Mollusks include snails, octopuses and squids, and bivalves (such as clams, oysters, and scallops). A few are venomous.
Cone snails are a rare cause of envenomation among divers and shell collectors in the Indian and Pacific oceans. The snail injects its venom through a harpoon-like tooth when aggressively handled (for example, during shell cleaning or when placed in a pocket). The venom can cause temporary paralysis that is fatal on rare occasions.
The California cone (Conus californicus) is the only dangerous mollusk in North American waters. Its sting may cause pain, swelling, redness, and numbness in the area of the sting and may rarely be followed by difficulty speaking, blurred vision, paralysis of muscles, difficulty breathing, and low blood pressure.
The bites of North American octopuses are rarely serious. However, the bite of the blue-ringed octopus—present in Australian waters—although painless, causes weakness and paralysis that may be fatal.
(See also Introduction to Bites and Stings.)
Cone snail stings can be immersed in hot water. First-aid measures seem to provide little help for injuries from California cone stings and blue-ringed octopus bites.
If people with any type of mollusk envenomation develop trouble breathing, immediate medical help should be sought.