My 5-year old son has recently become fascinated by ants. He watches them trailing outside and follows them to and from their nest. He asked me how they know where they’re going and where the trail is. I decided to consult an expert. A.P., Dedham, MA

The answer is pheromones. When a worker ant is out foraging for food, it is constantly releasing a chemical odor, or pheromone, as it goes. When the ant finds a good food source, it leaves a pheromone trail as it returns to the nest to recruit more ants. Those ants are then able to follow the first ant’s scent trail back to the food. Of course, as they do so, they are also laying down scent, so the trail becomes even more obvious the more it is traveled.

Some Ants Travel on Three-Lane Highways

Ants are excellent traffic engineers. They design the route to food, then straighten it and add short cuts as needed. They maintain the route and adjust it to accommodate the traffic volume and speed. Some German researchers recently did an interesting study of just how ants follow trails. They found that ants have “trunk trails” which are the main routes in and out of the nest. Each trunk trail worked as a three-lane highway. When there was little traffic on the trail, the ants tended to walk right down the middle. But when traffic picked up, they spread out and maintained two-way traffic.

Ants leaving the nest went to one side of the path; ants returning to the nest with food occupied the other side. Incoming ants moved faster because they were carrying food and they also had important trail information to deliver to fellow workers. The center lane was where ants met. If an ant was moving too slowly, other ants passed it, usually on the right. When traffic on the trail increased, the ants moved faster and the trail widened out to accommodate more ants.

If Only Our Roadways Moved as Efficiently

But no matter how fast they went and how many ants occupied the trail, there was never a traffic jam. Objects in the trail such as a leaf or stone would be quickly picked up and moved to the side so as not to slow traffic. There was the occasional collision, but traffic was only halted briefly while the ants involved exchanged traffic information using their antennae, and then moved on.

In pest control, we can use ants’ trails to our advantage. A trail is a good location for ant bait. The ants can hardly ignore the bait and will soon be carrying it back to the colony. Also, following an ant trail will often lead us to the nest where treatment can eliminate the entire colony. Still, we have to marvel at the accomplishments of nature’s tiny traffic engineers.

[Source: Inside Science by Joel N. Shurkin]