I come across these every so often in my photographic journey and haven't yet discovered the real story behind them. This one is on a bottle brush (Callistemon) leaf. It seems like a parasite invasion of the caterpillar though I can't be sure. Kyogle, NSW.
CallistemonFungusaustralianbottle brushbrowncaterpillardeaddecaygreengrubsinsectleaflepidopteramacro photoparasitepupapupaesilkwitheredwrinkles