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Fire ants build small sand siphons to feed on without drowning

The death threat is no obstacle for some hungry fire ants. To escape drowning while feeding on sugary water, black import fire ants built sand siphons that moved the water to a safer place.

A number of animals, including birds, dolphins, primates, and even ants, use objects as tools (SN: 12/30/19; SN: 6/25/20; SN: 6/24/19). Ants often use debris or grains of sand to transport food. But this is the first time it has been observed that insects adjust the use of tools to build relatively complex structures in response to a problem, the researchers reported on Oct. 7 in Functional Ecology.

In the wild, imported black fire ants (Solenopsis richteri) typically eat honeydew produced by aphids. In the lab, entomologist Jian Chen of the U.S. Department of Agriculture's Agricultural Research Service in Stoneville, Mississippi, and colleagues provided the ants with containers of sweetened water. Insects have a hard, water-repellent outer shell called a cuticle, and they can usually float on a liquid, and for sure, the insects floated and fed smoothly.

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The researchers then reduced the surface tension of the water with a surfactant to make it difficult for the ants to float. While some ants drowned, most stopped entering the bins and instead used grains of sand placed nearby to build structures that led from the inside of a container to the outside. Those structures acted like siphons. Within five minutes of building one, almost half of the water was pulled out of the sand path, allowing the ants to feed safely.

“The fact that ants are building small siphons is new and interesting,” says Valerie Banschbach of Gustavus Adolphus College in Saint Peter, Minnesota, who did not participate in the study. The "flexibility of insects to act creatively in response to a situation suggests that they have higher cognitive abilities than is traditionally believed."

In this time-lapse video, observe how most imported black fire ants avoid drowning using grains of sand to build relatively sophisticated structures around containers with sugary water.. In experiments, the ants took more than 90 minutes to move the sand to the bins and do the construction work. These structures act as siphons to draw water from the containers and to a safer place for the ants to feed.

It is unknown how the insects were able to feel the change in the surface tension of the water. Some ants that initially drown could release chemical messengers, Chen says, or maybe the ants like a difference in water or a combination of both.

Black imported fire ants are native to South America, but have gone to parts of North America where they are considered invasive. Insects can damage crops such as corn, soybeans and okra and can also sting humans.

One of the main goals of the project, Chen says, is to develop new pest control measures by better understanding the behavior of ants in their natural habitat. Researchers say different types of surfactants are often added to help them spread better, so ants could be exposed to similar conditions in nature as they were in the lab.

For now, Chen is content to marvel at the laborious insects. “Ants are so amazing,” he says. "We just scratched the surface of the ant world."

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