Sphecid wasps range in size from 9 to 51 mm (0.4 to 2.0 in) long. They may be black, black and red, yellow and black, or white and black; some are tinged with metallic blue or green. Sphecid wasps prey on a wide variety of insects, including cockroaches, caterpillars, bees, grasshoppers, flies, spiders, beetles, crickets, ants, and leafhoppers. Sphecids hunt to provide for their young. The female wasp's sting can inflict a painful wound in defense, but in general they are shy creatures and pose no threat to humans.
Sphecid wasps are solitary wasps-that is, the females independently construct and provision their own nests. Many nest in hollow twigs, but most dig their nests in the ground, especially in sandy places. Some species nest together in aggregations of thousands of individuals. Adults are active in sunny places and are often seen on flowers, which they visit to drink nectar. Velvet ants, cuckoo wasps, and parasitic flies, often invade the nests of sphecid wasps and consume the wasp larvae or the larvae's provisions. Sphecids are closely related to bees, and scientists believe that the two groups evolved from a common sphecidlike ancestor.
Among the best known sphecid wasps are the thread-waisted caterpillar hunters. Female caterpillar hunters close their nests with soil while they are hunting for food. They utilize such landmarks as rocks and twigs to relocate the entrance when they return. The hairy caterpillar hunter sometimes tamps the soil with pebbles to compact it when closing the nest entrance. An account of this wasp's behavior, published in 1898 by George Peckham, a Milwaukee schoolteacher, was the first description of an insect using a tool. It caused a debate among scientists because at that time only humans were believed to be tool users. It is now known that many insects and other animals also use tools.
Sphecids called sand wasps hunt flies. Dead flies would rot if they were stockpiled for the larva. As a result, sand wasps provision their nests progressively, bringing fresh flies as needed. These wasps burrow in sandy soil. Some species nest only in the loose, blowing sand of dunes.
Another well-known sphecid wasp is the giant golden sphecid. This colorful species is reddish with golden hair. It provisions its nest with crickets.
Scientific classification: Sphecid wasps comprise the family Sphecidae in the order Hymenoptera, which also includes other wasps, ants, and bees. Sand wasps are in the genus Bembix. The best known species of caterpillar hunters are in the genus Ammophila. The giant golden sphecid is Sphex ichneumonius.