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Fall 2009

Urban Jungle

The changing natural world at our doorsteps | Illustration and text by Patterson Clark      

scratching squirrel

Flea infestation rates peak in February
at about 68 percent, soon after squirrel babies are born. The insects jump on and
off the mammal, so a cozy squirrel's nest may harbor a horde of fleas.

squirrel flea

December 15, 2009

Gray squirrels are hosts to irritating ectoparasites

"When you see a squirrel scratching, it's probably going after fleas," which tend to roam all over the animal, says Lance Durden, a Georgia Southern University entomologist who studies rodent ectoparasites. "But lice probably itch, too," he adds.

While cold weather suspends the activities of biting flies and mosquitoes, the flightless insect pests that torment wild mammals, including gray squirrels, are just beginning to enter their peak season.

Squirrel lice are most abundant in the winter, with infestation rates at about 100 percent. Why that rate drops to about 50 percent in July and August is unknown, but Durden thinks it may have something to do with hot weather and a squirrel's summer coat.

Durden once counted about 300 lice on one squirrel. The blood-sucking insects are concentrated mostly on a squirrel's head, shoulders and back of its neck — rarely on the belly, where the rodent can get at them with its teeth. Baby lice (nymphs) congregate on a squirrel's rump, where there is probably less competition from adult lice.

On the squirrel, female lice outnumber males, presumably because "females stay down close to their food source," says Durden. "Male lice are more vulnerable since they engage in risky behavior," clambering across the squirrel's fur to get at the females.

Durden assures us that "lice are quite host-specific, so there is no chance of squirrel lice infesting and feeding on humans."

Many flea species are a lot less picky about their meals. Bird fleas often feed on squirrels; and squirrel fleas feed on birds — and have been known to bite people, too.


From Vince Smith

An adult female Neohaematopinus sciuri, above, is a 2-millimeter-long sucking louse, one of three louse species found on gray squirrels.