Venomous animals
Venom is a form of toxin secreted by an animal for the purpose of causing harm to another.
The potency of different venoms varies; lethal venoms are often characterised by the median lethal dose (LD50, LD50, or LD-50), expressed in terms of mass fraction (e.g., milligrams of toxin per kilogram of body mass), that will kill 50% of the target of a specified type (e.g., laboratory mice).
Utilization of venom across a large number of species demonstrates an example of convergent evolution and a homoplastic trait. 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 on, 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 (particularly the precise ion channels within the prey). Consequently, venoms become specialized to an animal’s standard diet.
Venomous animals resulted in 57,000 human deaths in 2013, down from 76,000 deaths in 1990.
Venomous invertebrates include spiders, which use fangs — part of their chelicerae — to inject venom (see spider bite); 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 Polistes fuscatus, the female continuously releases a venom that contains a sex pheromone that induces copulatory behavior in males. In Polistes exclamans, venom is used as an alarm pheromone, coordinating a response with from the nest and attracting nearby wasps to attack the predator. In Dolichovespula arenaria, the observed spraying of venom out of their sting has been seen from workers in large colonies. In other cases like Parischnogaster striatula, the venom is applied all over their body in order to make themselves immune to certain harmful diseases. Some cases like the venom from Agelaia pallipes have significant inhibitory effects on essential biological processes like chemotaxis and hemolysis which can lead to organ failure. This prevents the spread of disease throughout the colony.
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