New research from a University of Hull scientist has revealed what may well be ‘the world’s laziest insect’ in a new study published in the Journal of Animal Ecology.
Dunatothrips aneurae, tiny insects less than 3mm long – really no more than walking hyphens – live in small groups in the remote Australian outback, feeding harmlessly on the surface of leaves. Their miniature nests are built on Acacia trees from a material a bit like silk. They are not bothered by predators and their biggest threat is drying out in the heat if their nest is damaged by wind.
Zoology lecturer Dr James Gilbert’s research saw him spend three years in Australia studying the social lives of these diminutive bugs. Dunatothrips are members of the thrips, known as ‘thunderbugs’ owing to a common myth that they come out during thunderstorms. While their cousins are pests of tomatoes, Dunatothrips bother nobody.
Dr Gilbert discovered that, if the silk nest is damaged, only one or two individuals usually step up to repair it. The remaining group members enjoy the benefits of the repaired nest, but don't ever seem to do their fair share of work.
Intrigued, Dr Gilbert set out to investigate what these ‘lazy’ thrips were doing. In other insects like bees, queens specialise in producing eggs while others act as workers – so were these individuals acting like queens? No: when he dissected ‘helpers’ and ‘non-helpers’, he found that it was the helpers that tended to be the ones carrying eggs. Non-helpers were very often not reproductive.
Maybe, like some bird societies, they took it in turns – so that the lazy ones help out when others are unable to? No: when first responders were removed, the lazy individuals remained just as unhelpful as before.
Or perhaps they were like paper wasps, where some group members conserve their energy, waiting for a chance to breed later? Dr Gilbert removed all nestmates except for the lazy individual, effectively gifting it a nest. They declined even this opportunity as well – producing few or no eggs and taking up to five times as long to repair the nest as a helpful thrips put in the same situation.
So what is the point of these animals? Dr Gilbert figured that these individuals must simply be of poor quality – unable to breed or build nests on their own. Faced with a bad situation like this, animals often make the best of a bad job. So these thrips freeload by joining a group where their few offspring can benefit from others’ effort.
“It’s still a mystery why their nestmates don’t kick them out,” said Dr Gilbert. “But it probably has to do with them being unusually chilled out in the face of any kind of provocation whatsoever, even dangerous intruders that threaten their nest.” Nestbuilding is risky work because you might fall out or be blown away. If you might die at any moment, it is a good idea to tolerate the presence of others who can carry on your nestbuilding work and help keep everyone’s babies alive. A simple evolutionary way to achieve this is to drop all aggression towards anyone at all, including intruders of different species – or even freeloaders like nonhelpers.
“So, while Dunatothrips may be the world’s least consequential insects, they are certainly not the least interesting. The evolution of these non-helpers is helping us understand how different kinds of societies evolve.”
This research focused on thrips is quite a contrast to some of Dr Gilbert’s other research projects which revolve around bees – some of the world’s most industrious insects. In recent years, Dr Gilbert has shown that growing mason bee young have to count their carbs in the pollen they are given by parents, but are relatively robust to some pesticides.
Read Dr Gilbert’s paper titled “Investigating the role of non-helpers in group-living thrips” here.