"The German Cockroach" (Blattella germanica)

The German cockroach, also known as the "steam fly" in England, is worldwide in distribution. It is the most prevalent species in and around homes, apartments, supermarkets, food processing plants and restaurants. Ships, especially cruise ships and naval vessels, also can be heavily infested.

The German cockroach is about 5/8 inch in length, brown in color, with two dark longitudinal streaks on the pronotum. The male is light brown and somewhat boat-shaped. The female is slightly darker in color with a broader and rounded posterior. This cockroach breeds throughout the year indoors, but favors a humid environment and an average temperature of approximately 70 degrees F.

The German cockroach produces more eggs per capsule than other pest cockroach species; and its young complete their growth in a shorter period of time. According to Noland et al. (1949), the German cockroach can grow from egg to adult in 36 days at 86 degrees F. However, in laboratories where the average temperature is approximately 80 degrees F with a 40 percent relative humidity, 50 to 60 days are required for it to reach the adult stage.

Female German cockroaches carry their egg capsules until they are ready to hatch, and the capsule often becomes as large as the abdomen. Gould and Deay (1940) investigated reproduction and egg capsule hatch in German cockroaches. The number of eggs in a capsule usually is between 30 and 40, with a maximun of 48. The average number of nymphs hatching from 59 capsules was 29.9. The average incubation period at 76 degrees F was 28.4 days. At a temperature of 76 degrees F, the developmental period varied from 54 to 215 days with an average of 103. They state: "At the time of hatching the seam edge of the capsule, while still held in the ovipositor of the female, may be opened by the hatching nymphs, or the capsule may be dropped several hours or perhaps a day previous to the escape of the young. Capsules removed from the female do not hatch unless this act is performed only a day or so before hatching." According to Gould and Deay (1938), the egg capsule, in hatching, split open along the seam, and the white heads of the numerous young cockroaches then appeared. Then, after "much struggling and squirming, about 12 worked themselves out and were soon pulling their legs and antennae free from their individual egg shells."

According to Laing (1938), "in this species the mother cockroach is interested in her young and may aid them to escape from their swadding clothes. The larvae run actively as soon as they are born. It appears as though the females far outnumber the males." Ross (1928) and Rau (1944) observed the young to emerge from the egg capsules while these were still been carried by the mother, and they observed some females carrying the egg capsule even after the young had emerged. Individual females at room temperature may produce an average of four to five capsules (Gould and Deay, 1940) in their lifetime or one capsule every 20 to 25 days. Some females may live more than 200 days.

Ross (1928) studied the life history of this cockroach at a temperature of 95 degrees F and at 90 to 95 percent relative humidity. A life cycle was completed in about three months. The egg stage required 14 days, and the seven nymphal instars 60 days for males and 65 days for females. The number of eggs in the egg cases varied from 18 to 50 an ample moisture supply was required for their complete development. The number of days for development, from hatching to the adult stage, varied from 55 to 68. He also observed, unlike Gould and Deay (1938), that the males and females ordinarily were present in approximately equal numbers. Ross makes this interesting observation: "It is curious to note that the younger females, even when carrying an ootheca, can walk upside down on dry glass with the utmost ease; but shortly after the first ootheca has been dropped, the females lose this power and cannot walk up even a vertical surface of glass." W.C. Easterlin has observed that first and second instar American and oriental cockroaches were incapable of climbing vertical glass surfaces, whereas the older instars have no difficulty in doing so.

The German cockroach is spread by commerce and transportation, as well as by its migrations. Many homes and business establishments become infested with German cockroaches when they are introduced in infested cartons, foodstuffs and other materials. It may be of interest to describe a home in Austin, Texas, that had an unusually high population of German cockroaches. This four-room apartment was sprayed on Aug. 1, 1947, with approximately 3.5 quarts of an experimental contact spray. The cockroach population was estimated to be 50,000 to 100,000 cockroaches, the greatest number by far being German cockroaches. For the most part they were present in the kitchen. It may be an understatement when we noted that the housekeeping was poor. On Aug. 25 and Sept. 17, 1947, the apartment was examined for cockroaches, and pyrethrum aerosol spray was used to flush the cockroaches out of their hidding places. No effort was made to kill the cockroaches. An estimated 400 to 1,000 German cockroaches were found on this respective dates.

On Jan. 21, 1948, approximately six months after the initial spraying, the house once again was inspected for cockroaches. Although this was a sunny day, the interior of the house was dark due to the drawn window shades. On approaching the wood shelving over the kitchen sink in order to flush the cockroaches out with the aerosol spray, it was observed that the shelves were covered with plates in an upright position, and German cockroaches of all stages were clustered on the walls in great numbers, particularly in the corners where the shelves joined the sides of the open cupboard. Apparently there were so many cockroaches in the cracks and crevices between and behind the shelving that the cockroach population overflowed on the walls into the open, which is unusual for German cockroaches. On directing the aerosol into the cracks and crevices, the German cockroaches began to emerge immediately in enormous numbers and scurried frantically over the walls and ceilings. Upon lifting the oil cloth of the kitchen table, the edge of the table was found to be encrusted by a great mass of German cockroaches. These began to fall like rain drops and frantically scatter upon contacting the mist from the aerosol container. It is estimated that there were approximately 15,000 to 25,000 German cockroaches in this infested kitchen six months after treatment with a contact spray.

During the summer of 1979, Linindoll Pest Control took on what was perhaps the largest German cockroach population ever within a two family dwelling. Called in the Board of Health in Schenectady, N.Y., the company was faced with so many cockroaches that the wall of every room was saturated. It was estimated that over a million cockroaches were present. The population had overflowed outdoors. The lawn and walls of surrounding buildings also were heavily infested. Sewers within a three block area were heavily infested with German cockroaches. The house in question harbored a population of 24 dogs, 20 cats, two mice and a parrot. Many of the animals were badly bitten by cockroaches. The house was ordered destroyed. Because there were so many cockroaches present, standby power sprayers were necessary to kill cockroaches as the walls of the building were detroyed.

The German cockroach is the most prevalent pest in low income apartments in the United States. Koehler et al. (1987) sampled with sticky traps the interiors of 1,022 low income apartments in Florida to determine the severity of German cockroach infestations. Median catches were 28 cockroaches per night per trap. Heaviest infestations were found next to the garbage container with median trap catches of 36 cockroaches per trap. German cockroach populations in half of all apartments were estimated to exceed 13,000 cockroaches. Examination of trap data through time indicated that populations increased in the summer months. Apartments receiving monthly pest control service did not have lower cockroach populations than those without monthly service. More than 95 percent of all apartments had populations greater than those commonly considered tolerable.

Although uncommon German cockroaches can survive outside. In 1966, German cockroaches were seen surviving on rotten pears outdoors in Indianapolis, Ind. In the early 1970s, a heavily-infested home in Nashville, Tenn. produced an excess population in the surrounding grass and on the exterior of structures.

On one occasion, thousands of German cockroaches were observed harboring inside a large radio located in a patients' lounge of a hospital. There was no moisture source within 60 feet. Upon questioning some of the staff, it was learned that the cockroaches often rushed out to drink human urine produced by patients who could not control themselves.