Study Finds Certain Ants Excel At Avoiding Traffic Jams

By Nicholas Gerbis
Published: Monday, November 4, 2019 - 5:05am

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Ants running on a bridge
Emmanuel PERRIN/CRCA/CNRS Photothèque
Ants running on a bridge.

Ants get a bad rap from picnickers, but drivers might be able to learn a thing or two from our six-legged friends, especially during rush hour.

The natural world teems with animals that move in groups, from flocks of birds to herds of cattle to schools of fish.

But ants, like humans, belong to a more exclusive club: animals that travel in congested, two-way traffic.

When ants find large food sources, many species will lay down a chemical trail for other ants from their colony to follow. These trails can fill up quickly and flow with hundreds of ants per minute.

To see how the social insects avoid gridlock, researchers turned to the European supercolony of Argentine ants (Linepithema humile), an invasive species that has established itself around the world, particularly in Mediterranean climes.

The scientists studied the insects as they crowded across a bridge to gather food and return it to the nest. To control ant density, the scientists varied the width of the bridge between 5, 10 and 20 millimeters and the number of ants from 400 to 25,600.

Co-author Sebastien Motsch, an associate professor in Arizona State University's School of Mathematical and Statistical Sciences, said the creatures changed their speed and behavior to avoid snarls even when crammed into the densest of traffic.

chart comparing traffic as a function of density in ants and humans
Audrey Dussutour
Comparing traffic as a function of density in ants and humans.

"Surprisingly, it appeared that a traffic jam never occurred, so they always managed to nonetheless keep flowing somehow," he said.

The research appears in the journal "eLife."

Motsch specializes in studying how individuals interact and self-organize without some central authority to direct them.

Unlike humans jockeying for position on the road, ant "commuters" cooperate to accomplish a mutually beneficial goal, so optimizing their ability to forage while avoiding congestion is more survival skill than convenience.

Understanding how Argentine ants manage to keep on trucking through the worst potential jams could have widespread applications beyond traffic engineering, in fields involving dense flows of agents, particles or packets of information.

Ants in general appear to share beneficial reinforcement mechanisms that help them adapt to situations involving masses of bodies. Carpenter ants spread out to avoid trampling each other when trying to escape through a narrow door. Fire ants know how to stay out of each other's way during construction projects. Garden ants excel at avoiding bottlenecks.

Motsch and his colleagues next hope to discover the mechanisms behind the Argentine ants' self-regulation. But doing so could require tracking each ant's behavior individually — no mean feat when observing thousands of 2-3-millimeter-long creatures scurrying over and around each another.

"This kind of tracking is possible. But, in an environment where it's so crowded, it's really challenging," said Motsch.

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