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 model described above, in which genes in other body tissues are duplicated and then recruited to the venom gland before natural selection for toxicity. However, in 2014 a new model was proposed in which salivary protein genes are duplicated and then restricted to the venom gland. This model does away with the recruitment hypothesis and cites the homology between certain venom and body genes as unrelated in the linear fashion described in the traditional birth-and-death model. Gene duplication is not the only way that venom has become more diverse. There have been instances of new venom proteins generated by alternative