Such an interesting question I decided to look this up. In my moth book 'The Field Guide to Moths of Great Britain and Ireland' it says that the larval food plants are "Most native broadleaved trees and shrubs, including birches, Hazel, sallows, hawthorns, blackthorns, elms, oaks, and bogmyrtle, and many cultivated bushes ..."
Personally I've seen them on Bramble and a few weeks back on Broadbean in a farmers field. I would imagine that they will find a food plant before they pupate as well, so that when they emerge they are where they need to lay eggs. Once the eggs hatch as with many caterpillars they will travel around until they find something they are willing to eat. That is if the place they have hatched doesn't supply what they need, other wise I suppose they will just stay on that 'tree' or shrub.
Which sorta brings up a question I've wondered, how exactly does a caterpillar know its food plant from other plants, can it smell them? I've raised a few caterpillars of moths and found that they seem to know which plants to get on and try, without taste testing...lol
I'm sure someone will come along that knows more than I do...be curious to see what the 'experts' say
Thanks for your reply, do you know how far they can travel in search of food? They are on his Strawberry plants which are in tubs and a good twenty/thirty feet from the nearest trees.......
I don't know how far they can travel, I can say that they don't do well if they don't eat within 24 hours. So I suppose as far as they can go in that time. I've no idea how fast they move but its surprisingly quick and they are agile once they get it in their heads to move...lol It's just my opinion based on what I've observed but I'd say that distance you're talking about would be a cake walk if they wanted to get there.
The vapourer I saw on the Broadbean was right at the edge of the field and had easy access to nettle, bramble, then trees if he had chosen to, so that large a variety of food plant probably means these never have to travel very far.
Maybe one of the 'Mothiologist' types from NHM will see this and have more info. How many mph can a caterpillar travel, surely I could get a government grant to study this ...