The Daily Californian Online

Ants More Attracted to Salt Than to Sugar

By James Parker
Contributing Writer
Monday, November 3, 2008
Category: News > University > Research and Ideas

It is common sense that flies are more attracted to honey than vinegar, but when it comes to ants, salt may be better bait than sugar.

In a new study published last week in the journal Proceedings of the National Academy of Sciences, researchers from UC Berkeley, the University of Oklahoma and the University of Arkansas at Little Rock have discovered a correlation between the inland distance of an ant colony and how attracted they were to salt.

"It's a neat idea that something as simple as the amount of sodium that falls from the sky is going to have a noticeable impact on the most dominant insect on the planet," said the study's lead author Michael Kaspari, an associate professor and director of the graduate program in ecology and evolutionary biology at the University of Oklahoma.

To measure the ants' response to salt and sucrose, vials and cotton balls with varying concentrations of the two compounds were placed together in locations at different distances from the coast. The researchers measured the number of ants that were led back to the sample from the colony.

The study, which was completed throughout the past two years at 17 locations in the United States, Costa Rica, Peru and Panama, demonstrates that the ants were most active between 10 and 100 kilometers away from the coast, as indicated by their sucrose use.

Past 100 kilometers inland, where rainfall contains far less salt, the ants became more attracted to salt solutions than sucrose solutions, even when the salt levels were at lower concentrations.

"Right next to the ocean, the ants tended to ignore salt. Once you get 10 kilometers inland, they started to use salt," Kaspari said. "By 1,000 kilometers inland, they were recruiting to salt solutions of 0.01 percent. That's almost pure distilled water with a crumb of salt."

Kaspari said if the ants were cars, sucrose would be gas and salt would be oil. The researchers found that when there was a shortage or an excess of salt, the ants' sucrose use dropped, indicating that they became less active.

Changes in the amount of ant activity can have significant impact on the environment because of the insects' prevalence globally and their role as decomposers, according to the researchers.

"Maybe salt scarcity regulates all animals involved in decomposition," said UC Berkeley integrative biology professor Robert Dudley, a co-author of the study. "People haven't thought of sodium as an ecosystem regulator before."

The researchers plan to advance upon their findings by testing whether adding a salt lick to a sodium-deficient area increases ant activity or affects the ecosystem in general, Kaspari said.

Elements like oxygen, hydrogen, phosphorus, carbon and nitrogen are typically viewed as the most important nutrients in an ecosystem, with salt often being an afterthought, he said.

"The role of salt is surprising in this animal," said UC Berkeley integrative biology professor Robert Full, who was not involved in the study. "It suggests that we need to understand the limitations it puts on an ecosystem ... I think that what's going to happen now is that people will look beyond the carbon cycle."

Article Link: