Six species of cockroach, belonging to four genera, occur in Great Britain. They are Periplaneta Americana, P. australasiae, Blatta orientalis and Blatella germanica and two species of Ectobius. The latter are both endemic, but rare. The others have been brought in by trading ships, mainly in the seventeenth and eighteenth centuries: they are typically tropical and sub – tropical animals. In our colder climate they established themselves in buildings where they found the warmth they required. Thus they were formerly very common in warehouses, bakeries, boiler – houses, factories and private dwellings. There has been considerable diminution in their numbers in recent years, probably due to better standards of building, more hygienic food preparation and less scattering of food debris in buildings. Ectobius species are found in woods among litter.
Cockroaches are of ancient lineage. Insects very closely resembling them flourished in the Carboniferous period: there has been very little change throughout the vast periods of time that have elapsed since those early insects flourished. The species usually used for dissection is either the brown P. Americana or the smaller black B. orientalis. They differ little, apart from the fact that the female B. orientalis has vestigial wings and is incapable of flight. P. Americana is described here.
External Features of a Cockroach
The cockroach is an animal of about 40mm long and is colored a rich brown on the dorsal surface, though beneath the wings and on the ventral surface it is almost yellow. The body is clearly divisible into head, thorax and abdomen and is conspicuously flattened.
The head is small and when viewed from the front is almost pear-shaped: from the side it is much narrower. It is placed almost at right angles to the body, so that the mouth parts are ventral and the eyes dorsal. The sclerites covering the head are not always clearly separate. On top of the head and extending downward between the eyes and antennae are the two epicranial plates. Below them in front are successively the frons, clypeus and labrum. The latter forms the roof of the buccal cavity and is sometimes called the upper lip. At the sides are two cheek sclerites, the genae. The back of the head is joined to a flexible short neck region, and the floor of the bucca cavity is formed by the fused proximal portions of a pair of appendages. It is known as the labium. The large compound eyes are kidney – shaped, black in color, and are situated dorso – laterally. In front of them lie the long flexible antennae. The mouth parts are hinged at the sides there are three pairs: the mandibles, maxillae and two second maxillae partially fused to form the labium. The mandibles are strong, hard toothed structures, which do not bear palps. Immediately behind the mandibles are the maxillae, consisting of a protopodite of two podomeres, the cardo and stipes, a five – joined endopodite called a maxillary palp and an endite subdivided at its distal end into a claw – like lacinia and a hooded galea. The second maxillae have their three proximal pedometers fused to form the labium. They are known as the submentum, mentum and prementum: the latter bears a pair of endopodites known as labial palps and two endites having distally a glossa and paraglossa similar to the lacinia and galea of the first maxilla. The mandibles are used for chewing the food: the lacinia, galea, glossa and paraglossa assist in holding it and pushing it into the mouth, while the palps are olfactory in function. There are six segments of the crayfish is tabulated below.
Connecting the head to the thorax is a short neck. It is not a segmental region but an extended articular membrane supported by a few sclerotized patches known as the cervical sclerites.
Feeding Habits and Nutrition in Cockroach
The animals live in cracks and crevices of walls especially in the vicinity of fireplaces and boilers. They are nocturnal, emerging to feed only at night, when they devour a wide variety of organic materials. Cockroaches run very swiftly, but very rarely fly. The sexes are separate and there is a complicated copulatory process during which the male deposits a spermatophore near the female spermotheca. The female produces a purse – like ootheca containing sixteen eggs in two rows of eight. The young which emerge are almost small replicas of the adults except that they have no wings. It takes five years to complete development to maturity. Insects which pass through such a slight metamorphosis are described as heterometabolic and those in which the wings develop externally are placed in the division Exopterygota.