Dung beetles show their love by sharing the load

Newswise — Dung beetles share the load when it comes to showing their affection for each-other, when transporting a “brood ball”.

Dung Beetles are known for collecting piles of dung for various uses. One of these is called a “brood ball”, where they lay an egg in each ball, after they have buried it. When the egg hatches, the larva uses the ball as a nursery, eating the ball from the inside out, shaving off layers to keep the ball intact.

“The brood ball is a vehicle that the adult beetles use to get their genes into the next generation,” says Professor Marcus Byrne of the School of Animal, Plant and Environmental Studies at the University of the Witwatersrand (Wits University), in Johannesburg, South Africa. 

Byrne and Professor Marie Dacke of the Vision Group at Lund University, Sweden, have studied the navigational behaviour of dung beetles for over two decades. They have found that dung beetles’ source of food is never at the same location, and consequently they have an extremely limited way of memorising environmental cues around the dung. Instead they make use of the stars, wind and the sun and moon, among others, to find their way away from dung sources to avoid competition.

Ball-rolling dung beetles transport balls of dung and bury them in the soil, for feeding or breeding. After carefully constructing a dung ball at the dropping site, these beetles immediately roll it away along a linear path avoiding intra- and interspecific competition for food and nesting sites. 

In their latest study, published in The Proceedings of the Royal Society, Byrne, Dacke and  lead author Dr Claudia Tocco (formerly at Wits and now at Lund University, Sweden)  found that when transporting a brood ball, male and female dung beetles work together transporting the ball to a location that neither of them know about beforehand.

“It is important to note that each individual ant or spider involved in the cooperative transport of food strives towards the same final known destination; either a nest or a tightly spun shelter, in which to store the food,” says Tocco. “In contrast, pairs of male and female dung beetles fluently collaborate to transport food to a location unknown to either party at the start of their common journey.”

For their study, Byrne and colleagues studied the transport behaviour of brood balls by pairs of the Southern African Sisyphus fasciculatus and European Sisyphus schaefferi. Both these species of dung beetles are small in size and associated with woodland habitats, where they commonly encounter obstacles on their rolling paths, usually plant material that falls from the trees.

The team found that pairs of Sisyphus beetles cooperate in the transportation of brood balls, resulting in greater transport efficiency in the face of obstacles. This cooperation is driven by coordinated movements where the male steers while the female primarily assists in lifting the ball whenever obstacles need to be climbed.

The characteristic straight-line escape not only guarantees that the ball-rolling beetles will not inadvertently return to the competition at the dropping site, but also effectively maximizes the beetles’ distance from it with every step taken.

When paired up for mating, the exact location at which the pair chooses to stop and bury their brood ball is also selected on the go, on the basis of the properties of the terrain being traversed.

“To ensure smooth and effective transport, efficient communication must be taking place between the male and female of the beetle pair. However, the mechanism that allows the beetle pair to communicate and coordinate their joint actions is currently not known,” says Byrne. This opens up opportunities to investigate collaboration in many other fields, such as robotics.