We examined field distributions of the scavenging snail Amphissa columbiana and looked for evidence of fish predation. In the laboratory, we tested for predation by 6 crab and 10 sea star species and measured the ability of A. columbiana to chemically detect and respond to the sea star Leptasterias hexaclis. A. columbiana occurred from the low intertidal zone to depths of at least 92 m. We found no evidence of fish predation, but 4 crab species readily fed on A. columbiana. Only 3 of 10 sea star species fed on A. columbiana and predation rates were low. The inability of many sea stars to prey on A. columbiana was related to an unusual defense in which the snail inserted its proboscis deep into one of the sea star's ambulacral grooves and bit the radial nerve. The injury, which generally repelled the attacking sea star, immobilized the affected arm, rendering it useless for several days. The biting defense appears to be effective against several sea star species and may reduce predation on A. columbiana.