Among the more remarkable of the notodontid caterpillars are those of the kitten moths of the genera Furcula and Cerura. The caterpillar, which feeds on willow, hatches from a smooth, black hemispherical egg in July. The tiny creature that emerges is black, with two long tails, which it waves from side to side if disturbed. As it grows, the tails become relatively shorter, though they are still long in the final instar. The caterpillar develops a disruptive colour scheme. When the caterpillar is disturbed, it raises its head and tail up, hunching up its shoulders (or rather its thoracic segments), and spreads its two tails in an alarming posture. At the same time it thrashes its head and tails from side to side, while a grey, wriggling wormlike process is extruded from each tail. When ready to pupate it scrapes little particles of wood from the bark and incorporates them into an extremely tough cocoon, which is hard for even a penknife to break into. Winter is spent in the cocoon, and the moth emerges in June.