Earthworms are the largest and most numerous burrowing animals in New Zealand soils. But unless we disturb the soil, it is unusual to see them. We may see birds searching for them on the grass, or among garden litter and mulch. After rain we may see dead earthworms on a path: having emerged from their water-filled burrows they die of exposure to ultraviolet light.
The early bird …
A bird will hunt worms at dawn, when they are active near the surface (before the risk of the sun drying them out). Blackbirds watch for movement, often standing with their heads cocked. Seagulls ‘charm’ worms out by stamping on the ground. The worm may perceive the vibrations as raindrops, and come to the surface for moisture. It was once said that kiwi could smell worms, but it is now thought that they may pick up vibrations through sensors in their bill.
Yet earthworms are an essential part of our soils. Some inhabit litter and dung on the surface while others form almost vertical burrows and may live at more than a metre below the surface.
Worldwide there are about 6,000 species of earthworm, 1,000 of them native to Australia. The ‘Gippsland giant’ (Megascolides australis) is listed in the Guinness book of records at 3 metres long. A species in north-eastern New South Wales often grows to more than 1.5 metres, and is as thick as a garden hose. New Zealand’s longest worm grows to 1.3 metres.
Earthworms belong to a class known as Oligochaeta (meaning ‘few hairs’). This class in turn belongs to the phylum known as annelids (collectively called Annelida, from the Latin for ‘little ring’).
Other annelids are the marine polychaetes (‘many hairs’), and predacious or bloodsucking leeches (Hirudinea).