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Leaf-cutter ants pick up the pace when they sense rain

If their cargo gets wet, they will drop it and lose the day’s treasure

By
7:00am, June 15, 2018
leaf-cutter ants

STAY DRY  When the rain starts falling in Central America’s tropical forests, leaf-cutter ants (Atta cephalotes) hurry back to their nests — with or without their leafy cargo, which gets heftier when wet. 

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In Central America’s rain-drenched forests, leaf-cutting ants collect pieces of leaves on which they grow fungi for food. But the rain can hit hard, especially for a small ant. When leaf-cutting ants sense an incoming shower, they hoof it back to their nests, says a study in the May Insectes Sociaux.

Researchers from Argentina, Mexico and Peru tested how one species of leaf-cutting ants, Atta cephalotes, in Costa Rica deals with rain. The scientists placed hollow boxes filled with wet cotton on ant trails in the forest. When A. cephalotes walked through the boxes, they experienced higher relative humidity, as if it were about to rain. In another experiment, the researchers poured water on plants beside the trail to simulate falling raindrops. Both situations caused the ants to scramble to their nest up to 30 percent faster than normal, from about 1.21 meters per minute to 1.49.

The researchers think that leaf-cutter ants speed up to keep their cargo and themselves dry, with good reason: A wet leaf fragment weighs more than double a dry one. In the study, when the ants or leaves got wet, the insects readily dropped their harvest and returned to the nest. But by hurrying along at the first hints of rain, the ants could stay dry and hold onto the leaves.

Citations

A.G. Farji-Brener et al. Working in the rain? Why leaf-cutting ants stop foraging when it’s raining. Insectes Sociaux. Vol. 65, May, 2018. doi: 10.1007/s00040-018-0605-z.

Further Reading

L. Hamers. Ants were among the world’s first farmers. Science News. Vol. 192, November 11, 2017, p. 4

S. Milius. Classic view of leaf-cutter ants overlooked in nitrogen-fixing partner. Science News. Vol. 176, December 19, 2009, p. 8.

S. Milius. Old MacDonald was an ant. Science News. Vol. 154, November 21, 1998, p. 334.

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