Named for their membrane-like wings (hymen = membrane in Greek, while pteron = wing), hymenopterans include bees and wasps. Ants also belong to this order, but except for their reproductive forms, called alates, this family (Formicidae) has abandoned flight to create colonies that have been described as superorganisms of unmatched complexity.
Bees and hornets are probably the most familiar members of the group. Though feared by many people, these social insects are vital to the health of both ecosystems and human societies, as the former are tireless pollinators as well as efficient honey producers, while hornets prey on a large variety of other insects, including pest species.
Most hymenopterans, out of a total of more than 110,000 species, are solitary creatures with sometimes very strange and specialised lifestyles. Closely related to carpenter bees, blue-banded bees (Amegilla sp.) nest in ground burrows and are seldom at rest, except at night when they can be found sleeping with their mandibles firmly grasping a shoot or leaf.
Adult bees and wasps feed on sugar-rich plant-based food such as nectar or fruit, but the larvae of wasps are carnivores that require living flesh. Pompilids are large spider-hunting wasps that attack even tarantulas, which they bury alongside an egg that will hatch to feed on the paralysed victim. Even larger are the Scoliids, which use scarab beetles as hosts for their larvae. Another group of hunters, the Sphecids or digger wasps, seek out various prey from flies to cockroaches.
Other hymenopterans, such as so-called cuckoo bees from various families, jewel wasps (Chrysididae) and velvet ants (Mutillidae) are parasites that invade the hives of host bees or wasps to deposit their eggs in the food or larval cells. Parasitism, and hyperparasitism (in which a parasite is itself the victim of another parasite) is prevalent among solitary wasps, and it is likely no species of spider or insect, including many parasitic wasps themselves, is immune to attack from some species of wasp. Fairy wasps, which are possibly the smallest flying insects, at just half a millimetre long, lay their eggs in the eggs of other insects and thus are used to help control crop pests such as plant hoppers.
Perhaps the most bizarre development is the tight relationship between fig wasps (Agaonidae) and fig trees (Ficus spp.). Fig trees can only be pollinated by these tiny wasps, which are able to squeeze into the unfertilised fruit and convey pollen from tree to tree. In return, the wasps have a safe place to lay their eggs. The discovery of this symbiosis was crucial for commercial fig orchards, as people were earlier puzzled why fig trees would produce copious fruit that never ripened. In tropical rainforests, fig wasps are vital links in the ecosystem, as many birds and large mammals such as hornbills, sun bears and monkeys rely on figs for their survival.