there are worms on my cherry and plum trees, which are eating windowpane
type holes in the leaves. a google image search brought me to this:

http://www.gardensafari.net/pics/wes...i_hs0_2370.jpg

they call it a "cherry slug", and say it's a sawfly larva, but i can only
find info on it in non-US websites. i live in WA state in the US, so i'm
wondering if this is a native pest, or something that got imported with my
trees (i have no idea where they came from).

will this pest go away with the winter, or do i need to spray my trees now?
is there an effective biological control? or am i reduced to use a soap
spray?

thanks,

-kelly