Numerous animal species naturally produce chemical toxins which are used to kill or incapacitate prey or as a defense against predators. Venomous animals deliver these toxins as venom through a bite, sting, or other specially evolved mechanism. Poisonous animals, on the other hand, contain or secrete toxins and do not actively deliver them. This list deals exclusively with the former. Venoms have evolved to serve a wide variety of purposes. Their intended effects can range from mild fleeting discomfort to paralysis and death, and they may be highly selective in which species they target, often making them harmless to all but a few specific co-evolved organisms; what may be fatal to one species may be totally insignificant to another species. Because the definition of "venomous" can be extremely broad, this list includes only those animals with venom that is known or suspected to be medically significant for humans or domestic animals.
Invertebrates
Arachnids
Strictly speaking, all spiders and scorpions possess venom, though only a handful are dangerous to humans. Spiders typically deliver their venom with a bite from piercing, fang-like chelicerae; scorpions sting their victims with a long, curved stinger mounted on the telson.
The remipedeXibalbanus tulumensis is a centipede-like crustacean that lives in underground anchialine caves of Mexico and Central America. Although blind, it is a formidable predator and feeds on the shrimp that share its underground pools.
Mollusks
Cone snails of the family Conidae are a diverse group of predatory marine gastropods, mostly tropical in distribution, which hunt and immobilize prey using a modified harpoon-like radular tooth that can deliver neurotoxic conopeptides. All cone snails are venomous, though the danger posed to humans varies widely by species.
Cnidarians
Jellyfish sting using microscopic cells called nematocysts, which are capsules full of venom expelled through a microscopic lance. Contact with a jellyfish tentacle can trigger millions of nematocysts to pierce the skin and inject venom.
Many species of octopus, squid, and cuttlefish make use of venom when hunting their prey.
The blue-ringed octopodes produce tetrodotoxin, which is extremely toxic to even the healthiest adult humans, though the number of actual fatalities they have caused is far lower than the number caused by spiders and snakes, with which human contact is more common.
Vertebrates
Fish
There are at least 1,200 species of venomous fish, including:
Though there are numerous poisonous amphibian species capable of secreting lethal toxins through their skin, relatively few amphibians are truly venomous.
Only a few modern mammal species are capable of producing venom; they are likely the last living examples of what was once a more common trait among the mammals. The definition of "venomous" becomes less distinct here, however, and whether some species are truly venomous is still debated.
