Forest Preserve District of Cook County, Illinois
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Ant Sanctuary
Nature Bulletin No. 17  June 2, 1945
Forest Preserve District of Cook County
Clayton F. Smith, President
Roberts Mann, Superintendent of Conservation

Cook County has an Ant Sanctuary! Out in the Palos, adjoining the forest preserve south of Sag Village, is a tract purchased a few years ago by the YMCA of Chicago for a camping center. It is rolling and mostly wooded with oaks, although there are a few small clearings including some open meadows in the low ground. bordering the oak woods at the edges of the clearings, and in the meadows, there are over 400 peculiar cone-shaped mounds, some of them seven feet in diameter and three feet high.

These are anthills housing huge colonies of a rare species of ant, Formica ulkei. The worker-ants are about one-fourth of an inch long with black or deep-brown heads and pale reddish-brown bodies. They have long legs, are very active, and bite viciously.

An observer watched the ants from one of these mounds going back and forth between the mound and an oak tree in a stream about 3 inches wide. Going up the tree, they went out to the leaves to "milk" the honeydew from a species of aphids or plant lice covering the under side of each leaf. The aphids feed on the sap in the leaves and secrete this honeydew.

Heavily laden, the ants returned to the mound over the same trail. Others were bringing in grasshoppers, caterpillars and small insects.

At the urgent request of scientists, the YMCA has placed small signs beside many of the mounds, stating that this is a sanctuary for this rare ant of special scientific interest, and requesting that the mounds be left undisturbed.

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