Wasp

• 1. Introduction

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  Wasps are among the most misunderstood insects on the planet. Ask most people what comes to mind, and a 2018 study found the answers were nearly always the same three words: "sting", "annoying", and "dangerous". Yet the roughly 100,000 species of ichneumonoid wasps alone outnumber all vertebrate animals combined. They have spread to every continent except the polar regions, appear in the fossil record as far back as the Jurassic, and include both the world's largest social insect and the world's smallest known flying animal. What explains the gap between their fearsome reputation and their ecological indispensability? And why has a group this vast remained so little studied compared to bees?

• 2. Extremes of Size

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  Dicopomorpha echmepterygis, a solitary parasitoid in the family Mymaridae, measures just 139 micrometres in body length. That makes it the smallest known insect on Earth. A close relative, Kikiki huna, holds a separate record at 158 micrometres: the smallest known flying insect. Both fit comfortably on a pinhead.

  At the opposite end of the scale, the Asian giant hornet reaches several centimetres in length and is the only organism whose nests are regularly attacked by the honey buzzard. That bird is the sole known predator willing to raid the hornet's colony for larvae. Among solitary species, the giant scoliid Megascolia procer spans a wingspan of 11.5 centimetres and has subspecies in both Sumatra and Java. It targets a single host: the Atlas beetle Chalcosoma atlas. Tarantula hawk wasps reach a similar size and can overpower a spider many times their own weight, dragging it back to a burrow for their young. The female giant ichneumon wasp Megarhyssa macrurus carries an ovipositor so long and slender it bores through solid wood to deposit eggs on concealed horntail larvae buried inside.

• 3. The Parasitoid Majority

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  Most people picture wasps as nest-builders. The reality is that the vast majority of wasp species are solitary, and most of those are parasitoids: insects that lay their eggs on or inside a living host, which the larvae then consume from within. Unlike a true parasite, the wasp larva eventually kills its host. This one trait has driven explosive diversification.

  In a single study in Peru, 18 distinct wasp species were found living as parasitoids on just 14 fly species, all confined to two species of Gurania climbing squash. That density of specialisation is the rule, not the exception. The Ichneumonidae alone are thought to comprise around 100,000 species globally. Their extremely long ovipositors detect hosts by smell and vibration through wood, allowing them to reach Lepidoptera larvae buried deep in plant tissue. Some species take the strategy further still: the eggs of Euceros are laid beside caterpillar larvae, and the wasp larvae feed on the caterpillar's blood fluid. If a parasitoid later emerges from that same caterpillar, the Euceros larvae switch hosts and complete their development inside the parasitoid. One family, the Eucharitidae, has gone further still, specialising exclusively as parasitoids of ants, a feat almost no other parasite has managed given ants' formidable colony defences.

  Commercial horticulture has turned this parasitoid habit into a tool. Encarsia formosa, a parasitoid of whitefly, entered commercial use in Europe in the 1920s. Chemical pesticides pushed it aside in the 1940s, but interest revived from the 1970s onward. Today Encarsia is tested in greenhouses against whitefly on tomato, cucumber, aubergine, marigold, and strawberry. Aphidius matricariae is deployed against the peach-potato aphid.

• 4. Social Life and Its Origins

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  Of dozens of wasp families, only Vespidae contains truly social species. Within that family, the subfamilies Vespinae and Polistinae organise colonies around a single egg-laying queen and non-reproducing workers. The biological reason traces to a quirk of genetics shared across all Hymenoptera: sex is determined by a haplodiploid system, in which females carry two sets of chromosomes while males develop from unfertilised eggs with only one set. This makes sisters more closely related to one another than to their own offspring. Kin selection therefore favours helping a sister reproduce over reproducing independently.

  Wasps control offspring sex deliberately. A female stores sperm inside her body after mating and releases it selectively for each egg she lays. Withholding sperm produces a male; fertilising produces a female. The bacterium Wolbachia disrupts this control: experimental infection of Muscidifurax uniraptor induced thelytokous reproduction, eliminating the ability to produce viable male offspring. Nest construction is exclusively plant-based: workers gather wood fibres from weathered timber, chew them into a pulp mixed with saliva, and shape the material into combs arranged in a honeycombed pattern, often enclosed by a protective envelope. Placement varies by species. Dolichovespula media and D. sylvestris prefer trees and shrubs; Protopolybia exigua attaches nests to the underside of leaves; Polistes erythrocephalus builds near water. In temperate climates, Polistes erythrocephalus runs a reproductive cycle up to three months longer than the same species in warmer latitudes.

• 5. Ecological Roles Beyond the Sting

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  Pollen wasps in the subfamily Masarinae carry nectar and pollen inside a crop in their bodies rather than on external hairs. They pollinate plants in the genus Penstemon and across the water leaf family Hydrophyllaceae. Fig wasps in the family Agaonidae go further: nearly 1,000 species of tropical fig tree each depend on a specific fig wasp for pollination, with the relationship fully mutualistic. The wasps are equally dependent on their fig trees. In the Lower Cretaceous rocks of the Crato Formation in Brazil, fig wasps with modern anatomical features appear some 65 million years before the first fig trees in the fossil record.

  Kleptoparasitism runs alongside predation and pollination as a third ecological strategy. Cuckoo wasps, notably the Chrysididae, lay eggs in the nests of other wasps and exploit the provisions already stored there. Sand wasps in the genus Ammophila sometimes steal prey from nests of their own species, or remove a rival's egg and replace it with their own. The paper wasp Polistes sulcifer lays its eggs specifically in the nests of Polistes dominula, whose workers then feed the intruder's larvae directly. Emery's rule describes the general pattern: social parasites tend to target their closest relatives rather than distant ones. Dolichovespula adulterina, for instance, parasitises D. norwegica and D. arenaria within the same genus.

• 6. Wasps in Human Culture

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  Aristophanes staged his comedy Sphēkes, known in English as The Wasps, in 422 BC. The chorus is made up of old jurors who compare themselves to the insects, complete with stings. It is among the earliest known literary treatments of any animal.

  In the nineteenth century, Charles Darwin found wasps philosophically troubling. In an 1860 letter to the American naturalist Asa Gray, Darwin cited the Ichneumonidae specifically as evidence against a benevolent and omnipotent creator. The image of larvae consuming a living host from inside undermined, for Darwin, any comfortable theology of nature. H. G. Wells gave wasps a different kind of prominence in his 1904 novel The Food of the Gods and How It Came to Earth, in which giant wasps carry stings three inches long. Eric Frank Russell's 1957 science fiction novel Wasp is generally considered his best work. In Stieg Larsson's The Girl Who Played with Fire (2006), the character Lisbeth Salander uses "The Wasp" as her hacker handle and carries a wasp tattoo on her neck. Nine Royal Navy ships have borne the name HMS Wasp, the first an 8-gun sloop launched in 1749. Eleven United States Navy vessels have carried the same name, starting with a merchant schooner acquired by the Continental Navy in 1775. One of these, an aircraft carrier, earned two Second World War battle stars, prompting Winston Churchill to quip "Who said a Wasp couldn't sting twice?" The Westland Wasp, a military helicopter developed in England in 1958, served the Royal Navy and several other navies. Wasps RFC, the English professional rugby union club, took its name in 1867 at a time when insect names were fashionable for sports teams, and wore a first kit of black with yellow stripes.