Hedgehog caterpillar (Zoöl.), the hairy larvæ of several species of bombycid moths, as of the Isabella moth. It curls up like a hedgehog when disturbed. See Woolly bear, and Isabella moth. -- Hedgehog fish (Zoöl.), any spinose plectognath fish, esp. of the genus Diodon; the porcupine fish. -- Hedgehog grass (Bot.), a grass with spiny involucres, growing on sandy shores; burgrass (Cenchrus tribuloides). -- Hedgehog rat (Zoöl.), one of several West Indian rodents, allied to the porcupines, but with ratlike tails, and few quills, or only stiff bristles. The hedgehog rats belong to Capromys, Plagiodon, and allied genera. -- Hedgehog shell (Zoöl.), any spinose, marine, univalve shell of the genus Murex. -- Hedgehog thistle (Bot.), a plant of the Cactus family, globular in form, and covered with spines (Echinocactus). -- Sea hedgehog. See Diodon.