To produce additional egg masses, the female needs a blood meal. Among biting flies, blood serves as a rich protein source necessary for egg development. In the case of the salt marsh greenhead, protein for the first egg mass is obtained when the predaceous larva eats other insect larvae or small animals, but to lay additional egg masses she must obtain a blood meal. Adult female greenheads move from the salt marsh to nearby -wooded or open areas along the marsh edge to seek suitable blood sources. There they await and attack wildlife, livestock, and people that venture close enough for them to detect.
Females live for three to four weeks in the uplands before they become too weak to bite.
Because of this long life, larger numbers of' blood hungry flies build up in areas near salt marshes. The physical removal of large numbers of flies can reduce this buildup and thus decrease the greenhead fly problem locally. In fact, the traps capture large numbers of blood-seeking flies and if such traps are located at the edge of a marsh or in adjacent uplands where flies concentrate, they serve as a partial control for greenheads. Where single traps capture hundreds of flies per day, a marked reduction in greenhead annoyance results. In Delaware, the use of three to five traps near isolated human dwellings has resulted in almost complete reduction in greenhead attacks.