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How termites ‘hear‘ about trouble

The insects use their legs to detect danger signals

By
8:30am, August 15, 2014

Headbangers, to the nest! Soldier termites use their heads to sound an alarm when a predator nears. And their legs do the “listening.”

Christoph Bosch

When it comes to sensing danger, termites use their heads — and legs. The insects can tell which direction to run using a precise biological timer, scientists report in a new study.

A common African termite builds mounds that stand a meter (a little over three feet) or more tall. Known as Macrotermes natalensis, these insects also inhabit underground tunnels that stretch over an area as big as a large home. And when a predator comes knocking — like a termite-eating aardvark — the insects sound a natural alarm system.

To sound a warning, soldier termites smack their heads against the floors of their tunnels. This head banging sends vibrations down the tunnels at about 130 meters (430 feet) per second. As other termites pick up the signal, they’ll bang their heads, too, relaying the warning. In the wild, this would signal worker termites to go deep into the nest for protection as soldiers head for the source, to do battle.

In the new study, Felix Hager and Wolfgang Kirchner figured out how those soldiers use those signals to know which direction to run. Both men are biologists at Ruhr University Bochum in Germany. They published their new findings July 15 in the Journal of Experimental Biology.

Termites sense the warning vibrations with all six of their legs. They sense it first in the leg nearest the source of the drumbeat. They feel it last in the leg farthest from the source. There's a split-second time delay between those two moments. Hager and Kirchner wanted to know how short that delay could be and still correctly send a termite to do battle.

They placed soldier termites on a plastic platform with a gap in the middle almost big enough to slide a dime through. Once a termite stood with its right legs on one side of the gap and its left legs on the other, the scientists triggered a vibration. It shook one side of the platform before the other. The soldiers turned or ran toward the side where they first felt the vibrations.

After repeated experiments, the scientists found that the delay from one leg to another had to last only 0.20 millisecond — a tiny fraction of the length of an eye-blink — to get a termite pointing in the correct direction. This suggested that the delay was comparable to what a termite in the wild would feel from a vibration in the tunnel.

Biologist Peggy S.M. Hill at the University of Tulsa in Oklahoma didn't work on this study. She has, however,studied insect vibrations for a long time. Decades ago, she says, science textbooks told students that solid materials like the ground wouldn't transmit messages clearly by way of vibrations. But clearly that's not true, she notes, as studies like this new one on termites show.

Scientists now estimate that 150,000 different species communicate with vibrations in their nests or other solid surfaces. “We are just beginning to understand how they do it,” Hager told Science News.

Power Words

biology  The study of living things. The scientists who study them are known as biologists.

insect  A type of arthropod that as an adult will have six segmented legs and three body parts: a head, thorax and abdomen. There are hundreds of thousands of insects, which include bees, beetles, flies and moths.

predator  (adjective: predatory) A creature that preys on other animals for most or all of its food.

species  A group of similar organisms capable of producing offspring that can survive and reproduce.

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