Pison is a cosmopolitan genus of wasps within the family Crabronidae. The genus comprises 145 described species, although many species, especially in South America remain undescribed. Distribution The genus is found throughout the tropical and warm temperate regions of the world, but does not extend into the more northerly temperate regions. Most species occur in the Southern Hemisphere, with a third of species occurring in Australia. This distribution pattern has been thought to indicate that the genus was once much larger, and has declined in the face of competition with more competitive wasp genera, leaving the genus largely concentrated in geographically-isolated regions. The habit of many species of building nests in holes in wood, keyholes, and similar situations has led to a number of species being distributed widely by ships and aircraft. Several species, including P. argentatum and P. iridipenne are of uncertain native distribution, having been dispersed by humans in antiquity. Biology Pison wasps raise their young on a diet of living, but paralysed, spiders. Spiders are collected by adult females, paralysed by means of a sting, and an egg is laid on the spider or spiders before they are sealed into a chamber constructed by the female. The paralysed spiders do not decay, and upon hatching the wasp larva eats the spider, before pupating and emerging from the chamber as an adult. While many species construct large mud nests in sheltered situations such as caves or tree hollows, other species make use of natural cavities such as hollow plant stems, beetle burrows, or abandoned bird nests, while still others dig their own nesting tunnels. Typically, multiple spiders-and-egg cells will be placed adjacent to one another in a larger nesting structure. Each cell is sealed off from adjoining eggs with mud or dung pellets. This sealing off of the young from each other is probably done to prevent competition and ensure that each young obtains sufficient food. Species and other subtaxa At one time the genus Pison was divided into the subgenera Pison, Pisonoides, Krombeiniellum, and Entomopison. These were later discarded in favor of species groups including (for the Americas): Conforme Fritzi Eremnon Delicatum Agile Stangei Krombeini Euryops Cressoni Chilense Convexifrons Pilosum Accepted species The following species are accepted : †Pison antiquum Antropov and Puławski, 1996 Pison argentatum Shuckard, 1838 Pison ashmeadi R.Turner, 1916 Pison assimile Sickmann, 1894 Pison atripenne , 1938 Pison atrum (Spinola) 1808 Pison auratum Shuckard,