CUriosity: Why and how do ants walk in a perfect line?
In CUriosity, experts across the CU Boulder campus answer pressing questions about humans, our planet and the universe beyond.
This week, entomologist Julian Resasco answers: “Why, and how, do ants walk in a perfect line?”
A group of ants walking in a line. (Credit: Jithin Vijayamohanan/Unsplash)
In the world of ants, order isn’t optional. These tiny insects live in colonies with millions of others, working together as a team to forage, defend their nests and care for their young.
As spring arrives, ants emerge from their winter hiding places and quickly organize themselves into perfect lines, weaving across patios, yards and kitchen floors in search of food for the colony.
Ants are some of the best team players in the natural world, and keeping such a large organization running takes a special kind of communication, said Resasco, assistant professor in the Department of Ecology and Evolutionary Biology. Most of the time, these insects reply on chemical scents, called pheromones, to exchange information with each other. That includes where to find food.
Julian Resasco
When an ant finds a promising snack, it marks its path with pheromones as it heads back to the colony. Fellow ants follow the trail by picking up the scent using sensors often in their antennae. They also lay down more of the same scent along the way to strengthen the trail.
Generally, ants don’t see very well compared to humans. Instead, the pheromone trails help them navigate without getting lost. That’s why they march in a nearly perfect line.
Depending on how good the food source is, ants may choose to secrete pheromones that can stick around for a long time so they can recruit a larger group to help carry it. They could also lay down pheromones that evaporate quickly if the food is subpar or can be quickly gathered up.
“If you look at any individual ant and what they're doing, they seem really dumb,” said Resasco, who has been studying ants, including the notorious fire ants that give people painful stings, for over a decade. “But as a colony, a sum of all these very simple behaviors, they can do pretty amazing and complex things.”
In addition to marking the path to a food source, ants can also secrete chemical signals to alert others in the colony of an approaching enemy.
Different species of ants have different ways of forming their foraging routes. For example, leafcutter ants can build organized lanes of traffic: One lane going up tree branches to the food source and another for those returning with the harvest. Army ants, commonly found in Central and South America, assemble themselves into massive, moving swarms to raid other insect colonies for resources.
“If you see these ant swarms in the rainforests, it looks like the ground is moving,” Resasco said.
But the system isn’t foolproof. If an army ant swarm hits an obstacle, or a small group loses the pheromone track, they may start following one another in a continuously rotating circle called a death spiral. As the name suggests, the spiral ends only when the ants die of exhaustion.
“Ants are the little things that run the world. They're extremely abundant, and they do really important things for our ecosystems and agriculture, such as turning over soil and eating other insects that may be pests,” Resasco said.
He recommended that following a trail of ants and observing what they do could be a fun activity for a sunny afternoon.
“Ants are virtually everywhere we look, and if we pay attention to them, they’re always doing interesting things.”