Illinois Natural History Survey - University of Illinois

Species Spotlight: Millipedes

Susan Post

Millipedes are one of the few life forms that can give us a flashback glimpse of early life. Century after century, eon following eon, they have survived, coming down to the present day almost unchanged. Occupying dark moist habitats, they are seldom seen except on rainy days, perhaps crossing a wet log. In more pleasant weather, if someone happens to roll over a millipede's log home, the creature will be revealed slowly moving away from the disturbance.

Millipedes belong to the class Diploda, which literally translated means "thousand legs," although they never have that many. Millipedes have a long, cylindrical, segmented body that has 25 to 100 segments. Two pairs of legs are found on each body segment except for the three segments following the head. These segments, called the thorax, have only one pair of legs per segment. Despite their many legs, millipedes move very slowly. Their bodies are adapted for pushing through decaying leaf litter and burr-owing into the soil, not for sprinting. They glide slowly, successive waves of movement passing along rows of legs.

Due to the their slow movements, millipedes would be an easy target for predators if they didn't have several means of defense. When disturbed, they curl themselves into a tight spiral with the head, numerous legs, and the vulnerable body parts in the center of the protective casing. If this does not deter predators, the millipedes also have a system of chemical warfare. When threatened, a millipede can discharge an obnoxious toxic liquid containing hydrocyanic acid from a row of glands along each side of its body. Despite these defensive adaptations, shrews do not hesitate to eat them, and in some forest habitats millipedes make up the bulk of a shrew's diet.

Millipedes are found throughout Illinois, living among leaf litter, under bark, or in rotting logs. During dry weather they may burrow into the ground. Millipedes are vegetarians, feeding chiefly on decomposing plant tissues.

Female millipedes have very little maternal instinct. Once the female lays her eggs in the ground, enclosing them in an earthy capsule, she leaves. When the young hatch they have six segments and only three pairs of legs and resemble wingless insects. The young grow in length by molting. With each molt the millipede will add three or more segments and additional legs. Millipedes have a life span of two to seven years.

Creatures like the millipede, with its multitudes of legs, may seem unpleasant to some people, but they are not dangerous. The gentle millipede does not bite and it performs a valuable service for humans: it is one of nature's best composters--eating decaying plants and returning the organic matter to the soil.

milli.gif
The millipede Narceus, pictured here, is the largest millipede in the state, 
sometimes reaching a length of 5 inches. (photo by Michael Jeffords)
 


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Subject: INHSPUB-2160
Last Modified 3/19/96



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