Centipedes and Millipedes

Centipedes and millipedes are somewhat similar organisms. Together, they make up approximately twelve thousand species of long, flattened, segmented animals, grouped among the Myriapods. A major difference between centipedes and millipedes is diet. Centipedes are carnivores, living on other animals, and millipedes are herbivores, living on dead plant matter. Millipedes have cylindrical bodies, while centipedes are wormlike. Whena centipede or millipede runs, it picks up each leg, one after the other. However, it only moves the legs on one body side at a time. The result is that legs move in rhythmic waves along the body. Millipedes are much slower than centipedes.

Physical Characteristics of Centipedes
Centipedes belong to the class Chilopoda of the phylum Arthropoda, which includes insects, myriapods, crustaceans, and spiders. Centipedes resemble worms. Their heads contain paired, jointed, sensory antennae; brains, connected to ganglia; compound eyes, simple eyes, or no eyes at all. Centipedes also have two pairs of jaws. The first pair are toothed mandibles and the second pair, the underjaws, have palps. A centipede body is divided into between twelve and one hundred segments, each having two legs, so the name "centipede", which means "hundred-footed", is appropriate. The first pair of legs, in the segment behind the head, holds poison claws that are used to fight or kill prey. These claws are full of a venom made in the head. Each of the paired legs in all segments but the last one are shorter, of similar length, and clawed. Those in the last segment are longer than the others.Athin, tail-like cercus projects from a centipede's rear. Centipedes breathe through air tubes (tracheas) on the sides of their bodies.

The Lives of Centipedes
Centipedes are carnivores that eat worms and insects, which they poison. Nocturnal, they hide under stones, logs, or ground litter during the day. Some species bear live young, but most lay eggs. Small centipedes of temperate climates (such as the United States) are harmless to humans. Larger, tropical centipedes are much more dangerous, as exemplified by the families Scolopendridae, and Geophilidae. The reproductive cycle of centipedes often begins in spring or fall, when a male places his semen on the ground. In the spring, a female puts the semen inside her body, immediately using it to fertilize her eggs. If the female takes in the semen in the fall, she may carry the semen for months before fertilization occurs. After fertilization, females lays their eggs, which hatch in two to four weeks. Newborns have smaller numbers of segments and legs than adults. They grow by molting. After each molt, new body segments and legs are produced. Mother centipedes tend their young until they can hunt. Centipedes mate at two to three years old and may live for six to ten years.

Centipedes Large and Small
Scutigeridae have compound eyes, long antennae, and fifteen pairs of long legs. Found in Europe and the United States is a two-inch species with a brown, striped body, the common house centipede. Lithobiidae, stone centipedes, are also short-bodied. They and scutigerids are the fastest centipedes. Stone centipedes have simple eyes, the same number of legs as scutigerids, and antennae about 35 percent the length of their bodies. Neither family delivers stings harmful to humans. Scolopendridae have over twenty pairs of legs, short antennae, and simple eyes or none at all. These slow-moving, tropical centipedes are the largest species, reaching lengths of one foot. The fourth family, Geophilidae, known as soil centipedes, are also slow moving. They have up to 350 legs, short feelers and no eyes. They burrow in the ground. Scolopendrids and geophilids deliver bites harmful to humans.

Millipedes
Millpedes are arthropods of the class Diplopoda and occur worldwide, except for polar regions. They are 0.1 to 12 inches long. The largest American species, the four-inch, red and black Narceus americanus, lives in southern forests. Millipede heads are round and hold a pair of short antennae, two simple eyes (or no eyes), and mandibles. "Millipede" means "thousandfooted" but none have over five hundred legs. The legs arise from the characteristic feature of diplopods, 9 to over 110 diplosomites. These double trunk segments form by the fusion of two body segments. Each diplosomite holds two pairs of legs, except for the legless head segments and the next three segments, each with one pair of legs. Every four-legged diplosomite contains two pairs of ganglia and two pairs of heart arteries. Millipedes grow in length and diplosomite number by molting. They live one to seven years and reproduce by laying eggs. Millipedes are covered with thick, calcified chitin back plates. Their protective strategy, when threatened, is to curl into a ball with their head inside and excrete a smelly, toxic liquid from "stink glands." This liquid kills or repels predators. Millipedes inhabit dark, damp places and eat decaying- or in some cases live-plants. Their actions damage some crops but, more often, enrich the soil.