Venom organ failure. Many caterpillars have defensive venom glands associated with specialized bristles on the body, known as urticating hairs, which can be lethal to humans (e.g., that of the "Lonomia" moth), although the venom's strength varies depending on the species. Bees synthesize and employ an acidic venom (apitoxin) to cause pain in those that they sting to defend their hives and food stores, whereas wasps use a chemically different alkaline venom designed to paralyze prey, so it can be stored alive in the food chambers of their young. The use of venom is much more widespread than just these examples.
Evolution of snake venom molecular history of snake venom have contradicted this, instead finding evidence of rapid adaptive evolution in many different clades, including the carpet vipers, "Echis", the ground rattlesnakes, "Sistrurus", and the Malayan pit viper, as well as generally in the diversification of PLA2 proteins. There is phylogenetic evidence of positive selection and rapid rates of gene gain and loss in venom genes of "Sistrurus" taxa feeding on different prey. Several studies have found evidence that venom and resistance to venom in prey species have evolved in a coevolutionary arms race. For example, wood rats of the genus "Neotoma" have a high