Shaw (1925) claimed that Supella supellectilium tended to oust Blattella germanica, but Pope (1953) thought it doubtful in Queensland. Wolcott (1950) stated that "The larger and more powerful domestic cockroaches, Periplaneta americana (L.), P. australasiae (F.) and P. brunnea Burmeister have very definitely fallen behind in Puerto Rico in competition with the little German roach." Pessôa and Corêa (1928) observed that other species of cockroaches were rare in Brazil in houses that were infested with Leucophaea maderae. Lederer (1952) noticed that in the reptile house of the aquarium at Frankfort am Main Blatta orientalis was obviously kept down by Blattella germanica, even before the appearance of P. americana. However, B. germanica was not driven out of the reptile house by P. americana although the populations of each fluctuated for about 22 years after the American cockroach had settled there; both species occupied separate resting places. Lederer further observed that within four years of the introduction of P. americana into the crocodile house, none of the original infestation of B. orientalis could be found; a small colony of Pycnoscelus surinamensis in the reptile house was apparently also driven out by P. americana. Chopard (1932, 1938) stated that the oriental cockroach does not exist in company with P. americana which very probably destroys it. Pettit (1940) kept B. germanica and P. americana together in a cage for several weeks but neither species gave any indication of feeding on the other.
Froggatt (1906) stated that "It is probable that the advent of the larger and more formidable American cockroach into Australia has led to the retirement or destruction of our indigenous species" [presumably Periplaneta australasiae]. Tillyard (1926) noted that this statement is incorrect as neither species is native to Australia. Yet Shaw (1925) stated that in Australia "When both species live together in the same places, australasiae Fabr. will probably be found gradually to displace americana L." Local fluctuations in the relative abundance of these species could be a basis for such dissimilar observations. However, MacDougall (1925) observed that in the plant houses of the Royal Botanical Garden, Edinburgh, the Australian cockroach seemed to have overcome the American which had been more numerous in former years.
In conclusion, we emphasize that many of the above observations are merely tentative impressions gathered by workers who have watched many species of cockroaches in nature. Obviously, additional observations coupled with appropriate experimentation will be needed to disclose the true structure of each presumed association and to resolve apparent discrepancies. Although we are greatly indebted to the cited authors for their contributions to the known information, we anticipate that future results of cleverly designed laboratory experiments will do much to dispel the uncertainty that still surrounds our knowledge of the relations of the Blattaria to each other.
[XVIII. DEFENSE OF COCKROACHES AGAINST PREDATORS]
Irritating or repellent secretions provide many animals belonging to widely unrelated groups with a more or less potent means of defence....
It will be seen that this method of defence does not rest merely upon a passive unpalatable attribute, but upon an active emission of the unpalatable substance which, since it occurs when the animal is seized or threatened by an enemy, enforces its effectiveness. In its highest development we find different forms whose specialized habits and modified structure enables them to project secretion at the enemy, and thus to discourage attack.
Cott (1940)
There are very few records indicating that cockroaches are unaccepted as food by other animals. Hutson (1943) found that the duck, guinea fowl, and pigeon would not normally eat Pycnoscelus surinamensis, and in his experiments with the chicken eye worm he had to force-feed his birds with infected cockroaches. Lederer (1952) found that insectivorous birds in the Zoological Garden, Frankfurt am Main, either refused hardened (as opposed to teneral) American cockroaches or ate them unwillingly. Carpenter (1925) reported that a monkey (Cercopithecus) failed to feed on cockroaches and suggested that the insects' odor made them repugnant; however, there are a number of positive records of monkeys feeding on cockroaches (see pp. [284]-[286]).
Cockroaches may escape capture by predators through evasive behavior, concealment, protective coloration, mimicry, or secretion of malodorous materials. Nocturnal cockroaches may avoid predators that are active during the day (Crawford, 1934), but nocturnal predators are apparently quite successful in capturing cockroaches. Some cockroaches may be protected by their swiftness, others by their resemblance to vegetation (Williams, 1928). The habit of squeezing into narrow cracks may afford cockroaches some protection.
Burrowing forms such as Pycnoscelus may spend much time in underground cells (Roeser, 1940). Polyphagids rapidly burrow into sand (Fausek, 1906), where they may be protected from predators. Tepper (1893) discovered that a very large Australian cockroach, Geoscapheus robustus, had its fore legs, especially the tibiae, adapted for digging. He observed this species in captivity and in 1894 reported that it appeared to sink into the soil without raising any considerable amount above the surface and that it did not form an unobstructed tunnel. Another large Australian cockroach, Macropanesthia rhinocerus, burrows about two feet below the surface of sandy soil; it also makes nests among pine roots and the nymphs rarely appear above ground (Henson in Day, 1950). Tepper (1893) observed that Australian cockroaches of the genera Epilampra and Oniscosoma buried themselves in loose soil and dust. Baker (in Rehn, 1930) observed that Styphon bakeri is found in humus and rubble in the Dutch West Indies where "It is sluggish in the open, but wedges into the humus quite quickly."
Therea nuptialis, found in India, conceals itself at the roots of fig trees, etc. The small hairs on its elytra retain sufficient dust to conceal it, or at any rate to render it inconspicuous, when not on the wing (Annandale, in Chopard, 1924c). Rehn and Hebard (1914) observed that the nymphs of Blaberus craniifer[13] at Key West, Fla., "were usually found half buried in loose damp earth under boards, where they remained motionless, looking much like lumps of earth (with which they were usually much dusted) until disturbed." Hebard (1917) reported of Monastria biguttata from Brazil that "All of the juveniles are heavily coated with foreign particles" which adhere "to a multitude of closely placed, minute and usually curved spines, which cover the dorsal surface and marginal portions of the ventral surface."