Army ants are a force to be reckoned with in Central and South American rainforests, frequently raiding other social insects鈥� nests for vulnerable larvae and pupae. A computer simulation suggests that the insects have come up with a strategy to boost the speed and efficiency of their raids, by temporarily storing the food from a raid in a nearby cache.
at the University of S茫o Paulo in Brazil and his colleagues were observing army ants in the Amazon rainforest when they noticed the insects stacking prey that they had pillaged in piles along their foraging trails, far from their 鈥� the nest that houses the queen and larvae and is made out of interlinked bodies of living worker ants.
Biologists first noticed these food stacks, or caches, nearly a century ago. They were assumed to appear because ants became stuck in insect traffic jams on their journey back to the bivouac and simply dumped their loads while waiting for the flow issues to resolve.
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鈥淥n the other hand, the biology of army ants told us that timing is essential for them,鈥� says Lima. When a small raiding party is preying on the young in another species鈥� nest, the element of surprise is important and the entire raid must take place rapidly before the defenders can fight back or evacuate the nest.
鈥淲e thought that caches may somehow accelerate raiding, making them economically viable for the colony,鈥� says P贸voas de Lima.
He and his colleagues generated computer simulations of ant movement during raids and found that raiding ants gathered more food by dumping anything they stole in a cache positioned between a raided nest and their bivouac, then returning to the raided nest to steal more food. However, this advantage worked only as long as the raiding party contained fewer than 100 ants: a larger raiding party didn鈥檛 need to cache food for a speedy and efficient raid.
鈥淐aches may help army ants relying on a limited worker force at foraging fronts,鈥� says P贸voas de Lima. He says Atta colombica leafcutter ants do the same thing with their leaf fragments, dropping them so they can return to harvest more. These two ant species are quite different in terms of their lifestyles, but the caches鈥� purpose is 鈥渢o some extent the same: maximising food retrieval鈥�, says P贸voas de Lima.
at the University of Southern Mississippi, who wasn鈥檛 involved with the research, is curious about which factors 鈥� like terrain and predator presence 鈥� could influence the choices of how and where the ants create caches.
鈥淭here are all sorts of interesting emergent group features that you see here occurring as a result of a bunch of individual decisions,鈥� she says.
Reference: bioRxiv,
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