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Cockroach Biology

Cockroaches are very primitive insects. Their ancestors lived 200-350 million years ago in the Carboniferous Period, even before the dinosaurs. This geological period is sometimes called the "Age of Cockroaches" because they were so abundant. At this time, the climate on the earth was warm and moist, ideal conditions for them to thrive. Although climatic conditions are cooler and less humid now, present-day cockroach species are surprisingly similar to those preserved in fossils from the distant past.

Life Cycle, Behavior and Habitat

The cockroach is exceedingly hardy. It thrives on only crumbs and can survive long periods of time without food or water. Cockroaches often live in cracks and crevices so small that we can easily overlook them. Because they are such good survivors, it is essential to have a basic understanding of the cockroach life cycle, behavior and habitat before attempting any control tactic. Information about how long cockroaches live, and the number of eggs they produce is called their life cycle. All their habits or things they do during their entire life cycle can be thought of as behavior. The place where cockroaches live and eat is called their habitat. The life cycle, behavior and habitat of each cockroach species will be described in detail.

German Cockroach (Blattella germanica)

Life Cycle. The female German cockroach produces an egg case or capsule (the scientific term is ootheca) containing 30-40 eggs. After producing the egg case, the female carries it for about three weeks until the day the eggs hatch. She then goes into hiding before dropping her egg case. This behavior reduces possible harm to the female and her eggs. The immature German cockroaches (nymphs) grow fast. Nymphs that emerge from the egg cases will molt (shed their skins) six or seven times in about 60 days, and after the last molt, adult cockroaches emerge fully winged and sexually mature.

The female will produce four to eight egg cases in her lifetime. That can be over 300 offspring from a single female! After about 60 days, the nymphs that hatched from the first egg case will be mature adults ready to produce their own offspring. If half of these nymphs are females, and each of them produces 300 nymphs, and if half of those nymphs are females, and they each produce 300 nymphs.......... I think you begin to get the idea! From that original female German cockroach there could be more than 100,000 cockroaches in your home by the end of one year!

Behavior and Habitat. German cockroaches gather, or aggregate in dark places that have high humidity, contain paper, wood and other porous surfaces and have food readily available. They aggregate in these areas because the surfaces are "marked" with an aggregation pheromone, found in their feces. A pheromone is a chemical produced by one cockroach that affects the behavior of others. This aggregation pheromone is very attractive to the immature stages. The end result is that German cockroaches congregate in areas near porous surfaces that have little air movement, are dark and have large quantities of their own feces. Examples of these gathering places are in cracks and crevices around cabinets, wall and ceiling voids, in and around refrigerators, dishwashers, stoves, washers and dryers, and water heaters.

German cockroaches thrive in undisturbed, protected habitats that contain food and water. The most favorable humidity levels are found in kitchens and bathrooms under and around toilets, bathtubs, showers and sinks. They especially like sink traps, leaking faucets, standing water and wet sponges. German cockroaches will not leave these favorable areas unless they are forced out. If food, water and shelter (resources) are available, the cockroach population can multiply rapidly. When any of these resources are eliminated, populations can't grow and may even decline.

Inspections. Concentrating on undisturbed areas of high humidity (usually kitchens and bathrooms), inspections are done with flashlights looking for German cockroaches (alive or dead), fecal pellets (small, dried fecal particles) or fecal smears (feces is pressed or smeared onto surface), shed or cast off skins and empty egg cases. Traps should also be used to detect infestations and help estimate the size of the cockroach problem.

Brown-Banded Cockroach (Supella longipalpa)

Life Cycle. The egg case, containing 13-18 eggs, is usually glued to inconspicuous places in the habitat, such as on furniture, cabinets, behind picture frames, walls and ceilings. Egg cases hatch in about 50 days. In her lifetime (approximately six months) the female brown-banded cockroach can deposit as many as 14 egg cases. Nymphs molt six to eight times over a five- to six-month time span, before emerging as sexually mature winged adults. Male brown-banded cockroaches readily fly when disturbed.

A single brown-banded female cockroach has the potential to produce about 250 offspring. But, because of the longer time that it takes nymphs to grow into sexually mature adults, large populations are not produced as quickly as those of the German cockroach. In addition, because the egg cases are glued to objects in the environment soon after formation, they are susceptible to drying out, attack by fungi and other mortality factors which all contribute to produce a low hatch rate. This translates into a much lower potential for offspring production than for the German cockroach.

