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 recent lineage was correlated with a shift to a diet of vertebrates. Despite the higher toxicity of the venom of arthropod-consuming species, it was not found to incapacitate or kill prey any faster than that of species with fewer arthropods in their diet. Thus, the venom is thought to have evolved to minimize the volume required, as the production of venom carries a significant metabolic cost, thus providing a fitness benefit. This pattern is also found in other lineages. Similar results were obtained by a 2012 study which found that the venom of arthropod-consuming "Echis" species was more toxic to