Ant colonies can be very crowded spaces that require elaborate forms of cooperation. While some are nursing, others are collecting food and protecting the nest. And then there are strangers and intruders. Researchers trying to understand how individuals identify fellow members of their colony have discovered that there’s a distinct ant body odor that separates family and friends from foes. The findings are published in Cell Reports this week. 

Among insects, ants have evolved some of the largest families of odorant receptor genes. With more than 400 of these genes, they have a high-definition sense of smell. But how they use this olfactory detection of pheromones to recognize others in different castes or colonies isn’t well understood.  

So, a team led by Anandasankar Ray from the University of California, Riverside, investigated the neurons in the antennae of female Camponotus floridanus worker ants in lab colonies collected from Florida’s Long Key and Sugar Loaf Key. They focused on the ants’ responses to chemicals on the outer shells (called cuticles) of others. Low volatility hydrocarbon chemicals, in particular, are thought to be pheromone cues; anything more volatile might overwhelm the olfactory system by constantly activating it. “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 non-nestmate intruders,” Ray says in a statement. 

The team was surprised to find that, not only is the presence of hydrocarbons detected sensitively by the ants' specialized antennal sensors, but they can even discriminate between hydrocarbons that are only very slightly different. "This broad-spectrum ability to detect hydrocarbons by the ant antenna is unusual,” Ray says, “and likely a special property of social insects.” Each ant cuticle contains a mix of several hydrocarbons, and the specific blend acts as a chemical barcode to help ants recognize various castes within their nest as well intruders. "This is a remarkable evolutionary solution for 'social networking' in large colonies," he adds.