No-one has ever caught Giant Gippsland Earthworms (GGEs) in the act but it seems they like the lights out as it all appears to occur underground within their burrows. Each worm has both male and female sex organs. However, two worms are required for mating as they exchange sperm with each other. How they actually meet another worm and achieve this within the confines of their burrow is not known. Like most earthworms, they probably couple together, side by side in reverse position, aligning the male openings so they can exchange sperm. The sperm of the partner is stored in little chambers called spermathecae. When they are ready to produce egg cocoons, their clitellum (often called a saddle) swells in size and secrets the egg case and fluid that sustains the growing worm. The cocoon case slides slowly forward, picking up eggs and stored sperm as it moves over the head of the earthworm and eventually hardens. Fertilization occurs inside the egg cocoon. The breeding season occurs in spring and summer where breeding adults are recognisable by a large swelling that occurs near their head. Some earthworms can lay up to 1000 egg cocoons per year with many young in each cocoon. However, the GGE produce only one large, amber-coloured egg cocoon which can be as long as 9 cm. These are laid in special chambers that branch from their burrows, usually within 40cm of the soil surface. It is thought that it takes about 12 months for incubation to occur and the worm emerges from the cocoon when conditions are suitable. At around 20-30 cm, the baby is already on its way to becoming a giant.
Swollen clitellum thatsecretes cocoon
Growing worminside egg cocoon
Egg cocoon in soil chamber
Newly hatched GGE. Note the dark purple head andabsence of ditellum.