Wasp
The largest social wasp is the Asian giant hornet, at up to in length. The various tarantula hawk wasps are of a similar size and can overpower a spider many times its own weight, and move it to its burrow, with a sting that is excruciatingly painful to humans. The solitary giant scoliid, "Megascolia procer", with a wingspan of 11.5 cm, has subspecies in Sumatra and Java; it is a parasitoid of the Atlas beetle "Chalcosoma atlas". The female giant ichneumon wasp "Megarhyssa macrurus" is long including its very long but slender ovipositor which is used for boring into wood and inserting eggs. The smallest wasps are solitary chalcid wasps in the family Mymaridae, including the world's smallest known insect, "Dicopomorpha echmepterygis" (139 micrometres long) and "Kikiki huna" with a body length of only 158 micrometres, the smallest known flying insect.
Parasitoid
Within the Hymenoptera, parasitoidism evolved just once, and the many described species of parasitoid wasps represent the great majority of species in the order, barring those like the ants, bees, and Vespidae wasps that have secondarily lost the parasitoid habit. The parasitoid wasps include some 25,000 Ichneumonoidea, 22,000 Chalcidoidea, 5,500 Vespoidea, 4,000 Platygastroidea, 3,000 Chrysidoidea, 2,300 Cynipoidea, and many smaller families. These often have remarkable life cycles.
They can be classified as either endoparasitic or ectoparasitic according to where they lay their eggs. Endoparasitic wasps insert their eggs inside their host, usually as koinobionts, allowing the host to continue to grow (thus providing more food to the wasp larvae), moult, and evade predators. Ectoparasitic wasps deposit theirs outside the host's body, usually as idiobionts, immediately paralysing the host to prevent it from escaping or throwing off the parasite. They often carry the host to a nest where it will remain undisturbed for the wasp larva to feed on. Most species of wasps attack the eggs or larvae of their host, but some attack adults. Oviposition depends on finding the host and on evading host defenses; the ovipositor is a tube-like organ used to inject eggs into hosts, sometimes much longer than the wasp's body. Hosts such as ants often behave as if aware of the wasps' presence, making violent movements to prevent oviposition. Wasps may wait for the host to stop moving, and then attack suddenly.