Caterpillars

Today's question - how long is a caterpillar a caterpillar? I'll have to find out. We have the most gorgeous tiger striped caterpillars en masse on our weedy 'patio', the weed they are on being groudsel. Now I had meant to go out and clear it before the groundsel set seed but now we're busy watching the caterpillars to see when they turn into chrysalises (or is it chrysali??). Apparently they are the larvae of the cinnebar moth, a red day-flying moth that's rather attractive we think. So no clearing yet -grrrr.