The Room 3 class at North East Valley Normal School asks :-
On a class insect hunt we found a large slug which appeared to be laying eggs out of the side of its head. Is this what was happening?
Hamish Spencer, a zoologist at the Univeristy of Otago, responded.
Land snails and slugs that are found in New Zealand gardens, playgrounds and farms are nearly all kinds that were brought here accidentally from Europe. Native species are mostly restricted to native bush.
All but a handful of both introduced and native forms belong to a group called pulmonates, which means they breath with a lung. This lung opens to the air via a small hole, called the pneumostome, a sort of closeable nostril. You can often see the pneumostome wide open on the back of a relaxed slug, about half way along, or near the shell's mouth on the back of a garden snail. In addition to this lung, pulmonates have several other features that allow them to live on land. For example, they all produce large amounts of mucous that prevents their bodies from drying out.
All pulmonates are both male and female; scientists who study animals (zoologists) say they are hermaphrodites. Slugs and snails have a second hole, called the gonopore, which is found on the side of the body near the base of the right eye's tentacle. The gonopore is smaller than the pneumostome and you need to look more carefully for it. Slugs and snails lay their eggs through the gonopore. So, yes, your slug was laying eggs out of the side of its head.