THE altruism of ants knows no bounds. Not only do pharaoh ants lay trails of pheromones that lead their nest-mates to food 鈥� it now seems the considerate insects also put up chemical 鈥渘o entry鈥� signs in front of unfruitful foraging routes.
Elva Robinson and her colleagues at the University of Sheffield in the UK observed foraging pharaoh ants 鈥� Monomorium pharaonis, a pest in kitchens worldwide 鈥� and were struck by a mystery. 鈥淭hey seemed to know in advance of a junction in their foraging route that some routes were not worth bothering with,鈥� she says. The ants tended to veer away some 3 centimetres ahead of a fork leading nowhere.
To find out why, the researchers allowed the ants to forage and lay trails on a paper surface. They then cut out the paper from a point immediately after the fork on a barren branch and laid it on one branch of a fork where both branches had previously led to food. The other branch received a fresh piece of paper. They found that 71 per cent of ants chose the control 鈥渃lean鈥� branch and the remainder did a U-turn back to the nest, suggesting that the ants use a pheromone repellent to mark unrewarding routes. (Nature, vol 438, p 442)
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If this is confirmed, Robinson says a synthetic version of the pheromone might make a good pest control, perhaps to keep ants away from food cupboards.
