Beet armyworm larvae can vary from light green to nearly black. They have four pairs of abdominal prolegs and a dark head capsule. Many fine, white wavy lines run along the back, and a broader stripe occurs along each side. There is usually a distinctive dark spot on each side, just above the second pair of true legs. Females lay eggs in masses, covering them with hairs and scales. Eggs hatch in a few days and larvae feed for about three weeks, sometimes spinning slight webs over the foliage.
Source of information
J.P. Michaud, KSU Entomology
Pest photo source
Phil Sloderbeck, KSU Entomology