Two webworms in the genus Loxostege, can cause severe damage to alfalfa. Eggs are deposited in masses on the leaves of food plants with as many as 50 eggs per mass.
Younger larvae are green to yellow and are hairy with many black spots.
Full-grown larvae are approximately 1 inch long, are dark green to black, and have a light line running down the center of the back. Each body segment has three dark spots, each bearing one to three bristles. When disturbed, the larvae may retreat into tubular webs which they have spun, or they may drop to the ground. Webworms overwinter as larvae in the ground adjacent to their fall food host. Moths emerge in early spring and lay eggs on leaves of host plants.