a photo would realy help . i suspect it is not a caterpiller and is infact the grub of some kind of beetle as butterflies tend to pupate in the summer on the plant they were hatched on . i hope this helps a little .

It is some sort of moth grub - sorry have forgotten the name - I get them in my garden too sometimes - I usually feed them to the birds (sorry moths). If you enter bright green caterpillar on the internet it will bring up pics of exactly what it is - that's how I found out.

cool thanx mariek

thanks i will have a look on net now