Irish Wildlife Photography: 2010

Friday, December 17, 2010

How Many Legs?

White-Legged Millipede (Tachypodoiulus niger)

The name millipede literally means 1,000 feet. In actual fact millipedes usually have between 36 and 400 legs, although one rare species has up to 750. This one, a white-legged millipede, (Tachypodoiulus niger – don’t you just love the way these Latin names trip off the tongue) has approximately 220 legs. They have two pairs of legs on each of the body segments, each of which is in reality a double segment. Millipedes moult several times as they grow, adding more segments and legs each time. The cast off skin is then eaten, thus restoring vital calcium supplies.

Millipedes belong to the Phylum Arthropoda and share the Subphylum Myriapoda with the centipedes. They make up the Class Diplopoda, characterised by two pairs of legs on each of the body segments. Millipedes can be easily distinguished from the somewhat similar centipedes (Class Chilopoda), which move more rapidly, and have a single pair of legs for each body segment. An estimated 10,000 species of millipede have been described worldwide and 41 species are known to occur in Ireland.

Millipedes are thought to be among the first animals to have colonised land. The oldest known land creature is Pneumodesmus newmani, a 1 centimetre long millipede, which lived 428 million years ago. It was discovered in Aberdeenshire in Scotland in 2004. Incredibly, the ancient forms of millipedes are nearly indistinguishable from certain groups living today.

Millipedes are vegetarians and feed on a wide range of plant material, especially when it is soft and decaying, although they sometimes eat dead invertebrates, such as worms and insects. They are usually found under leaf litter or stones, or in the soil and compost heaps. They can play an important role in enhancing the decomposition of dead plant material. Most millipedes have ocelli (eye spots) on the head. They have short antennae with which they constantly tap the ground as they move. They are usually found in damp places as they are prone to desiccation and avoid light. They are more active at night.

Tachypodoiulus niger is relatively common and occurs in Ireland and the UK as well as most of continental Europe. It is especially common on chalky and limestone soils. It lives in leaf litter, under bark or in moss, and feeds on algae, detritus and sometimes soft fruit such as blackberries. Predators include centipedes and hedgehogs. Tachypodoiulus niger is most active at night but during the summer it also becomes active in the afternoon.