Introduction: extinctions and conservation need

Vast numbers of insect species exist on Earth. They are the predominant components of animal species richness in most terrestrial and freshwater environments. and by far outnumber many more familiar or popular animal groups, such as vertebrates. Estimates of the numbers of living insect species range up to several tens of millions; no one knows how many, but biologists accept easily estimates within the range of 5–10 million species as realistic. However, only about a million insect species have been formally described and named. The very levels of uncertainty over numbers of existing insect species are sobering reminders of what we do not know of our natural world. They help to emphasise our general ignorance over the diversity and ecological roles of many of the organisms that drive and maintain the ecological processes that sustain natural communities.

There is little doubt that very many insects have declined over the past century or so in response to human activities in many parts of the world. Such losses, reflecting changes we have made to their habitats and the resources on which they depend, have been documented most fully (but still with many substantial gaps in knowledge) in some temperate regions of the world (Stewart & New 2007). Insect extinctions and declines may be considerably greater in much of the tropics (Lewis & Basset 2007), where they are less heralded, but where numbers of insect species appear to be vastly higher than in many temperate regions.