The Nature Writers of Texas

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

Sunday, August 21, 2005

Millipedes are Gruesome but Harmless
by Ro Wauer

Summer rainstorms often produce more than just wildflowers and mosquitoes. Millipedes, also known as "thousand-legs" or "thousand-legged worms," also appear after these rains. They can be abundant, and in some areas they are so numerous that it is impossible not to run over many while driving down the highway. In the Texas Big Bend area, one researcher reported finding 1,302 millipedes per hectare. And after a drying period it is possible to find thousands of dried bodies, sometimes bleached white by the sun, on the roadways.

When crossing the roadway or crawling across any bare surface, they are much slower than they appear. They seem to be working furiously, their many legs going at an amazing speed. They actually "glide" over the ground, with successive waves of movement passing along the rows of legs, which alternately contract in groups and then spreads out. Although millipedes have a reputation for possessing hundreds, if not thousands, of legs, they lack that number by far. Two pairs of legs are attached to each segment that can number from 30 to 70 in adults, depending upon the species. One wonders how they can travel without stepping on their own toes. And when disturbed they curl up into a tight circle, leaving their hard upper surface exposed and keeping their soft underside protected.

Millipede sexes are separate. The reproductive organs are located at the anterior end of the body, between the second and third pair of legs; one or both pairs of legs on the seventh segment of the male are usually modified into copulatory organs. Females construct a dome-shaped nest of earth mixed with saliva, and she lays her eggs through a hole in the top, then sealing the nest with the same material. She may make several nests. The eggs hatch into larvae which usually have three pairs of legs, but segments and legs increase with each molt as the larvae grows. Millipede life span is only one or two years, once it reaches maturity.

Except in summer when the rains begin and they begin to wander, they mostly live in dark, damp places, well supplied with decaying vegetable matter on which they feed. They may even utilize living plant material, and some tropical species can feed on decaying animals. Although millipedes have very few predators, they are able to defend themselves by giving off an ill-smelling, yellowish fluid through openings along the sides of the body. Even the smallest individual is able to produce this strange odor. The fluid, similar to cyanide, is sometimes strong enough to kill insects placed in a jar with the millipede. And although the odor serves as a protection against predators, it does not hurt humans. Plus, millipedes cannot bite.

More than 150 species of millipedes have been identified in North America, but there are many more species that occur in the tropics. More than 6,500 are known worldwide; the largest is 30 millimeters (about one foot) while the smallest is only two millimeters in length. The long, reddish-brown species that occurs in southeastern North America, including the Texas Gulf Coast, is the banded millipede, known to scientists as Narceus americanus. Their closest relative is the centipede. Both are arthropods of the class Diplopoda, but neither is an insect.

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