We have learned to detest wasps because we’ve been taught to do so by our families, educators, media, literature and entertainment. It’s not our fault – we are products of our local cultures. Science must shoulder its share of responsibility for this. Over the last 30 years, there have been three times more scientific papers published on bees than on wasps, and conference talks on bees outnumber those on wasps four to one. The bee-bias in research has become more extreme over recent years, fuelled by large investments by governments into pollinator research, driven by our own self-servicing interests. In a world without pollinators, we go hungry.

But funding streams cannot shoulder the blame entirely for science’s neglect of wasps. Some of our greatest minds have subtly sowed the seeds to promote scientific distance from them. It was parasitic Ichneumonid wasps that caused Charles Darwin to question the omnipotence of God and the story of Creation. In a letter to the botanist Asa Gray in 1860, Darwin wrote: ‘I cannot persuade myself that a beneficent and omnipotent God would have designedly created the Ichneumonidae with the express intention of their feeding within the living bodies of caterpillars.’

Even contemporary wasp scientists concede the social stigma carried by wasps. American scientist Mary Jane West-Eberhard has devoted her life to studying wasps, but admits ‘they terrorize housewives, ruin picnics, and build large aerial nests that challenge fleet-footed stone-throwing boys the world over.’ William D. Hamilton, a scientist who has had the most profound influence on our understanding of social evolution, acknowledged that ‘Social wasps are amongst the least loved insects.’ And Phil Lester, a New Zealand scientist who has been working hard to control invasive wasps (kindly introduced by the British) in his homeland, embraced the hype of public revulsion to wasps and called his book on them The Vulgar Wasp.

When scientific champions of wasps are struggling to describe these insects as anything but the gangsters of the insect world, what hope do wasps have? What happens in a world without wasps? We don’t know for sure because we lack the basic science to tell us precisely what they do. But we know that wasps must be important for functioning ecosystems and a healthy planet. We know that they prey on the insects that would otherwise be a nuisance to us. In a world without wasps we would almost certainly need to use a lot of chemicals to keep other pests at bay. Th is, at least, is a good argument to forgive wasps for their sting just as we forgive bees.

It’s time to solve the enigma of these beautiful, diverse and mysterious creatures. Let’s give them a chance to prove themselves as worthy of our attention.

II

‘From so simple a beginning endless forms most beautiful and most wonderful have been, and are being, evolved.’ I like to imagine that Darwin was admiring the beauty and wonder of wasps in his garden when he wrote these closing lines to his magnum opus On the Origin of Species by Means of Natural Selection, the book that revolutionised our understanding of life on earth. Many groups of organisms could be described as ‘endless’ in form, but natural selection has had an especially delicious time with wasps – teasing, testing, modelling and remodelling their forms and functions, spawning mind-blowing diversity. But this book is not a wasp encyclopedia; I simply cannot include them all. In fact, no one could, because for every wasp that has been named, there are likely to be around ten other species that we’ve not yet discovered.

I have to admit that Darwin was more likely thinking of beetles when he was writing his closing remarks for On the Origin of Species. Beetles are remarkable in their diversity: truly one of nature’s wonders. Indeed, the second most famous quote of another evolutionary biologist, J.B.S. Haldane, is that any intelligent creator of life must have had ‘an inordinate fondness for beetles’. His observation was pertinent at the time he said it (the 1950s) as the debate between evolution and religion was tipping in favour of evolution.

If God really did create all beings on earth, He must have had a special penchant for beetles: they are the most numerous in terms of described species of any animal group, with 387,000 species. Accounting for cryptic species (those that look very similar to other species) and those yet to be discovered, scientists think that there could be around 1.5 million species of beetles. They are also among the most striking insects in appearance, from the flamboyant and exquisite to the ridiculous. In the absence of an intelligent creator, the diversity of beetles could have evolved through natural selection to attract members of the opposite sex, to repel salivating predators or to act as camouflage.

Because beetles look so extraordinary, we almost certainly suffer from a form of beetle-bias, making us more likely to find and describe new species of beetles than any other insect. People have noticed, collected and catalogued them for hundreds of years. In the nineteenth century, any respectable naturalist would have proudly shown off their personal collection of beetles and excitedly competed with friends for the largest, brightest or most outlandish specimens. In our admiration of beetles, we have inadvertently skewed our knowledge of insects in their favour.

Wasps belong to the order Hymenoptera, which includes bees and ants as well. Th ere are around 150,000 described species of Hymenoptera. Of these, wasps make up over 80 per cent, with around 80,000–100,000 named species, almost five times more than there are bee species, and over 7 times more species than ants (which number about 13,000). Yet we notice and report wasps a lot less. In many parts of the world, wasp sightings are dominated by those of our friend the yellow-and-black-striped picnic wasp – the yellowjacket – that invades our personal space.

Of course, the number of species described does not reflect how many there actually are. Over a million insect species have been described, for example, but scientists estimate that there are likely to be 5.5 million species of insects on the planet. One of the big problems in counting species is geographical bias: the most intensively sampled parts of the world (for example, North America and Europe) are among the least biodiverse. Every insect order is likely to be several times more species-rich than current numbers suggest, and the Hymenoptera[*] especially so, with 60–88 per cent of its species thought to remain undescribed. Even the most conservative estimates suggest that there are between 600,000 and 2.5 million species of Hymenoptera. In areas that have been well sampled, such as temperate regions and some specific tropical ecosystems, hymenopteran species already outnumber beetles.

