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Crustaceans

Crayfish

Seven species of crayfish are native to the Winnebago County region: the devil, digger, calico, northern clearwater and northern crayfish and the white river and prairie crawfish. They are all omnivores that eat plants, fish and carrion and are a critical food source for fish, marsh birds, snakes and turtles.

Crayfish gills must remain moist in order to take in oxygen, so the animals depend on groundwater and will burrow to reach it. “Primary” burrowers spend most of the year in burrows — some up to 9 feet deep — and emerge only to breed or forage. Their excavations produce chimneylike mounds of mud, which appear in fields in the spring. “Tertiary” burrowers live in streams and spend only short periods of time in burrows, such as during droughts. “Secondary” burrowers fall somewhere between the two, spending fair amounts of time in streams and burrows.

Crayfish begin life as fertilized eggs. Clusters of eggs attach to the female’s abdomen and remain there from several days to several weeks. During this time, a female is said to be “in berry.” Newly hatched young, which resemble smaller adults, remain on the female for a number of days while they molt and grow before becoming free-living individuals.

Like other arthropods, crayfish must molt in order to grow. Molting is a continuous process whereby a crayfish sheds its exoskeleton to allow its body to grow and then develops a new exoskeleton, which eventually hardens. Young crayfish may molt 14 times within their first year before they mature. Mature females then generally molt once a year; males, usually twice. Molting crayfish are vulnerable to predation because they are soft and slow.

Never release crayfish into a body of water they weren’t taken from. Many species of crayfish occur in very limited ranges, and so can be lost altogether when aggressive outsiders are introduced. One invader, the rusty crayfish, which was probably introduced by anglers dumping out unused live bait, has already displaced native crayfish from many waters in the northern half of Illinois.

Shrimp

At least one species of native freshwater shrimp lives in Winnebago County: the glass, or Mississippi grass, shrimp. Except for its eyes, it is completely transparent, and at times, recently ingested plants in its intestines give its abdomen a greenish tinge. It has long antennae and a laterally flattened body and resembles a much smaller version of marine shrimp sold in grocery stores.

Glass shrimp live in aquatic vegetation in lakes, ponds and backwaters. They eat algae, plants, and live and dead animals and are an important source of food for fish, especially small fish that also hide in vegetated areas.