THE MAGNITUDE OF GLOBAL INSECT SPECIES RICHNESS

Recent suggestions that insects number tens of millions of species have received much attention. Little consideration, however, has been given to how such estimates compare with what else we know about insect species richness. Perhaps most significantly, the specialist knowledge of the taxonomic community at large has generally been ignored. Collation of published and unpublished information from this source provides little to encourage belief in truly vast numbers of undescribed species of insects. For the insect groups for which figures are available, estimates of global total numbers of species are typically less than ten times the numbers of described species. Although minimum global estimates are more readily constructed than upper estimates, these figures uniformly fail to support assertions that there are 30 million or more species of insects. Rather, a figure of less than ten million seems more tenable, and one of around five million feasible. Additional, more circumstantial, evidence tends to support the idea that insect species numbers may not be as vast as has been claimed. First, the contribution of canopy specialists to global richness may be less than often suggested. Second, a higher proportion of species than commonly entertained may have moderate to large geographic ranges. Third, the number of groups failing to increase in richness in the tropics may have been underestimated. Finally, the proportion of undescribed species encountered by many taxonomists seems insufficient to justify estimates of vast species numbers.