Determining friend or foe in the ant world is a touchy subject.? New research reveals how carpenter ants screen nest-mates from non-mates with special chemical sensors on their antennae.

Like many social animals, ants rely on chemical communication to direct cooperation, as well as identify intruders.

On their bodies' thin outer lining (the cuticle), ants wear a chemical "ID badge" made up of a unique blend of compounds called cuticular hydrocarbons, or CHCs.

Mamiko Ozaki from the Kyoto Institute of Technology and colleagues were able to isolate these CHC blends from different ant colonies. The researchers covered glass beads - which acted as "surrogate ants" - with nest-mate and non-mate blends and recorded other ants' reactions.

The non-mate blends elicited aggressive behavior, which included "biting, jumping and spraying formic acid" at the surrogate ant, Ozaki told LiveScience in an email message.

Ozaki's team determined that the intruder detector was in the ants' antennae.? Specifically, non-mate CHC blends excite a certain type of small hair-like structures on the antennae called sensilla.

The enemy-recognizing sensilla are relatively thick - 20 microns long and 4 microns wide - and are full of small pores.? Multiple pores are often associated with an insect's sense of smell, but the researchers suspect that the ants need to rub their antennae over another ant to tell whether it is an adversary or not.

"The CHCs are not volatile at ordinary temperature. Thus, I believe that the sensilla rely on contact," Ozaki said.

Interestingly, the sensilla are not stimulated by the CHC blend from nest-mates.? Therefore, discrimination of friend or foe may not require any processing by the ant brain - the antennae may do all the work by only sending out an alert when foreign chemistry is detected.

How an ant's sensilla become desensitized to its own colony's CHC blends is a question that the researchers plan to look into next.?

A paper describing this research will be published in the June 10th issue of the journal Science, but also appears on the Science Express website.

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