Taxonomy and phylogeny
The wasps are a cosmopolitan
paraphyletic grouping of hundreds of thousands of species,
 consisting of the narrow-waisted
Apocrita without the
 The Hymenoptera also contain the somewhat wasplike but unwaisted
Symphyta, the sawflies.
The term wasp is sometimes used more narrowly for the
Vespidae, which includes the
common wasp or
yellow jacket genera
Dolichovespula and the
hornets, Vespa; or simply for the common wasp and close lookalikes.
Hymenoptera in the form of Symphyta (
Xyelidae) first appeared in the fossil record in the
Lower Triassic. Apocrita, wasps in the broad sense, appeared in the
Jurassic, and had diversified into many of the extant superfamilies by the
Cretaceous; they appear to have evolved from the Symphyta.
 Fig wasps with modern anatomical features first appeared in the
Lower Cretaceous of the Crato Formation in Brazil, some 65 million years before the first fig trees.
The Vespidae include the extinct genus
Palaeovespa, seven species of which are known from the
Eocene rocks of the
Florissant fossil beds of
Colorado and from fossilised
Baltic amber in Europe.
 Also found in Baltic amber are crown wasps of the genus
Wasps are a diverse group, estimated at over a hundred thousand
described species around the world, and a great many more as yet undescribed.
[b] For example, there are over 800 species of
fig trees, mostly in the tropics, and almost all of these has its own specific
fig wasp (
Chalcidoidea) to effect pollination.
, a parasitoid. The body of a female is c. 2 inches (51 mm) long, with an ovipositor c. 4 inches (100 mm) long
Many wasp species are parasitoids; the females deposit eggs on or in a host
arthropod on which the larvae then feed. Some larvae start off as parasitoids, but convert at a later stage to consuming the plant tissues that their host is feeding on. In other species, the eggs are laid directly into plant tissues and form
galls, which protect the developing larvae from predators but not necessarily from other parasitic wasps. In some species, the larvae are predatory themselves; the wasp eggs are deposited in clusters of eggs laid by other insects, and these are then consumed by the developing wasp larvae.
The largest social wasp is the
Asian giant hornet, at up to 5 centimetres (2.0 in) 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
Megascolia procer, with a wingspan of 11.5 cm,
 has subspecies in
 it is a
parasitoid of the Atlas beetle
 The female giant ichneumon wasp
Megarhyssa macrurus is 12.5 centimetres (5 in) 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.
There are estimated to be 100,000 species of
ichneumonoid wasps in the families
Ichneumonidae. These are almost exclusively parasitoids, mostly utilising other insects as hosts. Another family, the
Pompilidae, is a specialist parasitoid of spiders.
 Some wasps are even parasitoids of parasitoids; the eggs of
Euceros are laid beside
lepidopteran larvae and the wasp larvae feed temporarily on their
haemolymph, but if a parasitoid emerges from the host, the
hyperparasites continue their life cycle inside the parasitoid.
 Parasitoids maintain their extreme diversity through narrow specialism. In Peru, 18 wasp species were found living on 14 fly species in only two species of
Gurania climbing squash.