The Namib Desert beetle runs as fast as possible to cool itself down in the blistering heat. Reported in the Journal of Experimental Biology, this is the first non-flying animal known to use exercise to cool off.
In their relentless search for food and mates, male Namib Desert beetles (Onymacris plana) spend their days travelling across the dunes of the Namib Desert on the south-western coast of Africa, occasionally taking breaks in rare patches of shade.
When moving over the 50ºC sand, these tiny, flightless beetles sprint at speeds of 1 metre per second using long legs that lift their disk-shaped bodies about 15mm above the ground, where the air is 10-15ºC cooler thanks to wind from the Atlantic.
With a lethal body temperature of 51ºC, male Namib Desert beetles have had to find ways to reduce how much heat they gain whilst out in the sun. And yet, counterintuitively, previous research has shown that running Namib Desert beetles have the same body temperature as those resting in the shade.
“We thought, well, actually, maybe it’s more than that. Perhaps it’s that they actually can cool down by running,” says Carole Roberts from the Gobabeb Namib Research Institute who took part in the study.
To investigate further, the researchers inserted miniature temperature sensors into the upper body of living and dead beetles.
Taking an initial measurement from all individuals, the team then released the live beetles back onto the dunes and simultaneously placed the dead beetles 15mm above the sand in the sun.
They then compared the live beetles’ body temperature 30 seconds into a sprint with that of the stationary beetles.
Despite having been exercising under intense solar radiation, the sprinting beetles were, on average, 1.5 ºC cooler than the dead beetles.
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How running helps beetles cool down
The team suspected that convection was behind this cooling effect, with the heat from their bodies transferring to the colder surrounding air. To confirm this, they conducted a lab experiment that mimicked the effect of males running under a range of solar radiation and wind conditions.
In these simulated environments, running at 1 metre per second in high solar radiation and no wind lowered the beetle’s temperature by approximately 13ºC.
“Because of the rate of increase [in body temperature], if they didn’t run in the sun, it would kill them in a few minutes,” says Duncan Mitchell from the University of the Witwatersrand who also took part in the study.
"There's this really unique strategy that's come to light,” says Meredith Johnson from North Dakota State University. “It kind of defies conventional understanding that exercise adds heat to the body.”
The team think Namib Desert beetles are not alone in using convection to cool off. "We’re really encouraging somebody else to go out and look for other animals who cool by running,” says Mitchell.
Find out more about the study: Beetling the heat – the diurnal Namib Desert beetle Onymacris plana cools by running
Top image: Namib Desert. Credit: Joh Henschel
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