Eggs are 2 mm long and near-ellipsoidal in shape, with the shell smooth and unsculpted. Eggs are usually laid in clusters of 3–200 in the foliage of the upper crown, while a small number are laid on the trunk near the ground. After hatching the shells are consumed over a period of two to three days by the young larvae, a process that triggers their plant-feeding response and so plays an important role in their development. Incubation of the eggs laid in mid-summer takes about 18 or 19 days, and 21 to 28 days for those laid in winter.
Larvae go through six moults and are highly
gregarious till the end of the second moult. After the second moult the larvae acquire their gaudy colouring of bands of blue, green and yellow spots on a deep maroon ground colour. Full development takes from 6 to 8 weeks, and when mature the caterpillar is between 100 and 125 mm long. The mature larvae or caterpillars crawl to the ground and search for a patch of soft soil, burrowing to a depth of about 50 mm. After several days the skin splits along the dorsal line.
Pupae are dark red at first, but after a few days becomes dull black and hard. The pupal stage lasts from 5 to 6 months. When the moth is about to emerge the pupa works its way to the soil surface, the pupal case splits and the moth emerges. The moth climbs a small distance up a tree or shrub and then allows the wings to expand and harden, a process taking some 30 minutes. Adult moths survive for only a few days, long enough to mate and for the female to lay about 200 eggs on a suitable food plant.
Adult moths show considerable variation in size, but on average have a 125–150 mm wingspan, the body being about 50 mm long and densely covered in silky hair. Colouration and markings differ only slightly between the sexes. Antennae of the male are broadly comb-like (pectinate), while those of the female are almost linear and only slightly serrate. ==References==