The weird world of wasps and why we should worry if they are on the wane

We think of them as pests to run away from, or to squash with the nearest object to hand, before they sting us or target our jam sandwiches. But wasps are actually one of the most fascinating species around; apex predators that kill and dismember prey for their young and have complex and fascinating social lives.

This year they are in the spotlight after experts began to notice they were not around in the usual numbers. Unlike butterflies and bees, there is no nationwide effort to chart wasp numbers; they are very much neglected in the public eye.

That is despite the fact that there are more than 100,000 species of described wasps, with 9,000 of these in the UK, and scientists estimate five to 10 times this number are yet to be discovered. Most do not sting, and the large majority of those that do are solitary wasps that only hunt specific types of prey. The yellowjackets and hornets that do sting humans represent only about 70 species globally, and in the UK there are only nine species of these.

Dr Seirian Sumner is an entomologist at University College London who has spent her career studying wasps. She said she was “thrilled” that people were worrying about low wasp numbers because “usually they only get airtime when they start annoying people”.

“The fact that the low wasp numbers are making people take notice and, dare I say it, worry whether the lack of wasps is a bad thing, is really heartwarming for someone like me who’s been a cheerleader for wasps against a tide of wasp-fearmongering and negativity.”

However, she is unsurprised by this year’s low numbers: “The science tells us that cold, wet springs mean that foundresses – the big queen wasps that start appearing in spring – struggle to successfully grow a nest. This is because they are solitary at this time in the colony cycle and so need to do all the nest building, egg laying, prey hunting all by themselves. Rain and cold make this difficult; and of course their prey will have been affected by the poor weather too, compounding the challenge. So with fewer successfully founded nests in spring there will be fewer mature nests now. And predictably, fewer wasps bothering people.

“This is bad news. Wasps perform many important roles in the environment, as natural pest controllers, as pollinators and also in the case of the yellowjacket they are important decomposers – that’s why they happily scavenge the carrion at your BBQ,” said Sumner.

In the long term, wasp numbers were thought to be declining overall because of human activity, she said. “They will be affected in the same way as other insects by chemicals like pesticides – after all, these chemicals are designed to screw up insect physiology and neurology.”

The types of wasp that have captivated many scientists tend to be the parasitoid species. These fascinating creatures are under-studied and include the smallest insect in the world, the fairy wasp Dicopomorpha echmepterygis, which is wingless and blind and measures about 0.127mm in length. They are usually out of our sight and are beneficial as they control other insects such as caterpillars by feeding on them.

Social wasps are the ones we are most likely to come into contact with, particularly when they are older and seeking sugar – hence the jam sandwich attraction; they make nests and are separated into workers and queens, much like bees. Then there are solitary wasps that are laser-focused on their specific prey, anything from honeybees to spiders. These wasps are, like parasitoid wasps, unlikely to come into contact with humans unless they accidentally get lost and make their way into our homes. And all of them are members, along with ants and bees, of the Triassic-originating insect order Hymenoptera, the “membrane-winged” insects.

At the Natural History Museum, Dr Gavin Broad is charged with maintaining the institution’s wasp collection and is, predictably, besotted with them: “Wasps are apex predators, keeping pest insects at bay and generally being rather badass. Watching a wasp battling and dismembering a big dragonfly is awe-inspiring. They go to great lengths to feed their young on fresh protein and it’s only the adults, especially at the end of the nest season, which require sugar, which is when they come into conflict with people.”

Humans have learned a lot from wasps: “Watching social wasps build their paper nests is to get a glimpse of how people might have had the original idea for making paper from wood pulp. These nests are architectural wonders; I’ve enjoyed watching wasps painstakingly building their nests one strip of papier-mache at a time, and watching and listening to them chewing wood to make their pulp.”

He added: “They are a wonderful group to study as there is an awful lot still to be learned about their ecology. Even in Britain you can find undescribed species. I’m describing a new species of nocturnal parasitoid wasp which turned up in my garden light trap. The sheer efficiency of many parasitoid wasps is wonderful – and gory. Very frequently, a caterpillar turns out to be parasitized and you can watch the host disappear as it is completely consumed by wasp larvae.”

Prof Charles Godfray teaches evolutionary biology at Oxford University and has studied parasitic wasps for decades. “The larvae of parasitic wasp develop in the bodies of other insects and we think that they are really important. To explain it, if you look out of the window and think about why the Earth is so green when there are so many things that eat leaves, it is because caterpillars are controlled by parasitic wasps. They are extremely abundant and have an enormous effect when deciding the structure of ecosystems as we know it.”

Parasitic wasps were so important in their role as pest controllers, said Godfray, they were bred and released by scientists in areas where invasive pest bugs were accidentally introduced and threatened food supply.

But wasps also existed for their own sake and deserved to be there as part of the ecosystem, he added, as he cautioned against only viewing them in terms of their benefit to humans: “I guess I wouldn’t think about it in those terms – whether they are good or bad, they are just part of our natural community.”

As an evolutionary biologist, he is interested in how social wasps – the type that make nests and swarm around – evolved: “What is really weird about wasps, is there are thousands of species of them but only a small fraction of them have become social. They have evolved the very strange system of sociality where you have the queen and where you have workers. Darwin spent a lot of time studying it; it was of great puzzlement to Darwin. From an evolutionary point of view wasps along with ants and bees are absolutely fascinating.”

While wasp enthusiasts were once only found out in the field or leafing through libraries, social media had helped to connect them, Godfray said. “There are just too few people interested in these insects. Interestingly there are now at least two Facebook groups of people who are interested in parasitic wasps who exchange photographs and discuss issues about identifying them. One of the positive things about the internet is that there are now so many resources. Now very keen citizen scientists can make important contributions.”