When chemical cues disappear, ants rely on memory

Martin Castorena

When chemical cues disappear, ants rely on memory

Drop a blob of jelly on the kitchen counter, and you might soon see a stream of ants headed straight for the mess. They’re following chemical cues called pheromones, left by their colonymates who found the food first. By following the pheromones, ants can feast on jelly again and again. But a new study suggests that pheromones aren’t the whole story: Ants’ individual memories of the path also encourage these repeat visits. Researchers observed captive black garden ants (pictured) as they discovered and fed on a weak sugar solution. Then they removed the ants, erased the pheromone trails, and added a second, sweeter food source. When they returned the ants to the enclosure, the insects stuck with the original sugar solution even though their previous pheromone trails leading to it had disappeared. Without a chemical map, they relied on their memory of the old route instead of scouting new food, scientists report in the Journal of Experimental Biology. The captive ants missed out on snagging a sweeter meal, but the strategy probably benefits them in nature, where colonies exploit a variety of food sources. Navigating both by pheromone and memory makes them more flexible: Even if rain or time washes away their pheromone paths, they can still access a tried-and-true meal. 

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