Backyard and Beyond

I believe these are Eastern Mud Snails (Ilyanassa obsoleta), which look like rocks until you look closer. There are quite a few of them in Jamaica Bay. And some of them were moving much too quickly. They were, in fact, hermit crabs, who use found snail shells for their own.Hermits don’t have protective shells like your usual crab species; they use snail shells instead, swapping to larger ones as they grow.This article argues that hermit crabs populations are going quite well because of a surplus of shells to choose from, from the introduced Common Periwinkle (Littorina littorea) which has spread up and down the East Coast. (Periwinkles generally like rocky shores, so the New York estuary doesn’t seem to have many of them.)I don’t know the species here. Anybody?

Hermit crabs from the Caribbean, rather larger than these, are exploited by the aquarium trade, and as a result, the internet is full of wails of children of all ages bemoaning their dead and dying “pets.” As animals wrenched from their own habitats (these are usually land crabs like the “Purple Pincher”), they potentially threaten local species and other crustaceans with diseases.