Diplopoda

Diplopoda

Common names: millipedes, thousand-leggers, pill bugs

Probability of encounter: high

Quarantine importance: no known importance, although a few species are minor pests of crops and some produce poisonous or caustic defensive secretions. Some of the larger millipedes are used in the pet trade.

Similarity to mites: none, although many species have mites associated with them. Polyxenida are mite-size, but otherwise unlikely to be confused with mites.

Normal adult length: 2 mm - 28 cm
Body tagmata: head, trunk
Eyes: absent or 2-80 ocelli
Antennae: usually relatively short
Mouthparts: ectognathous mandibles with large 'cheeks', maxillae (gnathochilarium)
Legs: 3-numerous pairs
Respiration: 4 spiracles per diplosegment, opening on sternite near coxae
Gonopore: venter of 3rd trunk segment (behind 2nd pair of legs)
Distinguishing features: diplosegments each with two pairs of legs, second maxillae absent, 1st trunk segment (collum) legless

Many millipedes look as if they have thousands of legs, which gives this group its name and allows easy identification - at least of the larger specimens. All have distinct heads with antennae and elongate bodies with many segments having two pairs of legs (diplosegments). Body segments are added during development, so recently hatched individuals could be confused with springtails, insects, or mite larvae (6-legged) or with later stages of mites (8-legged).

First instar millipedes may have only 6 legs, and could be confused with insects or springtails (Collembola), but millipedes lack a distinct thorax. The minute species in the genus Polyxenus look very much like hairy beetle larvae and except for very young millipedes in other orders, are the only common diplopods in the microarthropod size category.

Diversity: perhaps 15 orders, >8000 spp.

References

Tree of Life - http://tolweb.org/tree?group=Diplopoda&contgroup=Arthropoda

Hoffman, RL. 1990. Diplopoda. pp. 835-860, in DL Dindal (ed) Soil Biology Guide. John Wiley & Sons: Brisbane.

Hopkin, SP and Read HJ. 1992. The Biology of Millipedes. Oxford University Press: Oxford.