There comes a time in a dung beetle’s life when the only hope of overcoming an obstacle without losing their prized ball is a partner who can pull off a decent headstand.
When their path is blocked, pairs of dung beetles carefully coordinate their actions, with males grabbing the dung ball from above, and females going into a headstand to push the ball off the ground with their legs, researchers say.
The unusual, cooperative behaviour between spider dung beetles is believed to be a unique example of animals other than humans working together to move objects around without knowing their final destination.
While ants coordinate to haul food to their nests, and social spiders cooperate to carry prey to their shelters, both know where they are heading and when they have arrived. With dung beetles, couples start rolling their dung balls with no idea where they will stop.
“It’s the first species that’s been recorded that can coordinate transport in this way,” said Dr Claudia Tocco, who studies animal behaviour at Lund University in Sweden. “They don’t know where they are going, but they can still coordinate to move the object together.”
Tocco investigated South African spider dung beetles in the hope of learning what pairing-up achieved. In other species of dung beetle that roll balls in pairs, females catch a ride by clinging to balls of dung, or walk behind their ball-rolling male.
She gave dung beetles access to cow dung and compared how well single beetles and mating pairs rolled the balls when obstacles of different heights blocked their path. The particular species live in forests and face constant obstructions in the shape of plants and rocks. They bury the balls for food or to lay eggs in.
The researcher found that male beetles always took the role of dung ball dragger, grabbing the ball with their front legs as they walked backwards. Females always helped from behind, walking backwards with their rear legs up on the ball.
On flat ground, pairs of beetles rolled no faster than single males, but faced with hurdles, the couples surged ahead. When challenged by walls up to 9cm tall, males started to climb and drag the ball up, as females worked themselves into a headstand and pushed with their legs to help the ball off the ground. The females then held on to the ball as the male pulled it up – lifting about 10 times his body weight.
At times, males clung to walls with only one claw and females repeatedly saved them from falls when they lost grip, the scientists wrote in Proceedings of the Royal Society B. Pairs of beetles were faster than single ones and more efficient over obstacles, which would be “extremely beneficial” in the forest, the authors noted.
But while pairing up makes sense, how the beetles coordinate their actions remains a mystery. “How does a beetle with a brain smaller than a grain of rice communicate? And how do they coordinate with each other in performing this task?” said Tocco. “They don’t know where they are going.”
