Cockroaches are an enormously ancient and successful group of insects. The roaches were one of the very first terrestrial insects, appearing during the early Carboniferous era some 280 million years ago. Conditions on earth back then were warm, humid and damp, and the land was covered with a rich profusion of plants. These, of course, are perfect conditions for cockroaches, and the blattids far outnumbered all of the other insect groups living at the time, leading some paleontologists to refer to the Carboniferous period as the "Age of Cockroaches". Since that time they have hardly changed at all, and fossil specimens of the 260 million year old roach species Mylacris can scarcely be distinguished from living species. Some of the cockroaches found in the Pennsylvanian period (the latter half of the Carboniferous) were over six inches long. The wings on these early roaches were much larger, proportionately, than in modern species. The Pennsylvanian roaches also did not have the first pair of wings hardened and stiffened for protection, but instead used both pairs of wings for flight.
Some of the earliest cockroach ancestors, the Paleodictyoptera, had two pairs of wings on the second and third thoracic segments, but also a pair of partial flaplike half-wings on the first thoracic segment. It has been speculated that the original insect wings may have evolved from such flaplike extensions of the exoskeleton.
The insects were the first group of organisms to evolve powered flight. The earliest flying insects, dragonflies and mayflies, have two pairs of wings that stick straight out to the sides when the organism is at rest. More advanced insects, called Neoptera, have wings that can be folded back along the body when not in use. In some of these, like the cockroaches and beetles, the first pair of wings has been modified to form a hard protective cover for the flight wings.
The hissing cockroaches have no wings and have lost their ability to fly. Even those roaches that still have functional wings, like the death’s head roaches and the American cockroach, are clumsy fliers that buzz along awkwardly for short distances. It may be that, with further evolution, all of the roaches will completely lose their ability to fly, and will depend solely on their superb running ability to escape predators.
Roaches are closely related to several groups of living insects. It is believed that the termites diverged from the cockroaches about 70 million years ago. Some of the more primitive wood-eating cockroaches, such as Cryptocercus punctulatus, have microorganisms in their intestines that break down the cellulose in wood and convert it to sugars that the roach can digest. This is the same arrangement used by termites, and many of the microorganisms in termite intestines are closely related to those found in roaches, indicating that they share an evolutionary relationship.
The preying mantis family, which shares a number of anatomical characteristics with the roaches, diverged from the cockroach group even more recently. Some of the traits which mantids share with the cockroaches are an incomplete metamorphosis life cycle, in which the newly emerged young do not pass through a larval or pupal stage but look like smaller wingless versions of their parents; the presence of cerci or sensory hairs at the rear of the abdomen; and the production of eggs in an ootheca by the female.
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