Dung beetles in silicon boots reveal heat avoidance strategy

The ground temperature in the African savannah can reach 60°C in the middle of the day. The burning sand presents a problem for many of the animals that live there, especially for small insects that spend their lives on the surface of the sand. Some insects seek protection in the shade or climb up blades of grass to escape the worst of the heat.

However, the South African dung beetle has come up with its own strategy. It simply climbs on top of its rolled-up meal, a ball of dung. The dung ball functions as a kind of air conditioning unit. The fresh dung ball is made up of moist dung from a large mammal. When the moisture in the dung ball evaporates in the heat, the ball is cooled down.

“The dung beetles climb on top of their dung balls when their heads and front legs become overheated”, says Jochen Smolka, a researcher at the Department of Biology at Lund University, who has carried out the research with colleagues from Lund and other researchers from South Africa.

The dung beetle’s main interest in the dung ball is to eat it, but the beetle has also worked out how to cool down on top of the ball. The Lund researchers have been able to prove this by studying the dung beetles’ behaviour in different experiments. Dung beetles on hot sand were seven times more likely to climb up onto their ball than dung beetles that rolled their balls on cooler sand. In another experiment, the researchers put a type of silicon boot on the front legs of a number of dung beetles to protect their feet from the heat. The results showed that dung beetles with silicon boots did not climb up onto their balls as often.

“Our study shows that insects employ sophisticated methods to regulate their body temperature. Evolution has an incredible ability to utilise existing materials for new functions”, says Jochen Smolka.

Not all species of dung beetle roll their meals away in the form of dung balls; only around ten per cent demonstrate such behaviour. The reason they roll the balls away from the pile of dung is to be able to eat in peace, without competition from other beetles.

The study has been published in the journal Current Biology: http://www.cell.com/current-biology/fulltext/S0960-9822%2812%2901061-5

A clip of dung beetles rolling balls of dung and cooling themselves:

A clip taken with a heat camera showing dung beetles rolling balls of dung and cooling themselves:

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