News in Science

Poison-taster ants protect the colony

Researchers have discovered that ants marching into our homes seeking food use a simple strategy to reduce the impact of being poisoned.

According to the study, ants have evolved three successful ways to combat both poisonings and famine, including sacrificing some ants as poison tasters.

The findings, accepted for publication in the journal Animal Behavior, may apply to humans - and not just those with ant invasions - because they show how food can be distributed quickly after a famine, while also guarding against sickness, or even death.

Ants "have evolved to great ecological success over millions of years and hence are likely to have found a solution," says lead author Dr Ana Sendova-Franks.

She says it's also "relatively easy to study experimentally the link between two levels of organisation: the individual and the system."

Sendova-Franks, an associate professor of biometry and animal behaviour at the University of the West of England, and her team collected four Temnothorax albipennis colonies in Dorset and housed them in artificial nests.

The researchers did not give the ants food or water for 48 hours, which is actually a mild deprivation representing "the normal level of hunger of ant colonies in the field," says Sendova-Franks.

Living silos

Some colonies can survive up to eight months of starvation. Before and after providing food on the third day, the scientists tracked each individual worker ant.

During famine, some worker ants that normally were active outside of the colony stayed put, retaining food and getting new food from foragers. When other ants then needed a boost, the stay-at-home ants shared their food using mouth-to-mouth regurgitation.

These "living silos are a completely new discovery," according to Sendova-Franks.

She says "they could act as both testers for food toxicity and also as food storers." These "living silos" tended to be older ants, with younger brood workers kept more out of harm's way.

But those ants weren't the colonies' only defense. Although 95% of workers were fed at least once within 30 minutes of the famine's end, the system of food distribution meant that food was mixed and diluted, again reducing the threat of poisoning.

Since the new food and its distribution were located mostly outside of the colony's centre, the queen, larvae and brood workers can enjoy relative safety, perhaps being fed by the surviving "living silos."

Sendova-Franks says that some species, such as Australia's honeypot ants, even have workers that gorge themselves with sugar and remain inert, providing a kind of (regurgitated) candy in the pantry during lean times.

Poisons set out by humans aren't the only threat. Ants encounter natural toxins too, from new food sources to foods that ferment, so the ant's defensive tactics likely evolved long before the emergence of modern insect repellents.

Network theory

Biologist Anna Dornhaus of the University of Arizona says "this is a ground-breaking study in that it is one of the first to realise the promise of network theory by using this new field and applying it to a thorough dataset - food sharing interactions in ants."

Dornhaus says, "It is interesting to see that interactions between ants are not random, the network is structured, and that through this network food can be distributed so extremely quickly when needed."

Sendova-Franks says she and her team "are motivated by our fascination with ants," some of which can live to be six years old.

She hopes future research will allow people, including irate homeowners, to find "ways of dissuading ant colonies from doing what we do not want them to do," instead of pulling out the poison.