Moldworm

Quote from The Legend of Zelda: The Minish Cap Moldworm (モルドワーム, Morudowaamu) figurine:

"Appears in Minish roads. They come out of the ground when they sense prey. If you get swallowed, you’ll take damage and get all dirty!"

Moldworms seem to hold a symbiotic relationship with Pestos because when Link gets all dirty by being eaten by a moldworm, any Pestos in the area are attracted towards Link more quickly and attack more often as compared to when he is clean.