The Nature Writers of Texas

The best nature writing from the newspaper, magazine, blog and book authors of the Lone Star State . . .

Sunday, August 05, 2007

Millipedes Love Our Wet and Warm Weather by Ro Wauer

Millipedes are far more numerous this late summer than at any time I can remember. They are not only crawling across the roadways but on the walls of my house and shed. As many as a dozen can sometimes be seen at one time. Although we humans may not appreciate all this rainy weather, apparently it is just right for millipedes. And I suspect that once our weather dries up a little that their numbers will increase even more, once they can crawl about without drowning.

Millipedes normally live in dark, moist places, as beneath logs and among piles of lumber and such, where they feed principally on vegetable matter, especially fallen leaves. Occasionally they will feed on roots of seedling plants. Like numerous other small creatures of dark, damp places, millipedes serve as one of nature's most important clean-up crews.

Almost everyone knows a millipede, although at times it becomes confused with the centipede. Millipedes are round, thick worm-like creatures that are tan to dark brown and divided into 25 to 100 segments. Each segment has two pairs of peg-like appendages that carry the animal over the ground. The twin-leg feature is reflected in the scientific name of the group, Diplopoda. There are about 6500 species worldwide, ranging from only about two millimeters to about 36 inches. Our local brown millipede rarely reached five inches in length. Sexes are separate, and the eggs, that are deposited in the ground in batches of 12 to 25, hatch into larvae with only three pairs of legs. They grow by molting, adding fresh segments each time, and may live up to seven years.

Centipedes, sometimes called "hundred-legs," possess a flattened body with fewer segments, each with a single pair of legs. Centipedes possess poison glands on the first pair of their sharp legs that are modified to form a hook-like jaw. Although the poison of North American centipedes is mild, unable to bother most humans, it is strong enough to subdue their prey. Some tropical species are far more toxic, however. Centipedes are reasonably fast and are able to run down their prey or to escape danger. The large tropical species, such as one Central American species that reaches ten inches, can catch lizards, mice and large insects.

The non-poisonous, non-predaceous millipedes use a very different tactic. When alarmed, rather than beating a fast retreat, they simply roll into a tight circle with their softer body parts protected inside. Their harder outer surface is made up of tough, calcium-rich exoskeleton that also allows them to burrow in the soil. In addition, millipedes possess a pair of glands on each segment that secrete an objectionable fluid that can be used for defense. Anyone handling these creatures more than just picking one up by its sides is sure to detect their lingering odor. Although the liquid is not dangerous, it can sting if it is somehow gotten in the eyes. And the tiny antennae carry numerous hairs that are olfactory in function.

Millipedes, along with the closely related sow bugs and pill bugs, are responsible for reducing about one-twentieth of the annual leaf fall into soils.

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