Millipedes: Diplopoda - Physical Characteristics

Millipedes usually have long wormlike bodies that measure 0.08 to 11.8 inches (2 to 300 millimeters) in length. However, bristly millipedes resemble small (0.16 inches; 4 millimeters) caterpillars that are covered with tufts of stiff hairlike structures. Pill millipedes have short wide bodies that roll up into a ball just like pillbugs. Most millipedes are brownish, blackish, or dark greenish, but many are pale or pinkish. Others are brightly marked with yellow or red. The head has two pairs of jaws. The eyes, if they have any at all, are simple and have only one lens each. The antennae (an-TEH-nee), or sense organs, are short and seven-segmented.

The usually stiff bodies of millipedes are either flattened, rounded, or dome-shaped in cross-section and divided into eleven to 192 segments, depending on age and species. Each segment is formed while the millipede is still in the egg by the joining of two body segments. This is why most of the body segments have two pairs of legs. The first and last body segments are always legless. The first legless segment is a heavily armored collarlike segment that separates the head from the rest of the body. Segments two through four have one or two pair of legs each, except in the males of one group of millipedes where these legs are specialized and used for reproduction. Adults have anywhere from eleven pairs (twenty-two legs) to 375 pairs (750 legs) of legs. Males and females look very similar to one another, but males usually have longer legs so they can grasp the female while mating. The legs of millipedes are attached directly underneath the body and are only slightly visible on the sides, if at all. This arrangement gives them the power they need for burrowing and allows them to get into narrow spaces without breaking off legs. The common name millipede, meaning "thousand-legger," refers to the fact that millipedes often have a lot of legs and not to a specific number.