Ants forage at 'safe' temperatures

Published: Wednesday 30 September 1992

The silver ant -- Cataglyphis bombycina -- is the undertaker of the Sahara desert -- a role it has been forced to adopt because of its own body limitations and because of a small lurking, desert lizard that loves to gobble them alive.

Rudiger Wehner of Zurich University began a study of these ants wanting to know how they cope with high heat and why they confine themselves to brief bursts of midday activity. He reports (Nature, vol 357 no. 6379) that silver ants confine themselves to their relatively cool burrows until the temperature at ant height (4 mm off the ground) reaches 45-47oC, by when all other arthropods invertebrate animals with external skeletons, including desert ants, have either found shelter or perished.

Scout ants emerge from burrows early in the morning and monitor the rising temperature. When the temperature is just right, they trigger a dramatic burst of activity, in which a few hundred ants pour into the open and scurry about for three or four minutes. They forage feverishly, gathering corpses of woodlice, spiders and insects that have succumbed to the heat and then scoot back to their burrows before the temperature at ant height reaches 55C.

Silver ants can cope with higher body temperatures than have been recorded for any other land -- dwelling species, but as the temperature rises, the ants spend more and more time cooling off atop stems of dried vegetation. If the ants fail to find these stems, their body temperature rises to 55C -- their lethal limit -- and they die. The ants, however, face yet another danger that forces them to forage close to their burrows. The danger in from a small desert lizard that loves to feed on silver ants and so burrows close to silver ant colonies. However, the heat forces the lizard to retreat underground -- just about the time that the ants are about to emerge, aware instinctively that had they emerged earlier they would have been snatched up by an ant-hungry lizard.

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