Trogidae, sometimes called hide beetles, is a family of beetles with a distinctive warty or bumpy appearance. Found worldwide, the family includes about 300 species contained in four or five genera. Trogids range in length from 2 to 20 mm. Their shape is oblong to oval, with a generally flat abdomen. Their color ranges from brown to gray or black, and they often encrust their bodies with soil. They resemble scarab beetles with heavy limbs and spurs. They are scavengers and are among the last species to visit and feed on carrion. They are most often found on the dry remains of dead animals. Both adults and larvae eat feathers and skin. Some species are found in bird and mammal nests. Details of the life histories of many species are poorly known, since many are specialized to particular types of nests. They are often overlooked by predators and collectors due to their behaviors of covering their bodies with soil and becoming motionless when disturbed. This group may also be considered Troginae, a subfamily of the Scarabaeidae. The common name "skin beetle" is sometimes used in reference to these beetles, but more often refers to species of the Dermestidae. Origins Hide beetles are found worldwide. More species of Trogidae are found in dry environments instead of moist environments, typically temperate plains areas. Each genus is more diverse in different regions of the world. Trox is found in the Holarctic/Ethiopian area, Omorgus within the southern continents, and Polynoncus is found in South America. Controversy exists over whether Trogidae is a family of its own or a subfamily of Scarabaeidae. One major reason for the dispute between classifications is the possible evolution of the ommatidium in the eyes. Different environmental pressures and predators may have led to the adaptation of ommatidium structures within this family. For example, the more advanced and numerous the ommatidium, the more present the larger the ability of the insect to escape and elude predators. The Trogidae may have evolved in Australia. The oldest known fossils are from the Early Cretaceous (Aptian) Zaza Formation of Russia and the Shar-Tolgoy and Dzun-Bain Formations of Mongolia, assignable to the extant genus Trox as well as the extinct genera Cretomorgus and Paratrox. Other known fossils include Kresnikus beynoni found in mid-Cretaceous aged Burmese amber. Anatomy Trogidae are characterized by their distinct soil-encrusted, warty, or bumpy appearance. They are usually brown, gray, or