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We have all been in that situation: The moving boxes are large and heavy, but we are determined to carry them all in one trip, even if that means we can't see where we're going. In the tropics, some leafcutter ants face a similar challenge: carrying a load that is several times their body weight. To make matters even more difficult, carrying oversized weights may create "blind spots" when leafcutter ants transport material on a trail.

This is a recent discovery by scientists at the Smithsonian Tropical Research Institute (STRI) in Panama. Their paper is in the journal Insectes Sociaux.

Leafcutter ants live in societies, and just like humans, deal with waste management, diseases, road design and the everyday struggle of many cities: traffic. Interestingly, some leafcutter ants can carry leaves that are eight times their body weight. However, when leafcutter ants carry an oversized load, they walk more slowly, delaying the nestmates behind, just as big trucks do on a highway.

This phenomenon, known as "the truck-driver effect," can reduce the walking speed of following ants by up to 50%. The reason behind this phenomenon is still a mystery.

Staff scientist Sabrina Amador and her intern Katherine Porras video-recorded ants with and without leaves to see how they used their antennae. In ants, the antennae are in charge of touching, smelling and tasting. Then, they measured the ants and the leaves.

They also performed an interesting experiment: They offered artificial leaves to the ants, consisting of tiny pieces of paper previously dipped in orange juice. This makes the paper attractive to the ants. Once an ant collected an artificial leaf, they carefully cut it with scissors while the ant was still walking, to reduce the load in half, and checked the use of antennae before and after reducing the load.

"When I started observing the ants, what I enjoyed most was paying attention to the small details. The more I observed them, the more questions I had. Then I realized that with any organism we study, the most beautiful thing about science is that we never stop learning," says Porras.

By carefully watching the videos, they discovered that ants with leaves performed fewer antennae taps per step than ants without leaves. Also, the ants increased their antenna taps when scientists reduced the load in half.

Because ants follow their trail by "feeling" with their antennae the chemicals that other ants leave, and carrying an oversized load limits the ability of ants to tap the ground, the ants experience difficulties perceiving the trail accurately. Therefore, carrying larger loads might lead to difficulties in dealing with trail obstacles or surface irregularities. Interestingly, this effect is stronger in larger ants, just as if they were larger trucks.

"What we discovered may explain why, despite having the strength to move larger loads, some ants choose to carry smaller ones," Amador explained. "Leaf-cutting ants are experts at solving logistics and transportation problems, and now we understand more about their load-lifting capacity. As humans have dealt with similar problems, we could learn valuable lessons from their efficiency strategies."

Leafcutter ants enrich the soil and disperse seeds, playing a vital role in America's tropical forests. Remarkably, leafcutter ants can harvest around 1–2 tons of plant material per year. Studying their foraging behavior helps us understand how they navigate the forest, orient back to their nest, or deal with obstacles while carrying plant material. But it also provides insights into how foraging could influence the rate of plant material collection and its broader effects on nutrient cycling and forest dynamics.

Ant movements and their efficiency have also inspired the construction of different robots, and their study deserves further attention in the future.