Egg recognition: Its advantage to a butterfly

Ovipositing females of the pipevine swallowtail butterfly, Battus philenor, detect the presence of eggs laid by other females on their host plants. The presence of eggs on a plant inhibits oviposition by a female that discovers it. The selection pressure responsible for the evolution and maintenance of discrimination against plants with eggs appears to be lower survival from egg to adult of eggs laid on plants already containing eggs than on plants without eggs.