Spider wasps, also called pompilid wasps or spider-hunting wasps, are insects belonging to a diverse family named Pompilidae, of the order Hymenoptera.
Spider wasps are sometimes distinct from other wasps in features such as eye structure (no notch as in Family Vespidae), legs modified for grooming, and in having a groove dividing the mesopleuron (a region of the thorax) into halves. Larvae can also be identified by physical examination. Females are often larger than the males, with coloring and wing appearance varying greatly among the many species.
Spider wasps are long-legged, solitary wasps that use a single spider as a host for feeding their larvae. After paralyzing the spider with a venomous stinger, the spider is dragged to where a nest will be built – some wasps having already made a nest. A single egg is laid on the abdomen of the spider, and the nest – or burrow – is closed.
The size of the host can influence whether the wasp will lay an egg that will develop as a male, or an egg that will develop into a female – larger prey will result in the (larger) female. A complex set of adult behavior can then occur, such as spreading dirt or inspecting the area, leaving the nest site inconspicuous. When the wasp larva hatches it begins to feed on the still-living spider. After consuming the edible parts of the spider, the larva spins a silk cocoon and pupates – usually emerging as an adult the next summer. Some pompilids lay the egg on a still-active spider. In time, that spider will die, and the wasp larva begins to pupate.