Diplopoda

Millipedes are characterized by the presence of two pairs oflegs on most of the body segments, and they have numerous body segments. Mature forms vary from 10 to 100 mm long. They have two body regions, and they range in color from reddish orange to dark brown and black. Their reproductive organs are located on the ventral side, at the front of the body near the head. The head has two pairs of unbranched seven-segmented antennae and at least two pairs of mandibles, and eyes. Some species lack eyes, but have a dermal light sense. Spiracles leading into tracheae open above the coxae; the spiracles lack a closing mechanism. Repugnatorial glands may be present on the middle and terminal body segments. A mixture of hydrocyanic acid, iodine, and quinone is released from these glands, and sometimes it is discharged as a spray. One pair oflegs in the male is modified for mating. Two pairs oflegs per segment enable millipedes to exert considerable forward thrust. The leverage provided by the legs, together with the calcified head capsule, enables millipedes to force their way into a variety of habitats. They are able to penetrate between the fibers of rotting wood, the spaces in closely packed soil particles, and the narrow openings around doors and windows. The power for their pushing ability is achieved by the backstroke of the legs; it is longer in duration than the front stroke, and this generates more energy for forward motion.

Millipedes typically occur in moist or wet habitats. Many species curl into a sphere when disturbed, and others form a compact spiral. These behaviors provide some protection from predators, but are also effective in reducing water loss when they are in dry habitats. Food for millipedes is a variety of soft or decomposing plant material. They have been recorded as eating dead worms, mollusks, insects, and vertebrates. Several species are pests of field crops and in greenhouses. Millipedes comprise a proportion of the food of other animals, including toads and birds. Europe starlings (Sternus vulgaris)are especially destructive to millipede populations.

Mass migrations ofmillipedes have been reported, and this is sometimes accompanied by large numbers of centipedes. Masses ofindividuals can be involved, and their path may inter-ceptrailroad tracks, buildings, and agricultural fields. InJapan, Parafontaria laminata has been reported in mass migrations that seem to occur at intervals of 7 or 8 years. Other large populations include those ofGymnostreptuspyrrocephalus in South Africa (Natal) and Pseudopolydesmus serratus in the USA (Ohio). Mass movements may be stimulated by mating activity or features of the habitat, such as moisture and overcrowding, or to temperature and humidity changes. Rainfall causes migration of Unixenus nijobergi in Western Australia. In India, large aggregations and migrations of Streprogonopus phipsoni occur. Millipedes move indoors from habitats in the mulch and ground cover around urban structures, or move in large numbers from adjacent natural areas. Some species, such as Archiulus moreleti, are positively phototactic and are attracted to lights at night.

Mating is essentially the same for all millipede species; there is relatively little courtship and pre-mating behavior. The male transfers spermatic fluid to the genital orifice of the female and fertilization is internal. The genital openings ofmale and females are situated on the third segment, behind or on the second pair oflegs. During copulation the ventral surface of the terminal 13-14 body segments of the male is adjacent to the ventral surface of the anterior 10-11 body segments of the female. The seven anterior legs of the male are bent around the female. The region of the body segment 8-10 of the male is adjacent to the genital opening of the female, which is on body segment 3. Eggs are deposited singly in crevices in the soil or in a nest site and the female remains with the eggs for several days. The number of eggs deposited at one time and female fecundity vary among species. Some species lay about 20 eggs, while others lay up to 300; hatching occurs in 2-3 weeks. The immature stages develop through numerous molts, during which the number oflegs and the postcephalic body segments increase. Many species reach sexual maturity in 2 years; some require 4 or 5 years and then will live several years more.

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