(but see text)
Aculeata is a subclade of Hymenoptera. The name is a reference to the defining feature of the group, which is the modification of the ovipositor into a stinger (thus, the group could be called "stinging wasps", though the group also contains the ants and the bees). In other words, the structure that was originally used to lay eggs is modified instead to deliver venom. Not all members of the group can sting; a great many cannot, either because the ovipositor is modified in a different manner (such as for laying eggs in crevices), or because it is lost altogether.
This group includes the bees and ants and all of the eusocial Hymenopterans. It is commonly believed that the possession of a venomous sting was one of the important features promoting the evolution of social behavior, as it confers a level of anti-predator defense rarely approached by other invertebrates.
The use of the name Aculeata has a long history at the rank of infraorder or division. The Aculeata are a good natural group, containing all the descendants of a single common ancestor. The Aculeata are therefore maintained as a taxon, either at infraorder or division rank or as an unranked clade.
Among the parasitic wasps, the Ichneumonoidea seem particularly closely related to the Aculeata. If taxonomic ranks are used, it may, therefore, be best[according to whom?] to treat the latter as a division and divide the Apocrita into some six infraorders representing lineages of about equal standing, one of which would unite the Aculeata and the Ichneumonoidea.
Having the same taxonomic rank does not imply equal evolutionary standing, whereas placement in the same higher-ranked taxon ideally does, or at least implies that regardless of what specific rank they have, the lower-ranked taxa are all part of the same evolutionary radiation. Therefore, were the Aculeata and the Ichneumonoidea to be placed in an infraorder, the former would still be considered a division and the latter a superfamily. Despite having different ranks, they would be members of the same taxon and sister lineages.
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