Social insects and arachnids exhibit forms of complex behavior that involve cooperation in building a nest, defending against attackers or rearing offspring. This book is a comprehensive, up-to-date guide to sociality and its evolution in a wide range of taxa. In it, leading researchers review the extent of sociality in different insect and arachnid groups, analyze the genetic, ecological and demographic causes of sociality from a comparative perspective, and suggest ways in which the field can be better understood. The book contains fascinating accounts of the social lives of many different insects and arachnids, as well as tests of current theories of the evolution of social behavior. The Evolution of Social Behaviour in Insects and Arachnids provides essential reading and insight for students and researchers interested in social behavior, behavioral ecology, entomology, and arachnology.