Duration of the larval stage is usually four to six weeks. Larvae of the black race present on red mulberry, redbud, and elm in August and September disappeared from webs 25 to 30 days after hatching. The cycle from egg to adult for either race is usually completed in about 50 to 60 days. Occurrence and Seasonal Activity Fall webworm populations vary greatly over the years. In Alabama, webworm activity begins in April and may continue into October 2 .
Seasonal records indicate that, in most years, two generations occur.
Both races are represented, and three separate caterpillar broods usually develop each season. In the Auburn vicinity, the initial brood, which is black race, occurs in late April, May, to early June. In many years, this first brood is light and may go unnoticed. In some years, a second brood of the orange race may possibly occur in some areas. Importance, Damage, and Control Outbreak populations of fall webworm can completely defoliate host trees.