The ants go marching to option one, hurrah, hurrah

By: Caroline Schaefer

Previous studies on humans found that we memorize the first and last items of a list more easily than the items in the middle. Studies using bees determined that they preferred the items encountered last, and testing using pheromone presence was found to influence motivation towards an item. Pheromones are released from an animal to communicate information to others like food availability. Ants also use pheromones as a guide which is like using your favourite candle to study better for a test; every time you study with the same candle, you will be able to remember the information better. In a recent study led by Felix Oberhauser at the University of Regensburg, a team of researchers tested the use of pheromones and the order in which information was presented in ants as this had not been done before.

In order to achieve this, the researchers set out to test the effects of pheromone and scent use on the path that ants chose to take to a sugar snack. To train the ants to strut their stuff to a reward, a straight runway was built to introduce the ants to the rosemary and lemon scents, as well as the extracted pheromone and a mixture of diluted pheromone. A diluted pheromone mixture was also used so that the pheromone in it would be at more of a normal level to replicate how it would naturally appear as the extracted pheromone would be stronger. The straight runway was set up to have either a pheromone or a diluted pheromone mixture on the entire length of it, followed by additional rosemary or lemon scent at the very end right before a sugar reward. This resulted in four possible combinations of runway layouts. Half of the ants repeated this routine twice in order to familiarize them with the scents more than the others. Next, testing occurred where a Y-shaped maze was used to see which smell the ants liked better without using any pheromone or reward at the end. By removing all other scents, the ants would have to choose which fork in the path they liked best only based on the rosemary or lemon scent. The bottom of the Y did not have any scent on it, but the arms of the Y were randomly assigned as rosemary or lemon. If the ants crossed the fork in the maze, it was counted as an initial decision and if the ants made it all the way to the end of a fork it was counted as a final decision. This was repeated for each ant a few times to make sure that they were sure about their choice.

The results showed that using pheromones to guide the ants down the path did not affect which fork the ants chose. Unexpectedly, the ants chose the fork which had the first scent they were introduced to for the straight runway. Interestingly, if there were no scents at all the ants seemed to prefer the left fork of the maze. From these observations, the first presented odour cue (rosemary or lemon) strongly influenced which direction an ant chose to go in the maze, regardless of if pheromone was used or not.

The researchers found that much like humans and other vertebrates who can memorize the first and last items of a list better, ants prefer the option they are given first even though this seems to go against logic as it requires a longer-term memory than the option given last. This study helps people to have a better understanding of animal behaviour and how similar it can be to human behaviour. Unlike the saying “first is the worst, second is the best”, ants can agree with us that first is best.

Oberhauser, F. B., Bogenberger K., Czackes T. J. (2022) Ants prefer the option they are trained to first. Journal of Experimental Biology. 225, jeb243984.