Hermit crab

Hermit crabs (ヤドカリ, Yadokari), a type of crab, are a bug that can be caught in. This bug can be caught in the Japanese-exclusive and in  on the Island.

Donating to the Museum
The hermit crab can be donated to the Museum by talking to Blathers.

In New Leaf
"Hermit crabs live in empty shells they can fit their bodies into. As they grow, they find bigger shells. They're quite picky about each new shell and first measure the opening with their claws. The shells they choose usually fit well, and they'll sometimes fight one another over ownership rights."

After being donated, the hermit crab can be found in the first room of the bug exhibit next to the pond.