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Meet the Botfly

Squirrels with Barnacles?

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Mrs. Stacy Wood's two cats, Martha and Lula, watch squirrels covered with "barnacles."

By Sherry Kughn
JSU News Bureau

25 October 2004 — Jacksonville State University employee Stacy Wood opened the glass sliding door at her Talladega home one morning so her cats Martha and Lula could watch the squirrels. She saw squirrels covered with barnacle-like growths on their heads and backs frolicking in her cedar bird feeder.

Intrigued, Mrs. Wood took pictures. Squirrel hunters in the area are probably familiar with the phenomena that Mrs. Wood found out later was an infestation of bot flies, or to be more accurate Cuterebra emasculator Fitch, which, according to Dr. Cole Benton, JSU zoologist, look like “a stream-lined bumble bee.”

The bot flies lay eggs throughout the summer. During late summer or early fall, the eggs become larvae and crawl into the noses, ears, or other orifices of squirrels, burrowing into the animal’s muscles and emerging beneath the skin. The process creates a brown-colored lump called a warble and is about the size of a penny. Then they eat a tiny hole in the middle of the lump to breath.

“They last a few weeks,” said Dr. Benton. “Then the larva crawls out and pupates in ground litter.”

The bot fly pupa stays dormant for the winter and emerges as a fly in the spring.

Mrs. Wood was worried about her cats, “two spoiled-rotten pets who live indoors.” She worried unnecessarily, though, because the chance of her pets becoming infected is rare. Pet owners whose animals live outdoors, though, and even people who climb trees, such as children or tree cutters, have been known to become infected with the larvae of the bot fly.

“These are accidental cases of myiasis, which is an infestation with larvae,” said Dr. Benton. “Usually larvae are very selective of where they lay their eggs and of whom they choose as hosts.”

If the larvae infect the wrong hosts, usually the larvae do not survive, said Dr. Benton, and they rarely complete their life cycle in humans or pets. Even for the unlucky squirrels or rabbits, the long term effect is usually minimal, he said.

After the larvae exit, the skin shrinks and returns to normal. The animals that get them, said Dr. Benton, might become sterile if the larvae get into the scrotum. In the worst case scenario, a bacterial infection from the larvae can spread throughout an animal whose immune system might be weakened by the infestation. Death could result.

A website that tells all about bot flies is, which is sponsored by the University of Florida in Gainesville, Fla. Its authors state that squirrels are probably uncomfortable while infected, but transporting them to a veterinarian to surgically remove the warbles would cause the animal more stress than allowing nature to take its course.

(University of Florida photos used with permission.)

Sherry Kughn can be reached at

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