Cockroaches are insects in the order Blattaria. They are somewhat flat, oval shaped, leathery in texture, and are usually brown or black in color. Cockroaches range in body size from 0.1 to 2.3 in (2.5 to 60 mm), and are rampant pest insects in human inhabited areas, as well as common outdoor insects in most warm areas of the world.
These insects were formerly classified in the order Orthoptera, which consists of the grasshoppers and katydids. Now they are often classified along with the mantises in an order referred to as Dictyoptera. The separate order Blattaria, however, is the more common classification for them, and this order is placed in the phylogeny, or evolutionary history, of the class Insecta between the orders Mantodea, the mantids, and Isoptera, the termites.
The primitive wood-boring cockroaches in the family Cryptocercidae, a family in which there is only a single species in the United States, Cryptocercus punctulatus, are thought to have shared a common ancestor with termites. The evidence for this is a close phylogenetic relationship between the two groups' obligate intestinal symbionts, single-celled organisms called protozoans which break down the wood that the insects eat into a form that is useful to the insect, and in turn receive nutrition from the matter which is not nutritive to the insect. There are also behavioral similarities between these wood-boring cockroaches and termites, including the fact that they both live gregariously in family groups, a characteristic not shared by any of the other types of cockroaches. Finally, the relationship between the two orders is evidenced by the resemblance between Cryptocercus nymphs, and adult termites.
Interesting morphological characteristics of these insects are their chewing mouthparts and large compound eye. The pronotum, or segment of the thorax that is closest to the head, conceals the head, and in most species, both male and female are winged, although they rarely fly. They exhibit many fascinating behaviors, such as the ability to stridulate, that is, produce sound by rubbing a comb-like structure with a scraper. Other species, however, communicate by producing sound by drumming the tip of their abdomen on a substrate. An important developmental feature of these insects is their paurometabolous life-history. Paurometabolism is a type of simple metamorphosis in which there are definite egg, immature or nymph, and adults stages, but no larval or pupal stages and in which the nymphs resemble the adults except in size, development of wings, and body proportions. Habitat requirements of nymphs and adults do not vary in paurometabolous insects, a fact which helps cockroaches to thrive under a rather generalized set of environmental conditions at all stages of their lives.
Cockroaches are saprophagous insects, or scavengers, feeding on a great variety of dead and decaying plant and animal matter such as leaf litter, rotting wood, and carrion, as well as live material. They are, thus, very flexible in their diet, and this flexibility allows them to exist under a wide range of conditions. In fact, the habitat types of this order span such areas as wood rat nests, grain storage silos, forest leaf litter, and nests of leaf cutter ants. They thrive in areas with moisture and warmth.
Cockroaches produce oothecae, sacs in which the eggs are held and protected by secretions produced by the female. These egg sacs may be carried by the female externally until the time of hatching, or internally until the female gives birth to live young, or they may simply be deposited on a suitable substrate and left to hatch without any care from the female.
Besides being rather fast runners, many cockroaches have other adaptations that allow them to escape from predation. One such defensive adaptation is the ability to produce an offensive odor which they emit when disturbed. Other species, such as the Madagascaran cockroach, Gromphadorhina laevigata, force air out through their spiracles, thus producing an intimidating hissing sound.
Cockroaches are worldwide in distribution, although most of this order's approximately 4,000 species occur in the tropics. In the United States and Canada, there are some 29 different genera, and about 50 species. Most of these species occur in the southern United States.
Due to their preference for moist, warm places, flexible diet, and nocturnal activity, cockroaches are very successful at living uncontrolled in human areas. Although annoying and often feared by people, they are not known to be significant disease carriers, crop pests, or agents of other large-scale damage to human areas. There are four species in North America which are common as household insects. They are the German cockroach (Blattella germanica), the American cockroach (Periplaneta americana), the brown-banded cockroach (Supella longipalpa), and the oriental cockroach (Blatta orientalis). The oothecae of these indoor species are often deposited on common household items such as cardboard boxes, and in this way may be transported from place to place before they actually hatch, thereby spreading to new areas.
In contrast to its image as a fearsome, although relatively harmless pest, the cockroach has for many years actually benefitted humans—a benefit that has resulted from its abundance and often large size. The cockroach has contributed greatly to our general understanding of physiology due to its use as a model study organism in biological research investigating nutrition, neurophysiology, and endocrinology. Medical knowledge has expanded as a result of the data gained from such studies of the cockroach.
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