ROACHES

roachd315 The American cockroach, or “Bombay canary” as it is known to the English dockhands, is the largest of the house-infesting cockroaches, being 1 1/2 inches long with fully developed reddish brown wings and light markings on the thorax.

The cosmopolitan American cockroach likes the seafaring life, and is one of the most common cockroaches on ships. Kellogg (1908) says a friend of his in Mazatlan, Mexico, sent him quarts of large American cockroaches which he scooped up from his bedroom floor.

He goes on to state that ships came into San Francisco with the sailors wearing gloves on their hands while asleep to keep the hordes of cockroaches from gnawing off their fingernails. This cockroach is commonly found in sewers and basements, particularly around pipes.

Schoof and Siverly (1954), as well as other investigators, show this cockroach to be a common inhabitant of sewage systems. Observations after heavy rain show that basements in numerous cities throughout the United States have increased populations of American cockroaches.

Much of the following material on the life history of the American cockroach is from Gould and Deay (1940) who made a detailed study of this species. Rau (1940) notes the egg capsule is not dropped as soon as it is formed, but may protrude from the body from a few hours up to four days.

Egg capsules are often glued to surfaces. In Florida, egg capsules are frequently found covered with paint or other building material, blending well with the surroundings. According to Rau (1943), cockroaches “do not drop the egg cases indiscriminately, but usually hide them with great care in crevices, or bury them in softwood or workable material.”

This clearly has survival value since predators and parasites attack poorly protected egg capsules or pest control technitians may squash egg capsules easily spotted around exterior door frames. Rau (1940) showed that the incubation period was from 38 to 49 days, and the number of egg cases produced by the female was from six to 14, with an average of 9.5. The eggs in egg capsules are in two parallel rows, and the number of eggs in a capsule is variable.

The first few capsules produced by a female may contain a full complement of 16 eggs. However, the average number of young to emerge from 511 fertile capsules was 13.6. According to Gier (1947), “Eclosion, or hatching, occurs when all embryos are developed enough to exert sufficient pressure to open the ootheca. As soon as the cement on the lips of the ootheca is broken, all nymphs wriggle out, molting their embryonic skins as they do so. If one or two fail to emerge when the others do, they perish, as they are not able to force the ootheca open again.” The whitish, newly-emerged nymphs begin to run around actively in about 10 minutes.

The first few molts of the nymph occur at approximately monthly intervals, but thereafter may vary from one to six months. Gould and Deay (1940) state, “The American cockroach apparently molts 13 times before reaching maturity. The duration of the nymphal period from records now available varies from 285 to 616 days, with an average of 409, although the final average will be over 450 days. One individual hatching on January 11, 1936, was still in the eleventh instar, being 786 days old. Growth is slower during the winter months, although maturity is reached any month in the year. The average development period of six male nymphs was 426 days and that of 11 females was 396 days.” Gier (1947) showed that at 86 degrees F this cockroach normally has 10 instars which gradually increase from 18 days for the first, to 50 days for the tenth. He also found that body weight approximately doubles between molts and the cockroaches may reach sexual maturity in seven months under optimum conditions. In the laboratory, approximately 24 weeks are required from egg to adult at 80 degrees F. and R.H. of 50 percent. The wing pads become evident in the third or fourth instar. The sexes in the early instar are distinguished by the fact the female has a sharp medial notch in the caudal margin of the ninth sternum which is either lacking or very slightly indented in the male.

Gier (1947) states the American cockroach may reach sexual maturity in seven months under optimun conditions. The sexes are almost identical in size, the females average 34.7 mm and the males 33.6 mm. The female has a broader abdomen that the male. However, only the male has both cerci and stylets. The wings of the male extend from 4 to 8 mm over the end of the abdomen, while in the female they are equal to or only slightly larger than the abdomen.

None of Gier’s (1947) females reproduced parthenogenetically, but a colony of female American cockroaches that reproduces only by parthenogenesis has been selected in Gainesville, Fla. Roth and Willis (1956) showed parthenogenesis does occur in the American, oriental, German and brown-banded cockroaches, as well as in Nauphoeta cinerea. A female cockroach need mate but once to produce more than one capsule. In Indiana, during the months of June, July and August, a female may produce capsules at intervals of approximately four days. These intervals may lengthen to 12 days during the winter. One female produced 58 capsules, of which 33 were fertile. The maximum number of capsules produced was 90.

The sexes are approximately equal in number. Adult females lived from 102 to 588 days, with an average of 440 days. The life spans for three females were 783, 793 and 913 days. Gould and Deay (1940) observed the mating procedure of American cockroaches: “In pairs found in copula the cockroaches were usually headed in opposite directions. Amatory actions of the males are a common sight at night. They walk around with their abdomen distended, legs stiffened and their wings erect, and attempt to back under the female. Copulation was of short duration when there were many individuals in a jar, but where single pairs were in a jar, it may last for 30 minutes or longer.”

The ability of American cockroaches to survive the winter outside under certain conditions was confirmed by observations at an open dump in Waltham, Mass. Numerous American cockroaches were found thriving under several inches of snow in smoldering refuse when the outside air temperature was well below freezing. As material under the snow was turned over, American cockroaches scurried in all directions.

The American cockroach has become a sort of folk hero in the United States. During the past few years, contests to find the largest cockroach have been held throughout the country. The winners of regional contests were entered in the national runoff held in conjunction with the Smithsonian Institute in Washington, D.C. Winning American cockroaches were 2.10 inches in length. All cockroaches entered in the contest had to be dead in order to compete.