Dunno. I've only collected one sort.
And I've only done it in france. I've never been able to collect enough in England.
( Dr. Shambolic je suis charlie, Tue 16 Jun 2009, 18:40, archived)

I heard if you smash one up with a hammer all the little bits regrow as snails

( glued eel /questions/questionsyoudliketoask/post1648081, Tue 16 Jun 2009, 18:43, archived)