Bugs on my bean sproots
 

Some new beans sprooted, and something was chewing on the leaves.
I'm finding little maggot like creatures chewing on the bean sproots.
On a couple they are turning the leaves to lace. One had it's first
true leaves completely consumed. Others I have managed to save by
picking them off.

Any ideas as to what these are and some sort of prevention?
I have peas started well and some other seedlings sprooting, but they
seem to like the beans first.

Dave.