An international team of scientists, which involves Gerard Talavera, a researcher at the Institute of Evolutionary Biology (IBE), a joint CSIC-UPF centre, has studied the Miletinae butterfly subfamily, which are special in that they do not feed on plants, as do most Lepidoptera. The results of the study are published in the journal Evolution this January. 

In this work, the scientists have solved the phylogeny of the Miletinae, which they have used as a basis for studying the evolution of aphytophagy in butterflies, changes in dietary preference, and interactions established by the carnivorous caterpillars with their hosts (ants) and prey (hemiptera).

When you think of butterflies it is difficult to associate them with cruel carnivorous species that prey on other animals. Lepidoptera are one of the most diverse of the four orders of insects, and in fact are mostly phytophages, meaning they feed on plants.

But a small proportion of species, less than 1% (between 200 and 300 species), are aphytophages, meaning they feed on nutrients other than from living plants.

Some aphytophagous butterflies are predators that feed on other animals, mainly insects. Others are parasites, taking advantage while reducing the viability of their host without killing it, and some can even eat detritus, lichens or extrafloral nectar.

A group of exceptional butterflies

Lineages that have become mutualistic, or that have mutually beneficial relationships for both parties, seem to persist and diversify in nature much more than parasitism. That is, evolution would tend towards favouring cooperation. The Miletinae, parasites and carnivores, will remain a remarkable exception from this pattern.

During the evolution of the Lepidoptera few aphytophagous lineages have persisted and diversified. However, the Miletinae subfamily of Lycaenidae is an exception and has become the largest radiation of aphytophagous butterflies, with some 140 species.

The larvae of most members of the Miletinae prey on hemiptera, to which they get access by parasiting the ants that tend to them.

In addition, the study published in Evolution examines the biogeographical history of the group and introduces the discussion as to what have been the causes and effects of the drastic dietary changes among the different species of the food chain.

The benefit for both parties predominates in nature

The example of the Miletinae describes another case of how complex the networks of interactions between species that some insects have developed can be. As Talavera explains, "part of the research we are conducting focuses on researching what are the costs and benefits of association, the possible factors that could promote the evolution of specialization towards mutualistic interactions, and whether the choice of cooperation has promoted the diversification of species".

Interestingly, this type of interactions has been inspiring scholars of game theory applied to the economy for some time, that is to say, the study of the strategies in taking decisions that maximize gains or returns.  

Reference work:

Zofia A. Kaliszewska, David J. Lohman, Kathrin Sommer, Glenn Adelson, Douglas B. Rand, John Mathew,  Gerard Talavera and Naomi E. Pierce (2015),  " When caterpillars attack: biogeography and life history evolution of the  Miletinae (Lepidoptera: Lycaenidae) ", Evolution. DOI: 10.1111/evo.12599.

Further information:

The BBC has given coverage to this work at: Melissa Hogenboom (2015),  Earth, " Carnivorous caterpillars attack victims"