Ants learn faster on caffeine

Ants that drink a caffeinated solution can locate sweet rewards faster than un-caffeinated ants, suggesting the drug boosts learning.

To see how Argentine ants (Linepithema humile) respond to caffeine, researchers created an ant-sized arena on a sheet of printer paper in the lab. They then placed a drop of sugary solution on the paper for an ant to find. Some solutions had no caffeine, while others had low, moderate or high amounts, but all were placed in the same location.

“We took a bunch of measures of their paths and how fast they were at finding the food source to assess if caffeine is actually improving their learning,” says Henrique Galante at the University of Regensburg in Germany. Of the 142 ants in the study, each was given four tries.

The ants who received low or moderate doses of caffeine took a more direct path to the sweet treat with each trial, suggesting they had successfully remembered the location of the reward. Ants without caffeine took more meandering paths that did not improve over time. Galante emphasises that this isn’t about making the ants move faster, but more efficiently: caffeine had no impact on the ants’ pace but did reduce the twists and turns they took to get there.

The researchers found that more caffeine isn’t always better, though. Ants who drank the lowest dose – 25 parts per million (ppm), which the researchers say is similar to caffeine levels found naturally in some plants – improved their search time by 28 per cent. Ants that got the moderate 250 ppm dose – close to an energy drink – were even more adept, dropping search time by 38 per cent. But the highest dose, 2000 ppm, proved fatal.

Because Argentine ants are a widespread and costly invasive species, Galante says the work could inform efforts to control them. His team is currently testing caffeine-laced baits in the field in Spain with the hope that the drug will boost ants’ ability to learn the bait location – and in turn, help control ant numbers while using less poison.