Bembidion quadrimaculatumL. is one of the most common carabids in Michigan onion fields and feeds on onion maggot,Delia antiqua(Meigen), eggs and first instars as well as a number of other prey. Laboratory and field experiments were conducted to determine the effectiveness ofB. quadrimaculatumas a predator of the onion maggot. Up to 25 onion maggot eggs per day were consumed perB. quadrimaculatumadult. Consumption of eggs and first instars increased with temperature. Predation was higher when eggs were placed on the soil surface than for eggs placed 1 cm deep (70% versus 17.5%). In field cage studies,B. quadrimaculatumreduced onion maggot numbers by up to 57%.B. quadrimaculatummay therefore be an important biological control agent for the onion maggot.