Insects are the most diverse group in the animal kingdom, with close to a million named and described species and countless species yet to be discovered. Insects have not been nearly as thoroughly studied as the vertebrate groups, and so there are likely to be many endangered insects whose desperate state remains unrealized. In 2004 there were 39 endangered insects (35 U.S., four foreign) and nine threatened insects (all U.S.) listed with the U.S. Fish and Wildlife Service under the Endangered Species Act. There are also 12 endangered arachnids (all U.S. species), a group related to insects that includes spiders, ticks, and mites. Listed U.S. threatened and endangered insects and spiders are shown in Table 9.1.

There are also 553 threatened insect species and ten threatened arachnids listed in the 2003 IUCN Red List of Threatened Species from the World Conservation Union. Most of...