Why Don’t Ants Drown?…

From the Globe & Mail

THE QUESTION: “Why don’t ants drown in the passageways of their anthills during a heavy rainstorm or melting snow?” asked Bill Cunningham of Sackville, N.B.

THE ANSWER: “Two strategies allow ants to deal with potentially catastrophic water from rain or melting snow — surviving the water or avoiding the water,” writes Alex Smith, an assistant professor of molecular ecology at the Biodiversity Institute of Ontario at the University of Guelph.

Surviving the water: Individual ants can survive complete submersion for hours, he says. And some species that live in areas that are commonly flooded can survive underwater for days.

“They accomplish this by closing their spiracles (the openings in their body wall that lead to their respiratory surfaces or ‘lungs’) and reducing their oxygen consumption to as little as 5 to 20 per cent of their normal rate.” He says other species, including the invasive fire ant, form rafts out of their bodies that allow the queen and brood to survive the flooding and re-establish the colony following the retreat of flood waters.

Avoiding the water: “Many anthills have design features that reduce the soil moisture content within the mound compared with levels in the adjacent soil,” he writes.

“One advantage in an anthill is that the height of a mound allows the colony to move up to avoid rising flood waters, and some of these mounds can be over a metre tall.” Underground cavities can also be sealed off from the water, he says. “Some tropical ants in mangrove swamps … literally use their heads to block the tunnel opening during periods of flood.”

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