Wasps provide support to their extended families by babysitting at neighbouring nests, researchers have found.
The study, by biologists at the universities of Bristol, Exeter and University College London, suggests that animals should seek to help more distant relatives if their closest kin are less in need.
Researchers closely observed 20,000 baby wasps and their carers on colonies around the Panama Canal.
Their work – published in the journal Nature Ecology and Evolution – found worker wasps became less useful as the number of colony members rose, due to a surplus of help.
Dr Patrick Kennedy, of the University of Bristol, said the worker wasps then went to babysit the larvae of relatives at neighbouring nests.
“The fact that these paper wasps in Central and South America help at other colonies is really bizarre when you consider that most wasps, ants and bees are extremely hostile to outsiders,” Dr Kennedy said.
“To solve this puzzling behaviour, we combined mathematical modelling with our detailed field observations.
“We ended up being stung a lot. But it was worth it, because our results show that worker wasps can become redundant at home.
“A wasp on a colony with few larvae but lots of other workers becomes almost useless – the best thing to do is to babysit the larvae of other relatives.”
Since Darwin, biologists have been trying to understand how altruism evolves in animals.
In 1964, biologist WD Hamilton found that animals lavished help on their families because they shared many genes.
This meant copies of an individual’s genes would then triumph in the population.
However, Hamilton was surprised to note that Polistes wasps in Brazil were leaving their close family on their home nests and flying off to help neighbours, who were less closely related.
Professor Andy Radford, from the University of Bristol, said: “By helping more distant relatives who are more in need – those living next door with fewer carers – workers can pass on more copies of their genes overall.
“We believe that similar principles of diminishing returns might explain seemingly paradoxical acts of altruism in many other social animals.”
Professor Seirian Sumner, of University College London, previously found that more than half the workers in a Panamanian population were helping on multiple nests.
Wasps usually viciously attack outsiders and so their behaviour offers “amazing windows into the evolution of selflessness”, Prof Sumner said.
“There is so much going on in a wasp nest – power struggles, self-sacrifice, groups battling against the odds to survive,” Prof Sumner added.
“If we want to understand how societies evolve, we should look more deeply at wasps.”
The fieldwork was supported by the National Geographic Society and the Smithsonian Tropical Research Institute in Panama.