>>1142247they prey on aphids, caterpillars, slugs and the like.
The wasps in particular, lay leggs under the skin of live caterpillars and such, which then hatch and eat them from the inside out.
Gory, but pretty cool; also I finally have one of pic related in my yard to eat slugs and snails, I'll have to keep him away from my berries but it's worth it!