This family is of interest to biological control because of the large number of species that are predaceous. The subfamilies Gerydinae and Liphyrinae are entirely predaceous, while some species of Lycaeninae are predaceous as final instar larvae. Early accounts of biology and behavior of predaceous butterflies were by Farquharson (1922), Clark (1926) and Balduf (1938). The latter reviewed the interrelations between lycaenids and the ants and Homoptera with which they are associated. Species were divided into 6 classes on the basis of food habits and of their relations with ants. In many cases the caterpillars and ants are competitors for a common food supply, and the secretions of special glands of the caterpillars are a kind of bribe to induce the ants to tolerate their presence (Clausen 1940/62).
Predaceous Lycaenidae usually prey on Coccidae (Pseudococcus) and Aphididae, but also on Cicadellidae and Membracidae and the immature stages of Formicidae. In North America, Feniseca tarquinius F. was the first lycaenid found to be predaceous. It fees in all its larval stages only on aphids, such as Prociphilus, Schizoneura, and Pemphigus. Eggs are laid singly among the aphid colonies, always on the underside of the twig. The newly hatched larva spins a loose web over its body, beneath the aphids, that is thought to be for protection. Feeding occurs from underneath. The long hairs of the dorsum of the body entangle a quantity of waxy material, giving the larva a woolly appearance. The larvae seem quite immune to attack by ants that tend the aphids. They have a variable color pattern, due partly to the species of aphid that is attacked. There are 4 larval instars and pupation seems to occur in the trash beneath the tree. The egg, larval and pupal stages take 3-4, 10, and 8-11 days, respectively. There are 3-5 generations annually, and they overwinter as pupae (Edwards 1886, Clark 1926).
Different species of Spalgis are most often found as predators of mealybugs, although they also attack aphids. S. epius Westw. (Aitken 1894) of Asian tropics, lays its eggs among the masses of mealybugs. The flattened, greenish larvae bear a fringe of bristles about the sides and front of the body, and this is used in shoveling the waxy covering of the host onto its back. This covering gives it a resemblance to the host individuals, although the older caterpillars are much larger and resemble syrphid larvae. Only the younger host stages are attacked. Larvae are found within ant nests, feeding on mealybugs which are being held therein. The pupae of Spalgis and Feniseca are peculiar by having a color pattern that is looks like the face of a monkey. The larvae of some Lachnocnema spp. are associated with Cicadellidae, on which they are predaceous. They also feed somewhat on the secretions of the leafhoppers, and may possibly be fed by the ants.
Clausen (1940) noted that the genus Lycaena is particularly interesting because of the interrelations developed between its members and their ant hosts. Oviposition is thought to occur mainly on food plants beneath which ant colonies are situated. The young larvae are entirely plant feeders, but in the last stage they find their way or are carried into the ant nest where they feed on ant larvae and pupae. A pronounced cannibalistic habit is shown by the larvae during the plant-feeding period, which is entirely absent after entry into the ant nest. In these species, the last instar larvae are equipped with a special gland on the dorsum of the 10th segment, from which is secreted a clear, liquid substance that is attractive to ants.
The 3rd instar larvae of L. arion do not evacuate the hindgut until right before pupation, which differs from the normal in Lepidoptera, but resembles Hymenoptera. Clark (1926) examined the excrement to find many dermal hairs and mandibles of Myrmica, thus establishing predation. Pupation occurs in springtime in situ only on thyme, and it is only in the 4th stage that the larvae enter the nests of Myrmica. The life cycle takes one year of which 10 months represents the larval period. All of this, with the exception of the first 2 weeks, is in an ant nest.
Larvae in the subfamily Gerydinae feed entirely on other insects, particularly Homoptera. Gerydus chinensis Feld. is found most often among aphids, and the larvae are thought to consume ca. 20 individuals per day (Kershaw 1905). The prey are often seized with the forelegs and held in the air while being consumed. The eggs are laid directly among the aphids and the ants who attend them, and the female sometimes even thrusts them aside with her ovipositor during oviposition. Megalopalpus zymna D. & H. (Lamborn 1914) differs in that it is associated intimately with ants of the genus Pheidole during development. However, the larvae's food, nymphs of Cicadellidae and Membracidae, is enclosed within the ant shelters. The female butterfly lays her eggs singly in the area of such shelters as contain the proper hosts. Sometimes she may place them directly on an egg mass or on the host body. The act of attacking a host reveals an interesting adaptation whereby capture is readily accomplished. The larva approaches the host with its legs raised and vibrating and causes them to caress the wings of the latter, thus stimulating the ministrations given by the ants with their antennae (Clausen 1940). Finally the head attains a position directly over the body, after which the prey is seized between the legs and feeding occurs at a point just behind the head. The prey may ultimately also be raised into the air. Both nymphs and adults are attacked, although the former are more common. The larva of Megalopalpus is protected by a hard integument which is studded with tubercles surmounted by coarse hairs. The ants derive no benefit from their presence in the shelter and thus are not attentive. The adult butterflies have the habit of feeding on the body secretions of the same hosts, rather than on nectar and honeydew. They probe the body with the proboscis and apparently derive some nutritional value from the secretions. They have also been found to do likewise on the plant surface on which the hosts rest (Clausen 1940/62).
Numerous modification in the predaceous mode of life are shown by species of Liphyrinae. Liphyra brassolis F. caterpillars feed on the larvae of the green tree ant, Oecophylla smargdina F. in Australia (Dodd 1902). The eggs are usually laid in pairs on the branches or trunks of trees containing ant colonies, and the young larvae make their way into the nest. They seem to move from nest to nest while feeding, and pupation occurs in the host nest. The last larval skin is not discarded but remains in changed form as an outer covering for the pupa. The adult moths are covered with many loose scales that seem held together by an oily substance. This covering is thought to serve as a protection from the very aggressive host ants, especially during moth emergence.
Euliphyra mirifica Holl., which is found in Oecophylla in Africa, does not appear to be predaceous, but rather the larvae are fed by the ants. The species of the genus Aslauga are predaceous on Coccidae, especially the soft scales and mealybugs. The larvae have a hard integument, covered with tubercles, which provides protection from ants attending their hosts. This genus was thought to have arisen from lichen-feeding ancestors, and the change to the coccid-feeding habit has occurred gradually (Balduf 1938). It was believed that first the coccids were associated among the lichens and consumed indiscriminately. Then, during times when lichen growth was prevented by adverse conditions, the larvae were confronted with a choice between starvation and feeding on Coccidae.