Ants Use Past Experience to Make Decisions for the Future

The decisions faced in daily life by ants may seem insignificant to humans, but where the tiny insects look for food and what they choose to eat can have a big impact on the survival of the ant colony as a whole, and the ants, it turns out, are keen enough to prioritize their decisions to benefit the colony at large, according to Arizona State University researchers.

Writing in the journal Biology Letters , ASU researchers Taka Sasaki and Stephen Pratt report that ants can change their decision-making strategies based on experience and that they can use that experience to weigh different options.

The pair have spent years researching insect collectives, and the goal of their latest study was to understand how the collective decision-making process arises out of "individually ignorant" ants.

"The interesting thing is we can make decisions and ants can make decisions -- but ants do it collectively," said Sasaki. "So how different are we from ant colonies?"

The Temnothorax rugatulus ant colonies used in their experiments have a natural preference for their nest to have small entrances and low levels of light exposure. For their experiment, Sasaki and Pratt presented the ants with two sets of nests.

In one scenario, the entrances of the nests had varied sizes, and in the other scenario, the nests' exposure to light was manipulated. Because these ants prefer both a smaller entrance size and a lower level of light exposure, they had to prioritize.

"It's kind of like us humans and buying a house," said Pratt, an associate professor at ASU. "There's so many options to consider -- the size, the number of rooms, the neighborhood, the price, if there's a pool. The list goes on and on. And for the ants it's similar, since they live in cavities that can be dark or light, big or small. With all of these things, just like with a human house, it's very unlikely to find a home that has everything you want."

Because finding the perfect habitat is impossible, the ants make various tradeoffs and compromises, just like humans would do when selecting a place to live.

The researchers became fascinated as they observed collectives of hundreds of ants seemingly reach a consensus and move into one home versus another.

"You have hundreds of these ants, and somehow they have to reach a consensus," Pratt said. "How do they do it without anyone in charge to tell them what to do?"

He suggested that the individual ants function similarly to individual neurons in the human brain; the individual neuron and the brain as a whole both play a role in decision-making, but no one understands how every neuron influences a decision.

"This helps us learn how collective decision-making works and how it's different from individual decision-making," said Pratt. "And ants aren't the only animals that make collective decisions -- humans do, too. So maybe we can gain some general insight."