#batillaria

One of Australia’s five Batillariids - and one of those was accidentally introduced from New Zealand.

That said, B. australis is out-of-place too - it’s native to the east coast of Australia. There used to be a South Australian population, now extinct. And about 60 years ago they turned up in the Swan River here in Perth, and they’ve completely taken over. Estimates suggest 3.6 billion of the little buggers in the Swan Canning Riverpark, and they’re out in Cockburn Sound too, which is where I found these two. At the beach beside UWA, they were literally piled up in their hundreds.

To add further notoriety, they’re a host of the parasitic fluke Austrobilharzia. The larvae of these trematodes are ejected from the snail, and they have to find the legs of a wading bird to drill into. But since they are animals of very little brain, they apparently think that humans are actually wading birds, drill in, and are promptly killed. The ongoing immune reaction as your body try to destroy the dead invader produces the condition known as ‘Swimmer’s Itch’.

They aggregate on mud or muddy sand in well-sheltered areas such as mangrove swamps and in the mouths of coastal lakes, where organic detritus settles easily. They prefer areas above mid-tide, where they leave a maze of feeding tracks crawling over the surface. They were an important seafood for native peoples of the east coast, and the shells are common in middens.