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Invasion of the Squirrel Neuterers

Oct 23, 2009

A horror story was the last thing I expected when I recently picked up "By a Thousand Fires," an antique book about Ernest Thompson Seaton. But there it was, creepy and gross enough for a Hollywood thriller.

Seaton, who was sort of the Jeff Corwin of his day, devoted one chapter to debunking nature myths. One really hit home for me. Where I grew up in central Missouri, gray squirrels always outnumbered fox squirrels. Hunters, who generally favored the larger, meatier fox squirrels, had a gruesome explanation: gray squirrels sneaked into fox squirrel nests when the adults were away and castrated young male fox squirrels. That, they said, was why fox squirrel numbers were dwindling.

This always seemed a little far-fetched to me. For one thing, how would an animal with a brain the size of an acorn know how to perform surgery? Furthermore, why would a gray squirrel neuter his competitors when he could just as easily kill them-–male and female?

An equally good question might be how such an improbable myth gained such wide acceptance. Seaton had a more reasonable explanation. He grew up in Canada, where small, red squirrels outnumbered larger gray squirrels. Hunters there had the same incredible explanation for the imbalance-–red squirrels were neutering the grays.

Seaton noted that a species of parasitic botfly preys on squirrels, laying eggs in their groin. When the eggs hatch, the grubs burrow into the skin and consume the host animals’ testes or ovaries. Seeing the damage from these parasites, the average hunter had no way of knowing what caused it. Since hunters already were scratching their heads over the imbalance of gray and fox squirrels, it was a short leap of imagination to solve both riddles in terms of inter-species competition.

Reading this reminded me of a hunt awhile back, when I shot a young gray squirrel. When I claimed my prize, I was grossed out to find its carcass inhabited by two botfly larvae. The squirrel fell out of a tree and into in a creek, and the larvae wasted little time crawling out of the cold, wet body. I choked back my lunch and snapped this photo.

BotflyI have my own theory about why gray squirrels outnumber fox squirrels in some areas. In my experience, fox squirrels are most common in isolated woodlots. Grays are much more prevalent in large tracts of unbroken forest. It also seems to me that fox squirrels are more common in northern Missouri than in the Ozarks. Closer to home, I seldom see fox squirrels in the middle of the woods around our house. They generally appear near the edges of surrounding pastures. My conclusion is that grays, for some reason, are better adapted to deep forest than fox squirrels.

Would anyone care to venture a guess about what makes grays better woods squirrels? Or maybe share a nature myth or mystery?


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