I've come across a new category of bugs, namely bugs that stab and poison then suck their prey dry. This category includes Assassin and Ambush bugs (family Reduviidae) and Damsel bugs (family Nabidae). I think that the bugs pictures here might be a nymph (left) and adult Damsel bug. You can see their sucking parts, folded back in the nymph and pointed down in the adult. Perhaps they're male and female adults of the same species or different species. I don't know yet. All of these killing bugs can be found in profusion in grassy fields.