When it comes to spotting potential enemies, ants have a nose for it — literally, with an amazingly precise sense of smell that can identify intruders threatening their colonies, even if those intruders are other ants.

Researchers have always suspected that ants use their body odors — in the form of pheromones — to organize themselves into specialized classes in their colonies.

Now, researchers have found they utilize their powerful smell sense to distinguish chemical compounds on other ants' bodies, even when those compounds are amazingly similar to their own, with the result that they can quickly identify friend from foe.

It allows an entire colony to quickly spot and kill potential intruders, researchers from the University of California, Riverside, write in the journal Cell Reports.

"Until now, very little was understood about how ants use olfactory detection of pheromones to recognize individuals belonging to different castes or different colonies in their societies," says Anandasankar Ray, neuroscientist and UCR entomology professor, who led the study.

"What we wanted to study was how ants detect sophisticated pheromones which organize their behaviors efficiently into colonies, and help recognize individuals from different castes, the queen, and nonnestmate intruders," he explains.

The researchers tested for hydrocarbons present in the hard exoskeletons of worker ants and queens previously suspected as serving as pheromone cues.

The compounds, although very low in volatility, could be detected with great sensitivity by the ants' specialized antenna sensors, the researchers found.

The ability to sense such a wide range of hydrocarbon components is probably a special evolutionary property of social insects, they suggest.

"Using this high-definition ability to smell 'ant body odor,' the ants can recognize the various castes in the colony as well as intruders," Ray says.

Because they need to sense only very few molecules of hydrocarbons on another ant's body, individuals can recognize ants very close to them within a crowded colony.

"A more volatile body odor cue would be confusing to associate with an individual and could overwhelm the olfactory system of the colony members by constantly activating it," Ray explains.

The hydrocarbons and pheromones might be acting as a sort of "chemical barcode," the researchers say, allowing individual ants to identify and recognize other ants in the nest and their status as workers or queens — or perhaps invaders.

"This is a remarkable evolutionary solution for 'social networking' in large colonies," Ray says.

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