You may go "erk" at a slug, or "eek" at a scorpion, but earthworms are loveable! They are the most familiar of all soil animals and especially valued by gardeners, farmers and fishermen. They are soft-bodied and divided into segments. They have no legs and move through soil by elongation of the front end into a soil fissure or between soil particles. Bristles on the outside of each segment hold the worm in place as muscular contractions ripple down the body, drawing the tail of the earthworm through the soil. Earthworms secrete copious amounts of slimy mucous to help them slide through the soil. These animals are large and strong enough to make their own tunnels through the soil.
Earthworm in a compost heap.
Some earthworms just eat their way through the soil or dung pats, absorbing energy and nutrients from the organic matter in the soil. Other worms drag dead leaves and bits of dung down into their burrows. Some expel their waste "casts" onto the soil surface while others do it inside their burrows.
Earthworm crawling across a cow dung pat - a good food supply.
It's obvious why fishermen like earthworms, but why do gardeners? By tunneling through soil, they make it loose and friable which makes it easy for roots to grow through. By dragging dead leaves into their burrows and eating it there, they are adding organic matter to the garden soil. This helps retain soil water and further breakdown of organic matter adds nutrients to the soil. Water can filter better down into soil if earthworm burrows are present.
Earthworm tunnels through soil. Note the root growing along tunnel in centre of photo.
Some worms live in the litter layers or the upper soil layers in the root zone where they make horizontal burrows to a depth of only 60 cm. Other earthworms live deeper in the soil and make vertical burrows to about 2-3 metres depth. But they make trips to the ground surface to feed on leaf litter.
Earthworms like moist soil. They can survive in dry soils but they are not active. However if the drought is severe, they will die. In dry conditions, they can burrow deep into the soil to 1 metre, tie themselves in a knot, secrete a coating of mucous about themselves which dries and helps prevent water loss. They also thrive in soils rich in organic matter. This is their food. Numbers of earthworms in agricultural soils in temperate Australia are around half the numbers of similar soils in Europe and New Zealand because Australian soils are mainly mineral soils with little organic matter and we have a drier climate.
After heavy rain, earthworms are often found wandering about on cement paths or on the ground as they get flushed out from their burrows. It's not the water that drives the worms to the soil surface as earthworms can't drown. It's the lack of oxygen in waterlogged soils that they can't tolerate.
Giant Worms! One native Australian earthworm is the giant Gippsland Earthworm which can reach to over a metre in length but an average worm would be 80 cm long and 2 cm in diameter. I have seen one estimate for length of the worm to be 4 m - stretched! It likes to tunnel into very moist soil in the banks of streams as it is vulnerable to desiccation. They burrow to 2 metres depth and live entirely underground but can be heard by the gurgling noise they make as they move in their mucous secretions.
Not a quirky bit! Earthworms can't regenerate once chopped in half with a garden spade. They simply die.