Kill, Fido! Docile ants become aggressive guard dogs after a secret signal from their caterpillar overlord. The idea turns on its head the assumption that the two species exchange favours in an even-handed relationship.

The caterpillars of the Japanese oakblue butterfly (Narathura japonica) grow up wrapped inside leaves on oak trees. To protect themselves against predators like spiders and wasps, they attract ant bodyguards, Pristomyrmex punctatus, with an offering of sugar droplets.

The relationships was thought to be a fair exchange of services in which both parties benefit. But Masaru Hojo from Kobe University in Japan noticed something peculiar: the caterpillars were always attended by the same ant individuals.

“It also seemed that the ants never moved away or returned to their nests,” he says. They seemed to abandon searching for food, and were just standing around guarding the caterpillar.

Read more on New Scientist website.