Venom types. Among the major classes of toxin in venoms are: Venom is widely distributed taxonomically, being found in both invertebrates and vertebrates; in aquatic and terrestrial animals; and among both predators and prey. The major groups of venomous animals are described below. Venomous arthropods include spiders, which use fangs — part of their chelicerae — to inject venom; and centipedes, which use forcipules — modified legs — to deliver venom; along with scorpions and stinging insects, which inject venom with a sting. In insects such as bees and wasps, the stinger is a modified egg-laying device — the ovipositor. In
Evolution of snake venom and that there may be significant variation in the selection pressure upon various snake venoms. Snakes use their venom to kill or subdue prey, as well as for other diet-related functions, such as digestion. Current scientific theory suggests that snake venom is not used for defense or for competition between members of the same species, unlike in other taxa. Thus adaptive evolution in snake venom has resulted in several adaptations with respect to these diet-related functions that increase the fitness of the snakes that carry them. Venom that is toxic only to a certain taxon, or strongly toxic only to