Q: My azalea had caterpillars clustered at the tip of the limb. They have red heads and red feet.
A: Azalea caterpillar, Datana major, is an occasional autumn pest of azaleas. They defoliate random azalea limbs but they will not kill the plant.
If you thump a nearby branch, this caterpillar will hold both ends of its body aloft to make a “C” shape. Any product containing Bacillus thuringiensis (B.t.) click for sources) will control these caterpillars safely.
You can spray them as you see them or simply wait for natural predators to kill them. Hornets and paper wasps find these caterpillars a delicacy.
If you are interested in identifying caterpillars as a hobby, “Caterpillars of Eastern North America” by David Wagner (Princeton University Press, $29.95) is a marvelous reference, filled with colorful pictures.