For years it has been believed that cockroaches feed on bedbugs (Cimex lectularius L.) and this statement has been repeated in many reference works and articles. Ealand (1915) stated that cockroaches devour bedbugs with avidity. Even today similar statements are to be found in the literature. "In the old sailing ship days, they [cockroaches] were often welcomed by crews because of the belief that they would eradicate a population of bedbugs. This belief was based on scientific fact, as cockroaches are known as predators of bedbugs" (Monro, 1951). Cockroaches will often "help rid a house of bedbugs by devouring all the little parasites they can capture" (Gaul, 1953). The basis for this belief may have originated with a statement by Webster (1834) who wrote that bedbugs disappeared aboard "H.M. Sloop Chanticleer" when cockroaches made their appearance. Newman (1855) reported the observations of a friend who claimed to have seen a cockroach seize a bedbug in an infested boardinghouse in London. In 1920 Purdy reintroduced cockroaches into a house from which they had been exterminated, in order to control the bedbugs which had become established. According to a popular account by Lillingston (1934) African natives are said to ask sailors for a cockroach or two to be used to hunt bedbugs.
In Siberia, Burr (1926, 1939) found Blattella germanica and bedbugs inhabiting the same room. Mellanby (1939) studied the populations of an animal house in which bedbugs and cockroaches occurred in large numbers; the bugs apparently were not attacked and their numbers increased greatly over a period of a few weeks (Johnson and Mellanby, 1939). Wille (1920) placed starved B. germanica with bedbugs for 20 days, but the cockroaches failed to attack the bugs. In India, captive adults and nymphs of two species of house cockroaches would not touch living bedbugs or their eggs (Cornwall, 1916). In laboratory experiments Gulati (1930) found that Periplaneta americana ate young bedbugs which had soft, blood-filled abdomens; adult bedbugs with harder exoskeletons sometimes were rejected. The maximum number of bedbugs eaten by a cockroach was 3 out of 12 during a period of 48 hours. Johnson and Mellanby (1939), also in laboratory experiments, were unable to show that bedbugs can be controlled by Blatta orientalis or that bedbugs are eaten to any extent by them. The existing evidence indicates that there is little basis for the often repeated statement that cockroaches destroy bedbugs in nature. As Lorando (1929) pointed out, assassin bugs, cockroaches, and red ants can hardly be considered as practical factors in bedbug control, though he did recommend the use of spiders.
According to Martini (1952), cockroaches prey on mosquitoes and sand flies but we have been unable to find any original sources for these statements; the only reference we have found in which cockroaches and Phlebotomus are mentioned together is a paper by Whittingham and Rook (1923); they fed ground-up cockroaches to larvae of Phlebotomus papatasii. Wharton (1951) reported that cockroaches and other predators attacked mosquitoes knocked down by insecticides and affected the number recovered.
Cockroaches will on occasion attack and bite animals other than insects. In an earlier paper (1957a) we discussed about 20 reports of cockroaches biting man. The injury is usually confined to abrasion of the callused portions of hands and feet but may result in small wounds in the softer skin of the face and neck. We failed to include the following reference in the above-mentioned paper. Sonan (1924) had his toes and breast nibbled by cockroaches on Hiyakejima Island during sleep. He had previously learned from a policeman that Periplaneta americana and P. australasiae nibbled people on that island, but he had hardly believed it before he experienced the biting himself.
INTRASPECIES PREDATION
Those who have reared cockroaches in the laboratory have undoubtedly seen cannibalism occur in the cultures. Cannibalism has been observed among the common domiciliary species of cockroaches as well as laboratory colonies of Leucophaea maderae (Scharrer, 1953), and Blaberus craniifer[12] (Saupe, 1928). Edmunds (1957) reported that cannibalism was common in a laboratory colony of Periplaneta brunnea and that egg capsules deposited by a female were often eaten by the other cockroaches.
Periplaneta americana occasionally ate other cockroaches and their oöthecae and also attacked members of their own species (Lederer, 1952). Griffiths and Tauber (1942) recorded the killing of male American cockroaches by females of the species: "One female was especially vicious and attacked each new male as he was introduced into the container. Most of such males had molted less than 2 days previously. Older males were more capable of defending themselves against attacks of these cannibalistic females." Even though adequate food may be present, females of Periplaneta americana may eat their own eggs (Klein, 1933). Some females may regularly eat their oöthecae as soon as they are dropped (Griffiths and Tauber, 1942). To be completely eaten an oötheca generally must be attacked before it has hardened. If a hole is eaten in one side of the capsule, the cockroach may devour the eggs and leave a portion of the oötheca. Frequently only the keel or a part of the keel is eaten and when this occurs the eggs fail to hatch and usually do not complete development because of the rapid loss of water (Roth and Willis, 1955). When adults of P. americana and P. australasiae were deprived of food, both males and females ate newly deposited eggs and, finally, the females ate the males (Sonan, 1924).
Parcoblatta virginica in laboratory cultures also may eat part of its oöthecae; in this species only the soft end of the recently deposited oötheca was eaten (Roth, unpublished data, 1957).
Cros (1942) observed oöthecae-bearing females of Blatta orientalis attack and kill males of the same species which were attempting to mate; these males were then eaten by the females. Cros also observed injured and recently molted nymphs of B. orientalis to be eaten by others of the same species.
Pettit (1940) noted that cannibalism in his culture of Blattella germanica occurred only when the insects were molting. Adult insects attacked the molting cockroaches more often than did the nymphs. However, nymphs after the fourth instar occasionally set upon other molting nymphs. First-to third-instar nymphs rarely victimized their mates. The victims were all older than third instar; the later stadia were progressively more subject to attack, and molting adults suffered the greatest mortality. No direct correlation was noted between population density and cannibalism.