When I need to get rid of caterpillars, I have found you stand there flick them into a bucket of soapy water....I know it sounds daunting but I don't know any spray that will deter them. If they are in a web take a stick and open the webbing the birds will eat them.
I think hand-picking them is generally the best solution as well, but you can also use Bacillus thuringiensis (B.t.).
I am going to try the BT and see if this helps, Thanks