Behavioural ecology: the age of insects

Like people, insects have varying personalities. And, also like humans, they become more predictable in their behaviour and more set in their ways as they age. But they differ from us in one surprising way: individual insects become more active as they move through adulthood and grow old.

These fascinating observations about insect behaviour come from a study of wild field crickets in Spain, published in the journal Behavioural Ecology. "Even animals that only live for a very short time show signs of ageing, just like humans," says David Fisher, one of the scientists from Exeter University who carried out the research. "Our results show that behaviour in field crickets tends to become more ingrained as the individuals age."

The study took place in a meadow wired up with 140 video cameras to record the lives of an entire population of crickets over two summers. Altogether 582 individual insects were caught, tagged, subjected to a series of "personality tests" and then released back into their home burrows. The tests, which took about an hour, were carried out in a mobile lab. The researchers put each cricket into a tube, where they measured its activity level and boldness or shyness in exploring its temporary environment. The insects, whose adult lives last up to three months, were recaptured and reassessed every few days to determine changes in personality as they aged.

"The personality differences between individuals are quite large and they persist through life," says Tom Tregenza, the project leader. "The additional finding that they become significantly more active as they age came as a surprise."

He speculates that this increased activity, coupled with more exploratory behaviour, may indicate greater willingness to take risks by older crickets that have already reproduced. They have less to lose than when they were younger.

The field cricket is a common sight and sound across southern Europe, as the males "chirp" outside their burrows to attract females by rubbing legs against wings. In Britain, where the species is in decline, conservation body Natural England is now implementing a species recovery programme to bring English crickets back from the brink.

Photograph: wildcrickets.org

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