I have been keeping an eye on the Vapoureur egg clutches from last autumn every few days. watched a male being attracted by a female just emerged from her cocoon on the windowsill. They mated and the wingless female laid eggs on the cocoon itself. it is thought that the irritant hairs that the caterpillar weaves on the cocoon silk might offer protection to the eggs and young caterpillars.
It has been eight months and the eggs have overwintered and their development has speeded up as the days warmed. Today, in between showers I had a look and noticed nine open eggs and five tiny caterpillars indicating that probably some of them have already dispersed onto nearby plants.
The other egg clutch nearby is showing no signs of hatchlings as yet.