They are large moths that are primarily white and covered with black specks. The larvae are very hairy caterpillars that reach a size of two inches or more when mature. Saltmarsh caterpillar larvae can be distinguished form other hairy type caterpillars by examining the head capsule, which is dark brown with a pale yellow streak down the center . The eggs are laid in large masses that are not covered with hairy scales like beet armyworm masses. In some masses there is but a single layer of eggs, but other masses may have two or three layers.
Larger larvae scatter out and feed individually on leaves.
Although a large saltmarsh caterpillar can eat an entire cotton leaf in an amazingly short period of time, larvae are rarely numerous enough to require treatment. Occasionally, scouts may find a dead or dying saltmarsh caterpillar that is stuck to the leaf in a mass of white, cottony webbing. This is a caterpillar that has been parasitized by a small wasp whose larvae emerge from the caterpillar before spinning a group cocoon. One of the most distinguishing characteristics of this moth is the triagular, jet-like shape in which it holds its wings when resting. The wings are a creamy yellow to yellowish brown in color and are crossed by a couple of wavy brown lines.