Superlatives among giant moths are frequently mixed up because three different measurements circulate. Wingspan is the tip-to-tip distance, and is greatest in the neotropical white witch, Thysania agrippina, at roughly 28 to 30 centimetres. Wing surface area is the total two-dimensional area of the wings, and by that measure Coscinocera hercules leads, with female wings spanning around 27 centimetres across a far broader plan than the white witch's narrow ones. Body mass is different again: the heaviest moth recorded is the Australian giant wood moth, Endoxyla cinereus, a cossid, at over 30 grams.
The sexes differ markedly. Females are heavy and broad-winged; males have narrower forewings and long trailing hindwing tails that add several centimetres to overall length. Like other saturniids the adults have no functional mouthparts and do not feed, so the winged stage lasts only days.
Larvae feed on rainforest trees, notably bleeding heart, Homalanthus. Reported figures for the largest specimens vary between sources because measurement conventions differ, so any single number should be read as approximate.