Higher productivity at the cost of increased host-specificity when Maculinea butterfly larvae exploit ant colonies through trophallaxis rather than by predation

1. Field studies were made of the benefits and costs of two feeding strategies in the genus Maculinea, whose final-instar larvae parasitise Myrmica ant colonies. Maculinea arion is an obligate predator of ant brood, whereas M. rebeli and M, alcon mimic ant larvae and are fed (like cuckoos) directly by the workers. 2. Samples of > 1500 Myrmica nests confirmed laboratory-based predictions that, by feeding at a lower trophic level, many (4.7-fold) more individuals of M. rebeli and M. alcon are supported per ant colony than M. arion. 3. Because of their efficient feeding, cuckoo species often occupied sites where their phytophagous early larval populations coincided to only a small extent (> 10%) with host Myrmica colonies, whereas all sites supporting M. arion had 50-100% of the phytophagous stages within foraging range of the host Myrmica species. 4. Greater host-specificity was identified as another consequence of cuckoo-feeding. The ecological cost of this is discussed. 5. The feeding of other Maculinea species had not been fully described: the data suggest that M. nausithous is a predator of ant brood and confirm that M. teleius is predacious.