In article ,
says...

hehe. probably some of them, but if they
don't crawl far before spinning there's not
much place for them to go in this particular
patch. if they will use the underside of rocks
then i can likely find some of them (and the
raccoons will find some of them too).

http://horticulture.oregonstate.edu/...hite-butterfly

The problem is their pupation on wild hosts.

You can get them in the garden, but the wild mustards in the district are a
little harder to find.