Q: What enables ants to find the nearest picnic?

A: From one ant to dozens, it doesn't seem to take the critters long to overrun your ham sandwich and ruin your picture-perfect picnic.

It starts with an individual ant, which has left the colony on a scouting mission, says Bob Jeanne, a UW-Madison professor of entomology.

When the ant gets downwind of your sandwich, it orients itself to the food odor, locates the source and chews off a tiny piece. It then scurries back to its colony, secreting a trail of pheromones as it goes.

Pheromones are chemical signals like hormones, except they work between individuals of the same species. Most ants secrete trail pheromones from glands in their abdomen, leaving an invisible, ephemeral path for others to follow.

When the ant returns to the nest, the pheromone excites others inside. They follow the trail to the food source. Each ant that finds the food is rewarded, and marks the trail again on its way back to the nest.

As long as there's food, the positive feedback continues.

- Produced in cooperation with University Communications

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