Lycaenid Butterflies and Ants: Selection for Enemy-Free Space

Many lycaenid butterflies counter attacks from natural enemies by associating with protective ants. The acquisition of this enemy-free space has strongly influenced lycaenid evolution. Four major adaptations are discussed: the thick larval cuticle, appeasement pheromones, the nectar gland with associated tentacles, and location of ants by ovipositing adults. The larval nectary is hypothesized to have a sequestering function when ants and larval food are not immediately coincident, and to release sheltering behavior by ants that reduces larval and pupal apparency. In facultative ant relationships the nectary may also function to appease "unknown" ants. When ants and larval food are coincident, the nectary is often absent or nonfunctional. Lycaenid larvae eat a diversity of unrelated foods, including flowering plants, fungi, lichens, cycads, ferns, conifers, homopterans, and ant larvae. They also "milk" homopterans and are fed orally by ants. These dietary shifts are apparently strongly conditioned by the dependence of the butterfly's eggs, larvae, and pupae upon ant protection. I suggest that unapparent larval foods (those that are ephemeral and difficult to find) and unpredictable ant resources select against ant specialization, permitting only opportunistic use of protective ants. Conversely, butterflies interacting with apparent plant and ant resources are hypothesized to become increasingly ant specialized, resulting in enemy-escape mechanisms that are highly dependent upon the distribution and abundances of specific ant species or their congeners. Radical dietary shifts are suggested to result from female predisposition to oviposit in response to particular ants, which may often be discovered on new hosts.