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Description

Venom is a secretion containing one or more toxins produced by an animal to cause harm to another. Venom has evolved in a wide variety of animals, both predators and prey, and both vertebrates and invertebrates. Venoms kill through the action of at least four major classes of toxin, namely necrotoxins and cytotoxins, which kill cells; neurotoxins, which affect nervous systems; myotoxins, which damage muscles. Venomous animals kill tens of thousands of humans per year. However, the toxins in many venoms have potential to treat a wide range of diseases.

Evolution

The use of venom across a wide variety of taxa is an example of convergent evolution. It is difficult to conclude exactly how this trait came to be so intensely widespread and diversified. The multigene families that encode the toxins of venomous animals are actively selected, creating more diverse toxins with specific functions. Venoms adapt to their environment and victims and accordingly evolve to become maximally efficient on a predator's particular prey . Consequently, venoms become specialized to an animal's standard diet.

Mechanisms

Venoms cause their biological effects via the toxins that they contain; some venoms are complex mixtures of toxins of differing types. Among the major classes of toxin in venoms are: Necrotoxins, which cause necrosis in the cells they encounter. Rattlesnake and viper venom contains phospholipase and trypsin-like serine proteases. Neurotoxins, which primarily affect the nervous systems of animals. These include ion channel toxins that disrupt ion channel conductance. Black widow spider, scorpion, box jellyfish, cone snail and blue-ringed octopus venoms function in this way. Myotoxins, which damage muscles by binding to a receptor, are small, basic peptides found in snake and lizard venoms. Cytotoxins, which kill individual cells, are found in the apitoxin of honey bees and the venom of black widow spiders.

Taxonomic range

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.

Arthropods

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