Mike O'Shea, age 12, of St. Louis, Mo., for his question:
ARE ARMY ANTS REALLY BLIND?
Ants are social insects that live in colonies centered around their egg‑laying queen‑mother. Most species share a family nest and never wander very far from home. The army ants of South America and the driver ants of Africa live like savage bandits, always on the move. They are feared more than lions and leopards. Actually they are mindless mobs, and most of them are blind.
A colony of army ants may include a million members. Every month or so, they stop their fearsome marches while the large, wingless queen lays from 25,000 to 35,000 eggs. The colony includes large soldier ants with strong jaws plus a multitude of small workers. All of these ants are blind.
The colony also includes large males that look somewhat like fierce wasps. These ants have wings and large compound eyes. Sometimes they go off with groups of workers and soldiers to start a new colony. A young queen may be selected from the home colony or from a neighboring colony.
The egg‑laying rest period lasts until the new brood is ready to travel. Then the blind soldiers prepare to lead the blind workers on a fierce foray through the forest. They scout ahead, placing scented chemicals to mark the way. The workers stream forth like a dark, crawling river. They travel shoulder‑to‑shoulder while the soldiers march along the sides of the column.
It seems impossible, but all this military precision is done without eyes. The marching army depends upon the scents of the soldiers and of each other. In addition, each army ant has a built‑in instinct to follow the leader. The marching column is so crowded that each ant can scent and touch its neighbors‑‑and when the leaders move ahead, all the rest follow.
The teeming army is famished for meat. Birds and other animals that can move fast enough hurry away to safety. But snails, snakes and other slowpokes are left in the path of the advancing horde. Ants swarm all over them and devour their flesh in minutes. The blind ants also detect their food by scent and touch.
Usually blindness is no handicap to the army ants. But sometimes their path must circle around a tree or other obstacle. If the trail makes a full circle, the column may be led around and around. The circling marchers grow weak from hunger and soon die. Maybe the whole sightless column could be misled into a suicidal circle of this sort.