What caffeine does to ants could change pest control

"The idea with this project was to find some cognitive way of getting the ants to consume more of the poisonous baits we put in the field," says the first author and doctoral researcher Henrique Galante, a computational biologist at the University of Regensburg. "We found that intermediate doses of caffeine actually boost learning -- when you give them a bit of caffeine, it pushes them into having straighter paths and being able to reach the reward faster."

Argentine ants are among the most damaging and expensive invasive species worldwide. Efforts to control them typically rely on poisoned bait, but these strategies often fall short. Colonies may ignore the bait or abandon it before it spreads widely. The research team explored whether caffeine, which is already known to enhance learning in bees, could help ants better remember bait locations and lead more nestmates to them.

"We're trying to make them better at finding these baits, because the faster they go and come back to them, the more pheromone trails they lay, the more ants will come, and, therefore, the faster they will spread the poison in the colony before they realize it's poison," says Galante.

Testing Caffeine's Effects in the Lab

To investigate this idea, the scientists designed a controlled experiment using different caffeine levels. Ants crossed a small Lego drawbridge onto a test surface, which consisted of an A4 sheet placed over acrylic. There, they encountered a drop of sugar solution containing 0, 25 ppm, 250 ppm, or 2,000 ppm of caffeine.

"The lowest dose we used is what you find in natural plants, the intermediate dose is similar to what you would find in some energy drinks, and the highest amount is set to be the LD50 of bees -- where half the bees fed this dose die -- so it's likely to be quite toxic for them," says Galante.

The team tracked each ant's movement with an automated system, measuring both travel time and how direct their paths were. In total, 142 ants took part, and each one completed four trials. Between trials, the ants could unload their collected food, and the testing surface was replaced to prevent them from following their own pheromone trails.

Straighter Paths, Faster Learning

Ants that received only sugar showed little improvement over time, indicating they were not learning the reward's location effectively. In contrast, ants given low or moderate amounts of caffeine quickly became more efficient.

For ants exposed to 25 ppm of caffeine, foraging time decreased by 28 percent with each visit. At 250 ppm, the improvement reached 38 percent. For example, an ant that initially took 300 seconds to reach the reward could cut that time to 113 seconds at the lower dose and just 54 seconds at the intermediate dose by the final trial. The highest caffeine level did not produce the same benefit.

Focus Over Speed

The improvement was not due to increased speed. Instead, caffeinated ants followed more direct routes, suggesting stronger focus and better spatial memory. Their pace remained unchanged across all doses, but their paths became less winding at the lower and intermediate levels of caffeine.

"What we see is that they're not moving faster, they're just being more focused on where they're going," says Galante. "This suggests that they know where they want to go, therefore, they have learned the locations of the reward."

Caffeine did not affect how efficiently ants returned to their nest (how efficiently they traveled back to the nest), although all ants improved slightly over time regardless of caffeine.

A Potential New Tool for Pest Control

The findings suggest that caffeine could play a role in improving pest control strategies for Argentine ants. By helping ants learn bait locations more quickly and recruit more nestmates, caffeine could increase how effectively poison spreads through a colony before the ants detect it.

The researchers caution that more work is needed before applying this approach in real-world settings. Ongoing studies are testing caffeine-enhanced bait in outdoor environments in Spain and examining how caffeine interacts with the poison itself.

This research was supported by the European Research Council, the Deutsche Forschungsgemeinschaft, and the University of Regensburg.