Larvae develop into adults by going through a series of progressive molts through which they increase in size. Instars are the stages between each molt. Male larvae go through five instars (females, through six) before entering the pupal stage.
When population numbers are dense, larvae feed continuously day and night until the foliage of the host tree is stripped. Then they crawl in search of new sources of food.
—“Gypsy Moth,” Forest Insect & Disease Leaflet 162, US Department of Agriculture Forest Service, 1989