7.1.2. Taxonomy and classification
Difficulties with attaining a comprehensive, coherent classification of the insects arise when phylogeny is obscured by complex evolutionary diversifications. These include radiations associated with adoption of specialized plant or animal feeding (phytophagy and parasitism; section 8.6) and radiations from a single founder on isolated islands (section 8.7). Difficulties arise also because of conflicting evidence from immature and adult insects, but, above all, they derive from the immense number of species (section 1.3.2).
Scientists who study the taxonomy of insects — i.e. describe, name, and classify them — face a daunting task. Virtually all the world’s vertebrates are described, their past and present distributions verified and their behaviors and ecologies studied at some level. In contrast, perhaps only 5–20% of the estimated number of insect species have been described formally, let alone studied biologically. The disproportionate allocation of taxonomic resources is exemplified by Q.D. Wheeler’s report for the USA of seven described mammal species per mammal taxonomist in contrast to 425 described insects per insect taxonomist. These ratios, which probably have worldwide application, become even more alarming if we include estimates of undescribed species. There are very few unnamed mammals, but estimates of global insect diversity may involve millions of undescribed species.
Despite these problems, we are moving towards a consensus view on many of the internal relationships of Insecta and their wider grouping, the Hexapoda. These are discussed below.