The vast majority of hymenopterans are hidden among the tiny and obscure parasitoid wasps. Parasitoids are insects that lay their eggs in (endoparasitoids) or on (ectoparasitoids) other organisms. When the egg hatches into a hungry larva, it proceeds to eat the living host alive as it grows. Parasitoids should not be confused with parasites, which spend their whole life living in or on a host, rather than just the larval stage. Some parasitoid wasps sport special severing structures on their heads which they use to tear their hosts open when they’re ready to leave home. Eating living prey from the inside out may sound terrifying, but these wasps don’t have the much-feared stings paraded by other wasps. In their place, parasitoids have an egg-laying tube called an ovipositor. Ovipositors are terribly useful: they reach places that other body parts could only dream of reaching. They can be inserted through tiny crevices into tree trunks, undergrowth or soil to deposit a precious egg, along with a cocktail of venom and cooperative viruses, into an oblivious caterpillar or beetle larva.

Wasps are not the only insect parasitoids, but they are by far the most diverse, numerous and species-rich. They are also incredibly important, as they perform a critical role in ecosystems by regulating populations of other insects. It is no surprise that they have been used extensively by humans in biocontrol. In some parts of the world these insects are farmed on a factory scale to be released into fi elds of maize and sugar cane, where they seek out caterpillars and other pests to lay their eggs in.

There are at least 80,000 described species of parasitoids. Most are diminutive in size: the tiniest are the fairyflies (Mymaridae – which are of course wasps, not flies), which can be as tiny as 0.14 millimetres, making them the world’s smallest insects. Others, like the Ichneumonid wasps, can be several centimetres long, or twice that size if you take their ovipositor into account. Body size matters in species discovery. Take the 4,200 species of beetles found in the UK (arguably the best-studied group of beetles in the world): the mean body size of newly described British beetles decreased significantly between 1750 (when records began) and 1850 because entomologists had been much more likely to spot, collect and describe larger-bodied species before they noticed the smaller-bodied ones.

Given how tiny most parasitoid wasps are, discovery of their species starts at a disadvantage. To make matters more complicated, there are parasitoid wasps that lay their eggs on other parasitoid wasp larvae! These hyperparasitoids (parasitoids that live off other parasitoids) are often even smaller than their hosts – they are ‘micro-wasps’. They represent a fourth layer of the food web: the hyperparasitoid wasp lives off the parasitoid wasp that lives off the caterpillar which lives off the host plant. Such multi-layered trophic chains can be unimaginably complex and are exhaustingly intricate examples of the endless forms of wasps and the plants and animals their lives are entwined with.

Finding parasitoids is just the first step; identifying them is exceedingly tricky too. Until recently only a handful of scientists around the world could do this as it required specialist knowledge of specific taxonomic traits, limiting the rate at which new species could be described even if they’d been discovered. But whenever scientists have taken a closer look at these creatures, they find many new species. This is especially so now with the use of DNA markers, which has made distinguishing similar-looking species less of a specialist skill and has exposed cryptic species that previous techniques had failed to identify. As a result, the number of named species of parasitoid wasps has exploded. It seems possible that wasps may in fact be the most species-rich of all insects, catapulting Haldane’s fondness for beetles into a dusty corner of twentieth-century biodiversity science. We need only to visit a small area of a Central American rainforest and a 34-year-long study of caterpillars to understand why.

Área de Conservación de Guanacaste is a national park in north-western Costa Rica. It is around 1,200 square kilometres – a little smaller than Greater London – and is a protected area with diverse habitats and rich biodiversity. Over the last 34 years, scientists have reared thousands of caterpillars collected from this reserve, and from these caterpillars emerged many thousands of parasitoid wasps, most of which were undescribed. Th e researchers have their work cut out, sorting through all these wasps; but they’ve made a start by focusing on a single genus of a braconid micro-wasp, Apanteles, which are of economic interest because they have been used widely in biological control of caterpillar crop pests. In this part of Mesoamerica, only 19 species of Apanteles wasps had previously been described. From among 4,100 individual wasps, the scientists named no fewer than 186 new species: that’s almost ten times more species of this genus than were previously known for this region. Remember, this is a single genus of wasps from a very small corner of the world.

Are we underestimating the number of species of parasitoid wasps by a factor of ten? If so, we’d be looking at there being in excess of 800,000 species of parasitoid wasps across the world. Of course, this may be an overestimate, as Área de Conservación de Guanacaste is known to be highly biodiverse. As an example, the region has five times more beetle species than are found in the whole of the UK. Th e UK is one of the least biodiverse nations on the planet, but even assuming that the species richness of this small area of Costa Rica is five times that of any other area in the world, this would still bring the predicted global number of species of parasitoid wasps to 160,000 – that’s more than all the described hymenopterans put together.

If you aren’t convinced by this, a foray into the ecology of parasitoids might persuade you. Beetles are up there with caterpillars as being the most favoured hosts for parasitoid wasp brood. Based on the known diversity of beetle hosts, and the fact that several different species of wasp can parasitise the same host beetle species (some parasitise larvae, others eggs), scientists have estimated that there are likely to be between two and three times more parasitoid wasp species than there are beetles. Before these studies, it was thought that parasitoids accounted for almost 80 per cent of described wasp species, but developments like these send diversity estimates for wasps into orbit.

If there is an intelligent creator of life on earth, almost certainly they had an inordinate fondness for parasitoid wasps.

[*] Reporting the number of described species is harder than you’d think. This is because sometimes different names are given to the same species. Accounting for synonyms, the minimum estimate of described Hymenoptera is 117,000; the maximum estimate is around 150,000.

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Ecology, Environment, Mind, Nature