Forest Preserve District of Cook County, Illinois
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The Constrictor Snakes of the Chicago Area
Nature Bulletin No. 693   November 10, 1962
Forest Preserve District of Cook County
Seymour Simon, President
David H. Thompson, Senior Naturalist

Snakes feed almost exclusively on other animals which they catch alive and swallow whole. A few eat the eggs of birds or turtles but they rarely touch anything that they find already dead. A snake's jaws are so loosely joined and its throat so elastic that it is able to stretch around prey large enough to form a big bulge in the stomach. The jaws with their backward-slanting teeth are slowly 'walked ' over the victim, one side at a time, like pulling a pillow case over a pillow.

Most kinds of snakes merely seize their prey and down it without any further ado. In contrast, a poisonous snake, for instance a rattler, stabs a rodent with its fangs and trails it until the venom takes effect. Still others, called constrictors, grab their victims, flip coils around them, and squeeze them to death. Four species with this feeding habit are found in the Chicago area -- bull snake, black rat snake, milk snake and fox snake.

These constrictors all have similar life histories. In early summer the females lay a half dozen to two dozen elongate eggs with white leathery shells. These are hidden under rocks, in rotten wood or in loose soil. They hatch in late summer or early fall. The young escape by cutting slits in the shell with an egg tooth on the tip of the snout -- like the egg tooth on the beak of a young bird. They become sexually mature in their second or third year but, unlike birds and mammals, they continue to grow throughout life. They spend the winter in hibernation hidden away below the frost line in burrows, under stumps, or deep in rock crevices.

The Bull Snake is Illinois' largest snake, sometimes reaching a length of six feet or more. One of these in a farmer's barn is more valuable than two or three cats for destroying rats and mice. In fields and woodlands they catch ground squirrels, gophers and young rabbits, or rob birds' nests both on the ground and in trees. One can consume a dozen duck eggs or mice at a single meal; or it can live for months without any food. A bull snake puts on a big show of ferocity when disturbed, but that is all bluff. With the raised head weaving from side to side, and pretending to strike, it hisses and snorts like an angry bull.

The Black Rat Snake also has the name Pilot Black Snake because it once was supposed to warn rattlesnakes of danger. This large snake spends much of its time climbing about in brush piles, bushes and trees -- often 20 or 30 feet above ground. The upturned ends of its belly plates enable it to hitch its way up smooth tree trunks and concrete walls. When surprised, it habitually "freezes" in imitation of a broken branch.

The Milk Snake, a medium-sized constrictor, is commonly found around farm buildings where it hides during the day and prowls at night. The superstition that it sucks milk from cows is absurd. Even supposing that it did like milk and could suck, no cow would hold still for that mouthful of needle-sharp teeth. Its diet is mostly mice and other snakes. The milk snake does not make a good pet because it has a mean disposition and is hard to feed. The King Snake, a downstate relative, is famous for strangling and eating rattlesnakes.

The Fox Snake is a rather large serpent with a disagreeable "foxy" odor when first captured. It hunts rodents, frogs, toads and salamanders on the ground, or climbs for birds and their eggs. At the Little Red Schoolhouse nature center, in recent years, two captive fox snakes have laid eggs from which, after being exhibited 7 or 8 weeks, foot-long young were hatched.

Because these constrictor snakes have a row of dark blotches down the back and buzz the tips of their tails when alarmed, they are often mistaken for rattlesnakes and ruthlessly destroyed. That is unfortunate. They are useful.

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