Second instar Lymantria monacha larva. Melody Keena, USDA Forest Service, Bugwood.org. 

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... fly at night from the middle of July to the beginning of September (exact dates depend on the climate of the region). Nun moths are variable in appearance, with the fore wing ranging from chalk-white, decorated with numerous dark wavy lines and patches, to almost black with flecks of white ( Fig. 1 above). The genus Lymantria can be distinguished from other lymantriine genera by wing venation (Fig. 3), and L. monacha can be distinguished from L. dispar by its compound eyes, which are larger because they fly at night rather than at dusk (Ferguson, 1978). Keena et al. (1998) provides a method for distinguishing each stage of L. monacha from that of L. dispar, the only other Lymantria species found in North America. Males are nocturnal and females release pheromone to attract males (Fig. 4). Adults are most active near midnight. Although females can fly, they usually remain on stems and wait for males. Once mated, the females lay 70-300 Figure 4 Female Lymantria monacha (left) releasing phero- mone and male (right) approaching to mate. Melody Keena, USDA Forest Service, Bugwood.org eggs in clusters of approximately 40 eggs in bark crevices or under lichens on bark (Fig. 5). Females fly more actively after depositing eggs. The nun moth embryo in the egg completes development in 2-6 weeks, but remains in diapause for another 10 weeks. Eggs hatch in early May (Fig. 6). First-and second-instar larvae are capable of wind dispersal over considerable distances (Fig. 7). There are 5-7 larval instars (Figs. 8 and 9), and pupation occurs in July. The pupa is naked and reddish brown, with clumps of light-colored hairs (Fig. 10). Males emerge a few days before the females. For more information on the biology see the summaries by Bejer (1988), Grijpma (1989), and Lipa and Glowacka (1995). ...