What Are Pheromone Trails and How Do Ants Use Them?

A pheromone is a chemical an animal releases to send a message to others of its kind. Ants have a dozen or more glands that produce them, and a trail pheromone is the one laid on the ground to mark a route. The ant presses the tip of its abdomen to the surface every few steps, leaving a dotted line of scent too faint for us to notice and plain as paint to another ant's antennae.

A single ant's trail is weak and short-lived; depending on the species and the surface it fades in minutes to a few hours. What makes a trail last is traffic. Every ant that follows it and finds the food adds its own scent on the way home, so a route to a good food source gets stronger while a route to nothing fades out. Trails to a permanent resource, a nest entrance or a tree full of aphids, can be maintained for weeks or months, and in some species foragers can tell the outbound direction from the homeward one by the way the scent is laid.

The result is a network nobody designed. Where two trails run to the same place, the shorter one gets reinforced faster because ants complete the round trip sooner, and within a few hours the colony is running the most efficient route available. That is why a trail across your kitchen is usually the straightest line between the entry point and the food.

The trail is the reason baits work. A bait station or gel places a food the ants want, mixed with a slow-acting active ingredient, where foragers will find it. The first ant that does lays a trail home, and the colony does the rest: more and more foragers follow the trail to the bait, carry it back, and share it through the nest, including with the larvae and the queen. Because the active ingredient takes days rather than minutes, the foragers keep working and keep the trail strong until the bait has reached the whole colony. The ants' own communication is what carries the treatment to the nest you cannot see.

The same fact explains why a spray along the trail so often fails. A repellent spray kills the ants it touches and breaks the trail, so the line is gone the same afternoon. The nest, with the queen and the brood, is untouched, and in several of the species common in Texas homes, odorous house ants and pharaoh ants among them, the alarm it sets off makes the colony split and relocate. Two or three trails appear where there was one. When a technician asks you not to spray or wipe down a trail before a visit, this is why: the trail is how the bait gets home.

Researchers are also working on using the pheromones themselves. Synthetic alarm pheromones might disperse a colony from a spot where it cannot be treated; synthetic trail pheromones might draw foragers to a bait faster or lead them away from a sensitive area. Some of this is in use in agriculture for other insects. For structural ant control it is still largely experimental, and nothing on this page should be read as a product we apply.