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
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
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Update: June 2012