The order Coleoptera is divided into four suborders: Archostemata, considered the most primitive; Ade-phaga, named for its carnivorous members; Myxophaga, which are algae-eaters; and Polyphaga, the largest suborder, encompassing 90% of beetle families, in which species with diverse feeding habits are grouped. The number of beetle families varies between 135 and 170, depending on whether family designations are based on larval or adult morphology (Crowson 1981, Lawrence and Newton 1995, Downie and Arnett 1996). About 112 families include species that occur in North America.

More than 300,000 species of beetles have been described, representing 30-40% of all known insects. About 25,000 species of beetles occur in the United States and Canada (White 1983, Arnett 1990). Fewer than 100 species worldwide are known to be of public health or veterinary importance. Most of these are in the suborder Polyphaga. The species that have the greatest impact on the health of human and domestic animals are in the following families: Meloidae (blister beetles), Oedemeridae (false blister beetles), Staphylinidae (rove beetles), Tenebrionidae (darkling beetles), Dermesti-dae (larder beetles), and Scarabaeidae (scarab or dung beetles).

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elytra so that the abdominal tergites are visible dorsally (e.g., rove beetles and some blister beetles). Most beetles have eight visible abdominal tergites which can be seen when the elytra and hind wings are raised.

Defensive ┬┐lands that secrete substances to repel predators are best developed in beetles in the suborder Ade-phaga. They are generally present as pygidialglands that open dorsally near the end of the abdomen. Secretions from these glands in the Adephaga are not known to cause notable ill effects in mammals. Within the Polyphaga, py-gidial glands occur in a few families, such as the Tene-brionidae. In tenebrionids, the pygidial glands produce secretions that can deter small mammals and cause human skin irritation. The pygidial secretions of most other polyphagan species are not known to affect vertebrates.

Beetles that contain chemicals that are especially irritating to humans and other animals have toxic substances dispersed throughout their bodies rather than sequestered in specialized glands. The blister beetles, paederine rove beetles, and lady beetles fall within this group.

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