Millipedes' slow-crawling, rounded bodies have two pairs of legs on each body segment and rows of glands that secrete a pungent yellowish secretion when the millipede is agitated. This secretion is composed of organic chemicals called quinones, which make the millipedes distasteful to predators such as birds.
The Portuguese millipede naturally occurs in southwest Europe. They were first recorded in Western Australia around Roleystone in 1986 and since the late 1990s, have been found in other areas of south-west Western Australia. They are also found in South Australia, Australian Capital Territory, Tasmania and Victoria.
The smooth, cylindrical body of the Portuguese millipede distinguishes it from the native species around Perth, which have a bumpy look. Native millipedes are usually found in low numbers and are widespread. Portuguese millipedes congregate in large numbers and are quite mobile, especially after the first rains in autumn.
Portuguese millipedes will curl up into a tight spiral when disturbed, or try to escape with thrashing, snake-like movements. They are 20-45mm long with 50 body segments when fully developed. The adults range in colour from slate-grey to black. The juveniles are light grey/brown, often with a darker stripe along each side.
Portuguese millipedes reproduce in autumn and early winter. They would probably begin mating in March or April and lay most of their eggs in April and May. This would explain why they appear so mobile and so abundant after the first rains.
Mature females lay about 200 pinhead sized, yellowish white eggs in a small hole they have made in the soil. An immobile, legless stage hatches from each egg and develops into the first active stage of the life cycle after about one week. This first stage has only three pairs of legs, but each time the animal moults until it is mature, more legs and body segments are added.
Millipedes grow or develop through a series of moults. During moulting millipedes are very fragile because the new cuticle is soft and easily damaged when first formed. The millipede usually eats the old cuticle.
After the first year of life, juveniles have reached the seventh, eighth or ninth stage of development and will be about 1.5cm long. After this stage they will moult only in spring and summer. Portuguese millipedes usually mature after two years when they are in the tenth or eleventh stage of growth and some can live for more than two years.