report in
his 1986 book that a few human infestations have occurred.
So what should we do about this “problem”? Mostly nothing, in
my view. Just
watch the squirrels and enjoy knowing more about their life and
times.
Soon, as cold weather approaches, the larvae will mature.
When their days as a maggot
are done, they will withdraw their mouthparts from the squirrel
and worm their way out of
the little sack the squirrel has grown around them. Then they
will drop to the ground to
pupate. Next year, the adult flies will emerge to repeat the
cycle.
Are these parasites “bad”? No. Like a lot of things in the
natural world,
they just are.
