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Hi Gang,
A pretty weird question I know, but is it known if final instar Purple Hairstreak larvae typically walk all the way along the branches and down the trunk of Oaks when ready to pupate, or just drop off from their final eating place? Energy-wise, it would seem a good idea to do the latter and they may be predisposed to fall off during their "wanderlust" period prior to pupation? The reason I ask is that there are a couple of large Oak trees which hang over a wall near my workplace... almost half of the canopy overhangs the road and I have often wondered how many caterpillars would end up on the tarmac if they just fell off. I do have a brief look as I walk past, but have never seen any. Not surprising I suppose, but if they just drop off, there could potentially be hundreds of final instar larvae in the road at certain times. If it is known that they just "let go" and take their chances, I wonder if this is likely to be at a particular time of the day. Apologies for such a random question, but it is something I have never read or heard about before. I'll get my coat

Somewhere in the dark recesses of my brain, there's a vague recollection of reading somewhere that they do just fall from the branches, although I can't guarantee I've not just invented this!

I believe that they prefer to walk down, based on the fact that in captivity they wander about once ready to pupate. They can move pretty fast - wouldn't take them long to descend. Also I know one excellent site where the south facing boughs overhang a river. It presumably wouldn't be such an excellent site if they dropped off into the water! However that's not to say that some might not drop off if their wandering isn't to their satisfaction, and I have heard anecdotally of one landing on someone.