PRIMER: BIOLOGY OF COCKROACHES
The most common and most important household pests are cockroaches. Most common because they occur around the world; most important because they can carry and spread numerous disease organisms. Cockroaches are known to carry four strains of poliomyelitis, more than 40 different pathogenic bacteria, and the eggs of several pathogenic worms. It has been estimated that a single cockroach can carry a total of 13,470 bacteria. Although there are more than 3500 different species of cockroaches, only about 10 species are regularly associated with the household environment.
The three most common species are the German cockroach, American cockroach, and oriental cockroach. Female cockroaches do not lay eggs one at a time; instead they produce small egg cases that contain from 6 to 40 eggs. This egg case is deposited in locations that will provide adequate food and water for the developing immatures. Young cockroaches (called nymphs) begin feeding soon after they hatch from the egg case. They feed on the same materials as the adults, and look like adults except for size and absence of wings. After shedding their skins several times to grow larger, they become winged adults. Adult cockroaches live for a few months to over a year, depending on the species. They mate several times, and the females generally produce one egg case per month. The mouthparts of cockroaches are the biting-and-chewing type. These insects can feed on a variety of foods, but they seem to prefer starchy and sugary materials. They will feed on milk, cheese, meats, pastry, flour, meal, grease, chocolate, and a variety of other foods. They can feed just as freely on dead insects, other cockroaches, and human waste. They usually feed at night when they are not likely to be disturbed by human activities, but when infestations are heavy and widespread they can be seen foraging during the day.
German cockroach, Blattella germanica.
This is the most common and widespread household cockroach. It is a small insect, about 3/4" long, and is yellowish brown with two dark brown stripes behind the head. Both male and female have well-developed wings, but they do not fly. Adult German cockroaches are most common in areas of the house in which there is abundant food, water, and harborage. These areas include the kitchen and bathroom, but may also include other rooms when there is poor sanitation or there is a large infestation and available harborages in the kitchen and bathroom are limited.
German cockroaches forage for food primarily at night, and remain relatively inactive during the day. Adults and large nymphs move out of cracks and crevices and search for food and water for several hours each night, small nymphs may remain within harborages and forage for food scraps there. The males are the most active, the females are active when they are not carrying an egg case. While females are producing a carrying an egg case they are inactive, eating and drinking infrequently.
German cockroaches have small brown egg cases which contain from 30 to 40 eggs. The female carries the egg case protruding from the tip of her abdomen until about 24 hours before it hatches. She then places the egg case in an area where there is abundant food, water, and harborage. The adult female may live for about 6 months and produce an egg case a month for a total of about 240 nymphs.
American cockroach, Periplaneta americana.
This is the largest cockroach in the United States and it is distributed nearly throughout the country. Adults may reach a length of 2". The color of adult cockroaches is brown, the young are pale brown. In southern regions of the country this species is both an indoor and outdoor pest. Indoors it may be associated with kitchens and bathrooms, and outdoors it is usually found in leaf litter around the house and flower beds. In northern regions of the country this species is primarily an indoor pest which moves outdoors during the warm months. It most often infests cool basement areas, sewer systems, and warehouse environments. From basements and sewer systems it may move into the living space, but usually not in large numbers. Although it moves primarily by running, this species of cockroach can fly for short distances, especially during warm weather.
The female American cockroach deposits her egg case as soon as it is produced. The adult female may live for 12 to 18 months and lay as many as 33 egg cases. The females often deposit their egg cases in protected places and may cover them with pieces of organic matter. The nymphs feed on the same material as the adults, and may take nearly 12 month to complete their development. The adults and nymphs actively forage during the warm months of the year, and are inactive during the winter even in relatively warm climates.
Other Cockroach Species
Periplaneta species of cockroaches are also household pests. These species include the smokybrown cockroach, Periplaneta fuliginosa, and the brown cockroach, P. brunnea. The biology and habits of these species is similar to the American cockroach, but their distribution is limited. The brown and smokybrown cockroach are found primarily associated with houses and other structures in the southern region and less often in areas with cold winters.
Oriental cockroach, Blatta orientalis. This cockroach is about 1" long and is dark brown to black in color. The wings are very short in the male and do not reach to the tip of the abdomen, the wings are reduced to short pads in the female. The nymphs are pale brown in color. This cockroach is widely distributed in the United States, but is more common in northern regions. It is tolerant of cool conditions and is often active in the early spring when the weather is still cool. In the household environment this species often infests basement areas, or the perimeter of buildings. It is active during the spring and summer, but forages little if any during the winter. Development. The female deposits her egg case soon after it is formed. Each female can produce one egg case per month for the 5-6 months of her life. The nymphs develop slowly during the spring and summer and become nearly full grown by fall. Large nymphs overwinter with little feeding and molt to the adult stage in the spring. Adults live for a few months, but most are dead in the population by fall.