Geographical Distribution of the Dermaptera and the Continental Drift Hypothesis

Abstract

THE Dermaptera (earwigs) are a group of insects which live in litter, under bark, in soil, compact vegetation, hollow plant stems and have retiring habits. Many of the primitive subfamilies are wingless, and only a few of the winged species are known to fly. Popham and Brindle^1,2 have given details of the geographical distribution of each species. The Dermaptera seem to have undergone speciation as a result of local geographical barriers, so that most species have limited distributions; a handful of species have become cosmopolitan, largely as a result of human influence, but we have ignored these in this investigation. Popham and Brindle's records¹ show that all the less specialized Dermapteran subfamilies have a circumtropical distribution while only the more specialized subfamilies such as the Labiinae, Anechurinae and Forficulinae are abundant in the northern hemisphere. There are two possible explanations for this distribution: either the Dermaptera evolved in the northern hemisphere and subsequently spread into the southern continents, or the earwigs were evolving throughout the proto-continent of Gondwanaland as it disintegrated during the late Jurassic and early Cretaceous, possibly as suggested by Lester King³. If the first explanation is correct, there should be a greater similarity between the Dermapteran faunas of North and South America, Eurasia and Africa and between Eurasia and the Oriental Region, than between the faunas of the southern continents. On the other hand, if continental drift has been the major factor responsible for the distribution of the Dermaptera, there should be greater similarity between the faunas of the southern hemisphere than between those of the northern and southern hemispheres.