There are eleven families of wasps, split between the superfamilies Vespoidea and Apoidea. These are the Dryinidae, Embolemidae, Bethylidae, Chrysididae, Tiphiidae, Mutillidae, Sapygidae, Pompilidae, Sphecidae, Crabronidae and Vespidae. Most of the species are solitary and each family or group of solitary species specialises in a particular type of prey, e.g. flies, spiders, aphids, caterpillars. Some species do not build a nest for their brood but utilise natural crevices such as beetle borings, hollow plant stems or holes in masonry, while others excavate their own nests in suitable substrate such as dead wood or sand or friable soil. Prey is usually paralysed or killed by stinging and is then dragged or carried to the nest. Some species are cleptoparisitic on other species of wasps and so do not build a nest of their own, but lay their eggs in the nests of other solitary species. Some primitive species, after causing temporary paralysis of their prey by stinging it, lay their eggs directly on the bodies of the target host species. The host recovers and carries on with its normal behaviour but eventually dies due to the developing wasp. The more familiar social species construct their nests from chewed-up wood pulp and locate them underground, in hollow trees and roof-spaces. Others are hung in suitable trees and under eaves of houses. While most wasps hunt for suitable prey to either provision their nests or to feed directly to their young, the adults cannot digest large fragments of food material, as it will not pass through their narrow waist and into the digestive system. For this reason adult wasps exist largely on a semi-liquid diet consisting of nectar, honeydew, sap, or insect haemolymph. Hunting for prey and nest building is carried out by the females.