Towards an integrative approach to understanding collective behaviour in caterpillars.

To evolve, and remain adaptive, collective behaviours must have a positive impact on overall individual fitness. However, these adaptive benefits may not be immediately apparent owing to an array of interactions with other ecological traits, which can depend on a lineage's evolutionary past and the mechanisms controlling group behaviour. A coherent understanding of how these behaviours evolve, are exhibited, and are coordinated across individuals, therefore requires an integrative approach spanning traditional disciplines in behavioural biology. Here, we argue that lepidopteran larvae are well placed to serve as study systems for investigating the integrative biology of collective behaviour. Lepidopteran larvae display a striking diversity in social behaviour, which illustrates critical interactions between ecological, morphological and behavioural traits. While previous, often classic, work has provided an understanding of how and why collective behaviours evolve in Lepidoptera, much less is known about the developmental and mechanistic basis of these traits. Recent advances in the quantification of behaviour, and the availability of genomic resources and manipulative tools, allied with the exploitation of the behavioural diversity of tractable lepidopteran clades, will change this. In doing so, we will be able to address previously intractable questions that can reveal the interplay between levels of biological variation. This article is part of a discussion meeting issue 'Collective behaviour through time'.