Size is perhaps the most conspicuous feature of an organism, and has profound effects on nearly every aspect of organismal design, behavior, and function (Peters 1983, Schmidt-Nielsen 1984, Brown & West 2000, Dial et al. 2008). Across the tree of life, organisms span an impressive 21 orders of magnitude in size, ranging from mycoplasmas (10−13 g) to blue whales (108 g) (Schimidt-Nielsen 1984). In particular, Orthoptera (crickets, katydids, locusts, grasshoppers and wetas) and Phasmatodea (walkingsticks) display some of the most striking variation in size among terrestrial animals, from tiny 2-mm long ant-crickets to giant 357-mm long Malaysian walkingsticks (Otte & Alexander 1983; Wetterer & Hugel 2008; Natural History Museum, London). As evinced by the impressive array of subjects in this special issue on “Body size in Orthoptera”, orthopterans are model organisms in which to study the ecological and evolutionary significance of size.
At present count, there are ~ 24,300 known orthopteran species and ~ 3,500 known phasmatids (Orthoptera Species File, Phasmida Species File), with many more species likely to be unearthed with the continued progression of molecular phylogenetic studies in coming years. Thus far, phylogenetic studies generally support a monophyletic hypothesis for the Orthoptera (Gorochov 1995, Storozhenko 1997, Flook et al. 1999), although much work using modern molecular and statistical approaches remains to be done to resolve the higher-level relationships. The first known orthopteran fossil dates back to the upper Carboniferous period (~ 299 mya, Chopard 1920, Storozhenko 1997, Gorochov 2001), making orthopterans one of the most ancient of insect lineages. And recently, an entirely new order of orthopteroid-like insects, the Mantophasmatodea, was discovered (Klass et al. 2002, Terry & Whiting 2005), suggesting we still have much to learn about this diverse group. These remarkable animals also inhabit virtually every terrestrial biome type, where they are often highly abundant, sometimes spectacularly so, with up to 30,000 individuals per square meter in the case of locust hoppers (Uvarov 1977). Because of their high densities, orthopterans frequently play critical roles in terrestrial food webs as both herbivores (Schmitz 2005) and prey (see Whitman & Vincent 2008), and cause serious economic damage to crops and rangeland (Metcalf et al. 1962, Joern & Gaines 1990, Krall 1994). Understanding the adaptive nature of size variation in this diverse group of insects may not only shed significant light on a number of unresolved issues in ecological and evolutionary biology, but has practical value as well in pest management.
This special issue of JOR on “Body size in Orthoptera”, brings together a diverse array of 32 articles with this lofty goal in mind. The papers explore the full range of size-related topics, from understanding environmental and genetic control of size, to its geographic and sexual expression, to its fitness consequences and evolution, to its role in the conservation of endangered Orthoptera. It addresses how body size is influenced by nearly every aspect of the environment, and in turn influences nearly every conceivable aspect of orthopteran biology, from morphology and physiology to feeding, dispersal, defense, to mating, fecundity, and life-history strategies, and ultimately to fitness itself. We hope that the wide-reaching nature of these papers will help to guide the various avenues of research being explored on size in the Orthoptera, and to integrate these disparate topics into a more cohesive whole.