Millipedes: Diplopoda

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MILLIPEDES: Diplopoda

PILL MILLIPEDE (Glomeris marginata): SPECIES ACCOUNTS
FLAT-BACKED MILLIPEDE (Polydesmus angustus): SPECIES ACCOUNTS

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.

GEOGRAPHIC RANGE

Millipedes are found on all continents except Antarctica. Because they move so slowly on their own, most millipedes have small distributions. However, because many species are burrowers, they have been transported by humans throughout the world in soil and with plants. In fact, half of the species that are native to Britain have been introduced to North America this way. There are about seven thousand species of millipedes worldwide, with about fourteen hundred species in the United States and Canada.

HABITAT

Millipedes usually live in dark damp habitats, but Archispirostreptus syriacus and Orthoporus ornatus prefer dry habitats and live in deserts. Most species are under leaf litter, woodpiles, and stones. Soil dwellers are usually found in the top inch or two of soil. A few species climb trees. For example, some species of bristly millipedes live in the small cracks in tree bark. Although many millipedes are active at night, pill millipedes, such as Glomeris marginata, are usually active during the day.

DIET

Most millipedes eat decaying leaves and other vegetation, but some will eat shoots and roots of living plants. A few species are known to feed on animal remains or funguses. Many species will also eat their own waste pellets. It is believed that they obtain nutrition from funguses growing inside the pellets rather than from the waste itself.

BEHAVIOR AND REPRODUCTION

Most millipedes lack a waxy layer on the outside of their exoskeletons, or hard outer coverings, that helps to prevent the loss of body moisture. Like centipedes, millipedes spend most of their time in cool wet places and become active only at night or after rains.

Many millipedes defend themselves by rolling their bodies up into a ball or spiral. This behavior protects the legs and delicate underside of the animal, leaving only the hard plates of the body segments exposed. Some species also protect themselves by producing toxic or bad-smelling chemicals through a series of openings on the sides of their bodies. Some larger tropical species can actually squirt their attackers with a defensive spray. Bristly millipedes do not produce these defensive chemicals. Other species behave strangely when threatened. For example, Diopsiulus regressus alternates between flipping its body into the air and running short distances.

Males and females usually have to mate to produce offspring, with males usually depositing sperm directly into the reproductive organs of the female. There may or may not be any courtship behavior. Bristly millipede males must first spin a web on which they deposit their sperm. The female then approaches the web and puts the sperm into her own reproductive organs. In some pill millipedes a male coaxes a female to mate with squeaking noises made by rubbing the bases of his legs against his body. He then grasps the female's body with his legs. A sperm packet is released behind his head and passed back from one pair of legs to the next like a conveyor belt, until it reaches the reproductive organs of the female. In other pill millipedes the male covers the sperm packet in dirt before passing it back with his legs to his mate's reproductive organs.

WHY DO BLIND MILLIPEDES HAVE THEIR OWN NIGHT LIGHTS?

Scattered in the mountains of central and southern California are millipedes that glow in the dark. These eight species of Motyxia represent the world's only bioluminescent (BI-o-LU-mih-NEH-sent) millipedes. Bioluminscent organisms produce their own light. All but their undersides glow bright white, causing them to resemble small glow sticks. They do not have eyes to see approaching predators, but their obvious glow might warn nighttime predators of their bad taste.

Millipedes lay their eggs in the soil. Some species make individual cases for their eggs out of chewed-up leaves. In some species, the female, and occasionally the male, guards the eggs until they hatch. Although young millipedes resemble small adults, they are usually legless when they first hatch from the egg. After they molt, or shed their exoskeleton for the first time, they have six body segments and three pairs of legs. They add additional body segments and pairs of legs with each molt until they reach the maximum adult number. Millipedes molt in sheltered places underground or in cracks in the soil. Narceusamericanus and Orthoporus ornatus seal themselves off in special chambers dug for this very delicate stage of their lives. Millipedes reach adulthood in one or two years, sometimes longer. Adults live for one to eleven years, although some individuals may live longer.

MILLIPEDES AND PEOPLE

Millipedes are an important, yet seldom appreciated, group of animals that break down dead plants and recycle them into food for other organisms. It has been estimated that they add two tons of manure per acre (0.40 hectares) of forest floor each year.

Sometimes millipedes damage gardens and crops by eating shoots and roots. In Japan thousands of Parafontaria laminata crushed by trains have resulted in the tracks becoming slick, causing railroad cars to lose traction.

Some people have strong allergic reactions to the defensive chemicals of millipedes. The defensive fluids of Spirobolus will stain and irritate human skin, whether or not the person is allergic to the chemicals.

CONSERVATION STATUS

No millipedes are considered endangered or threatened.

PILL MILLIPEDE (Glomeris marginata): SPECIES ACCOUNTS

Physical characteristics: Pill millipedes are short and either dark brown or black. Their twelve body segments are dome-shaped in cross section. They have light brown or light gray margins toward the rear. Adults have seventeen to nineteen pairs of legs and reach 0.8 inches (20 millimeters) in length and 0.3 inches (8 millimeters) in width.

Geographic range: This species is found in the British Isles and in western and northwestern Europe.

Habitat: Pill millipedes are found in forests, fields, and gardens, usually in leaf litter. Unlike most millipedes, Glomeris marginata is better equipped to deal with drier conditions. It is often active on bright, sunny days.

Diet: Pill millipedes eat decaying leaves. A study in France showed that they eat about one of every ten leaves that falls to the forest floor each autumn.

Behavior and reproduction: When threatened they roll up into a ball, just like a pillbug. They also produce a chemical that makes them smell and taste bad to most predators (PREH-duh-ters), or animals that hunt other animals for food.

Males produce pheromones (FEH-re-moans), or chemicals that are attractive to females. They also make a squeaking sound to get females to mate with them.

Females lay six or seven dozen eggs in spring and again in summer. Each egg is deposited in a capsule. The young molt once inside the egg before they hatch about two months later. Cooler temperatures can delay hatching up to several months. The young take several years to reach adulthood. They may live up to a total of eleven years. Females may produce a dozen batches of eggs during their long life.

Pill millipedes and people: This species is important because it breaks down and recycles dead leaves and other vegetable matter.

Conservation status: This species is not considered endangered or threatened. ∎

FLAT-BACKED MILLIPEDE (Polydesmus angustus): SPECIES ACCOUNTS

Physical characteristics: Flat-backed millipedes resemble centipedes. The bodies of the adults are flat, dark brown, with about twenty segments. They measure 0.6 to 1.0 inches (14 to 25 millimeters) in length and are about 0.16 inches (0.4 millimeters) wide. The plate segments covering the back are ridged along their lengths. The antennae and legs are longer than in most other millipedes.

Geographic range: This species is found in northwestern Europe and was accidentally introduced to the southeastern United States.

Habitat: Flat-backed millipedes live in compost piles, under tree bark, inside cracks in stumps and logs, or in loose soil with lots of decaying bits of leaves.

Diet: They eat roots, dead leaves, and other bits of decayed plant materials, as well as strawberries and other fruits.

Behavior and reproduction: The ridged body of this millipede helps it to push its way through the soil.

Mating occurs from late spring through the summer and then again in late summer through mid-fall. Males usually mate only once. The females store the sperm from a single mating and produce several batches of eggs. Young millipedes hatching earlier in the year reach adulthood in one year, while those hatching later require two.

Flat-backed millipedes and people: This species has been studied by scientists to understand the effect of sunlight and day length on millipedes.

Conservation status: This species is not considered endangered or threatened. ∎