Behavior and Habitat. Brown-banded cockroaches build up their highest populations in high temperature areas. Because they require less water than German cockroaches, they often survive in drier locations that are unsuitable for German cockroaches. They frequently occur in locations at eye-level or above such as in cabinets, around closet shelves, behind pictures, in warm areas near motors of refrigerators, electric clocks, timers and television sets. Other favorite habitats are around the braces of kitchen chairs and tables, around objects on the wall and in shower stalls. Their egg cases can be found attached to rough surfaces like walls and textured ceilings but can also be found around the kitchen sink, desks, tables and other furniture.

Inspections. Inspections are similar to those for German cockroaches, but also look for fecal smears, cast skins, alive or dead individuals and egg cases glued to places in higher and drier areas that brown-banded cockroaches normally occupy. Because brown-banded cockroaches have such a long development and egg-hatching time, it is especially important that control efforts are monitored by inspections and trapping.

Oriental Cockroach (Blatta orientalis)

Life Cycle. A single female oriental cockroach has a much lower potential for producing offspring than either the German or the brown-banded females. The female oriental cockroach can produce up to eight egg cases in a season, but in areas where the winters are cold, like in Nebraska, fewer egg cases (as few as one per year) are produced. Since there are 16 eggs in a perfectly formed egg case, that number may be as low as 16.

Within about two days after the egg case is produced, it is placed in a sheltered area that contains abundant food. In about two months, nymphs emerge and are most active from spring until midsummer. In early spring, only adult oriental cockroaches are found; by late spring nymphs are abundant, and the adults begin to die off. By August, any oriental adults are new ones; by fall, most individuals are adults again.

Relative number of Oriental cockroach nymphs and adults during a calendar year (C. Ogg 1995).

As with the brown-banded species, egg cases are susceptible to drying out, attack by fungus and cannibalism by other cockroaches, if other food is scarce. The egg cases are often eaten by other insects as well and, if in an accessible area, by birds.

Behavior and Habitat. Oriental cockroaches are less wary and more sluggish than other cockroaches found in Nebraska. They are more sensitive to lack of water than other cockroaches and like cool, damp locations. Look for oriental cockroaches in dark, damp basements, crawl spaces, areas between soil and the foundation, underneath sidewalks, in sewer pipes, floor drains and any other cool, moist place. Outside, they sometimes aggregate near or under garbage cans.

Inspections. Inspections should concentrate in areas of high humidity and cool temperatures, as described above. In basements, infestations of these insects can sometimes be located by examining spider webs for evidence of oriental cockroaches. In homes without basements, look in crawl spaces. In kitchens and bathrooms, look around plumbing. Look for fecal smears, live or dead cockroaches and egg cases. Trapping is usually needed to detect low population levels. Low populations of oriental cockroaches may exist in a home, but home dwellers may only observe these cockroaches for a month or two in the spring when they are most active. Beware! Oriental cockroach numbers observed in the spring may appear low or under control, only to buildup by midsummer.

American Cockroach (Periplaneta americana)

Life Cycle. The American cockroach egg case contains approximately 14 eggs. It is often hidden in cracks or crevices several days after its formation. Nymphs emerge in about one to two months and undergo 13 molts, over the duration of six to 12 months, before reaching the sexually mature adult stage. The female can produce an egg case in about one week. Therefore, from 12 - 24 cases can be produced in the warm months of June, July and August. Adults commonly live more than a year, which gives them an entire life span of nearly two years.

It appears that the American cockroach has a tremendous potential for producing offspring, but because of cold winters, the American cockroach develops at a much slower rate in Nebraska. The result is a much lower potential for producing offspring in Nebraska than in southern states.

Behavior and Habitat. In Nebraska, American cockroaches can be found in commercial establishments like restaurants, grocery stores, bakeries and other places where food is prepared or stored. They are most common in boiler rooms, heated steam tunnels, basements around pipes, and around water heaters and wet floor drains. American cockroaches can coexist with German cockroaches with no negative effects on either cockroach population. These large cockroaches are not nearly as common in Nebraska homes as the three species mentioned previously.

Inspections. Inspections for American cockroaches should concentrate in areas of warmth and high humidity. Use methods similar for the Oriental cockroach to locate evidence of their presence. American cockroaches are known as "born inebriates", their desire for fermenting liquids is often very strong. There are many examples of restaurants or bar owners finding American cockroaches in partially empty beer bottles. Bread soaked with beer can be used to attract them. Ongoing inspections, including trapping are very important because of the long life span of this cockroach.

Wood Cockroach (Parcoblatta spp.)

Behavior and Harborage. Wood cockroaches live in rotted logs, tree stumps, hollow trees, stopped-up rain gutters, and in piles of fire wood. Males take flight during late spring in search of females. Males are attracted to light and sometimes accidentally invade homes, where they soon die. The best control method is exclusion, by tightening around screens, doors and windows. No chemical control is necessary.