The adult German cockroach is 10 to 15mm long. The Common or Oriental cockroach is 20 to 24mm long. They are rarely able to survive out of doors in the British climate, but thrive around the heating ducts and boiler rooms of large centrally heated buildings e.g. hospitals, bakeries, hotel and restaurant kitchens, laundries and blocks of flats. They cluster around pipes, stoves, and sinks, especially in humid areas.
The German cockroach carries its egg case, a small brown purse-like capsule, until the 30 or more nymphs are ready to hatch from it. The Oriental cockroach deposits its 13mm long egg capsule on packaging, sacking or in suitable dark crevices before the 16 or 18 nymphs hatch out.
Cockroaches grow in stages - from nymphs to maturity in six to 12 months for the Oriental cockroach, but only in as many weeks in the case of the German cockroach.
Both species eat any sort of food and are most active after dark, from their inaccessible harbourages, to forage, contaminating food and food utensils, or food preparation surfaces as they go. They taint food with an obnoxious smell and may be carriers of various diseases, including serious food poisoning.
Based on fossil records, cockroaches have remained little changed for 200 million years.There are over 4000 different species of cockroaches worldwide not all are regarded as pests. Those species, which are now classed as pests originated in tropical climates but have now become cosmopolitan in temperate zones, having been distributed by commercial activities.
Common cockroach species
The cockroach species commonly found in the UK are:
Oriental cockroach (Blattaorientalis) Males are approximately 25mm long, females approximately 32mm long; shiny and very dark brown, nearly black in appearance, nymphs (immatures) may be reddish brown; they are poor climbers on smooth surfaces, which may limit their distribution within a building; they appear to be cold tolerant in that they are often found outside buildings, in drains, gardens, sewers, external brickwork etc, a factor which should be remembered when controlling them.
German cockroach (Blattellagermanica)
Adult size 13-16mm; the adult is light brown incolour with two dark almost parallel longitudinal stripes on their pronotal shield; they are found throughout buildings but show a preference for warm humid areas; they are good climbers, being able to climb vertical glass or tiled surfaces; an infestation of these cockroaches can be quickly established once they have entered any premises.
Brown-banded cockroach (Supellalongipalpa) Adult size 11-15mm; this cockroach is small, light brown in colour and is often mistaken for the German cockroach; this cockroach needs hot conditions to survive, it prefers 27°C and over but it is becoming more common as a pest in the UK; it is typically found in light switches, electrical appliances, motor housings, etc.
American cockroach (Periplanetaamericana) Adult size 34-53mm; the adult is is reddish brown in colour and is fully winged. Male wings extend beyond the tip of the abdomen; female wings do not. There is a pale brown to yellowish band around the edges of the pronotum. This species is not well established in Britain. It is not as cold tolerant as Blattaorientalis andBlattellagermanica. Typical infestations in the United Kingdom are port areas, where it is introduced via ships. Sites infested include food premises, greenhouses, zoos, large centrally heated humid environments, etc.
Egg case (oothecae) development in cockroaches
General biology and behaviour
Cockroaches are omnivorous. In addition to conventional foodstuffs, they will feed on a wide range of organic matter including other cockroaches. Their activity peaks during hours of darkness.
They exhibit incomplete metamorphosis; the juvenile stages or nymphs resemble the adults. Each cockroach moults several times in its life cycle producing a larger nymph and eventually moulting to the adult stage. Some species are fully winged in the adults, others may have reduced wings or wing buds. When wings are present, they are leathery and veined. The females of those cockroaches classed as pests all produce egg cases or oothecae, which contain eggs, which hatch inside the case from whichnymphal cockroaches emerge. During the daytime, cockroaches spend most of their time in harbourages grouped together. This behaviour is influenced by them finding the same suitable harbourage. They also produce an aggregation pheromone, which is a chemical messenger to other cockroaches of the same species, who respond by being attracted to the source of the pheromone. As this pheromone is present in cockroach faeces, cockroaches will also be attracted to areas previously contaminated by cockroaches.The development of cockroaches is affected by food quality, humidity, temperature, and day length.
Food contamination problem
Cockroaches foul their environment with faeces, regurgitated food and they taint materials with their characteristic smell. The air in infested premises may contain fragments of their exoskeletons and cockroach excrement. Cockroaches also contaminate food directly as they move from filth to food indiscriminately and are therefore implicated in the mechanical transmission of many pathogens, such as those causing food poisoning and wound infections.Because residual allergens can remain as active contaminants for some time following a treatment, a thorough cleaning regime should be carried out afterwards.
Cockroach biology and life cycle
Cockroaches undergo egg and nymphal stages before becoming adults. Eggs produced by female cockroaches are enclosed in resilient egg cases known as oothecae. The oothecae of cockroach species contain a range of nymph numbers which is dependent on species. The time it takes for eggs to hatch into nymphs varies between species as well and depends upon environmental conditions. Nymphs free themselves from the oothecae by working in concert.
Nymphs resemble adults in appearance and behavior, although they are smaller in size and do not have wings. Nymphs undergo a series of molts before becoming fully mature adults. After the final molt, nymphs of some cockroaches are equipped with wings.
After nymphs molt, they are pale in color. Nymphal cockroaches that have recently molted are often misidentified as albino roaches. Within a few hours, they will darken to the proper color. Adult cockroaches have an average lifespan of around a year but it depends on species. Temperature and other environmental conditions greatly affect the survival of cockroaches. Adult cockroaches reproduce rapidly and are known scavengers. Cockroaches usually are nocturnal. Roaches that are active during the day may be victims of overcrowding or may be looking for food or water.
Eliminate the roaches’ food and water supply. Place all food in sealed containers. Place all garbage in sealed cans. Empty trash cans inside of the home at least once a day, more if food scraps are inside. Fix leaky faucets or pipes. Regularly cleaning Scrupulous hygiene and prompt disposal of all refuse will discourage flies. Windows may be fitted with fly screens. Food should be kept covered. Dustbins should be sited away from doors and windows, have tight-fitting lids and be sprayed or dusted inside and beneath with a household insecticide in warm weather.