March 30, 2007

Imagine a plague of gray squirrels descending on a community. The trees are brimming with rodents. There are 30,000 of them for every square mile. They swim through lakes and rivers, scramble across prairies and trot along fences.

The squirrel frenzy is not just a fantasy of the Camp Chicago journal. This actually happened in Racine, Wis., during three years in the mid-1800s.

"A Natural History of the Chicago Region," the terrific tome by Joel Greenberg, details these "mass movements of tremendous proportions." One observer described the horde:

"Near Racine, they were observed passing southward in very large numbers for two weeks, at the end of September and the beginning of October; and it was a month before all had passed. They moved along rather leisurely, stopping to feed in the fields, and upon the abundant nuts and acorns of the forests. So far had they departed from their accustomed habits that they were seen on the prairie, four or five miles from any timber; but even there, as usual, they disliked to travel on the ground, and ran along the fences wherever it was possible."

No one knows what caused these "crazed exoduses." Some believe it was because of acorn shortages. Others suggest overpopulation and disease.