In contrast to the presumably amicable associations mentioned above, other observations in the literature seem to indicate that some species of cockroaches are incompatible when they attempt to occupy the same habitat niche. Marlatt (1915) stated "Rarely do two of the domestic species occur together in the same house. Often, also, of two neighboring districts one may be infested with one species, while in the other a distinct species is the commoner one. The different species are thus seemingly somewhat antagonistic, and it is even supposed that they may prey upon one another, the less numerous species being often driven out." Phelps (1924) stated "Roaches of different species are rarely found together, although roaches of the same species live together on very amicable terms." In 1859 Darwin (1887) stated that "In Russia the small Asiatic cockroach [_Blattella germanica?_] has everywhere driven before it its great congener [_Blatta orientalis?_]." Yet in France Girard (1877) suggested that the oriental cockroach be introduced into a restaurant infested with the German cockroach as the best way to expel the latter, because the more robust species drives away cockroaches of smaller size. Wille (1920) in Germany found usually only one species of cockroach in a house. Yet when he placed _B. orientalis_ and _B. germanica_ together, there were no reciprocal attacks even by hungry individuals. Wille concluded that because of their greater speed, smaller size, greater number of eggs, and faster development, the German cockroaches eat the available food and so make the environment unfavorable for the oriental. However, he noted that cases may be seen in which the opposite is also possible. Laing (1946; British Museum [Natural History], 1951) observed that in the British Isles _B. orientalis_ seems to have lost its dominant position to _B. germanica_ in recent years; it was stated that these species are not as a rule found together and that the greater rapidity of breeding and ability to climb of _B. germanica_, as well as the layout of modern buildings, are some of the factors that favor the spread of _B. germanica_. Ledoux (1945) found that first-instar nymphs of _B. germanica_ and fourth-instar nymphs of _B. orientalis_, adults of _B. germanica_ and sixth-instar nymphs of _B. orientalis_, as well as adults of both species, did not form mixed groups. However, when he combined fifth-and sixth-instar nymphs of _B. germanica_ with fourth-and fifth-instar nymphs of _B. orientalis_, which are all practically of equal size, sometimes he would find mixed groups, but generally the groups were distinct. Lucas (1912) stated that Burr had found _B. germanica_ and _B. orientalis_ swarming within a rubbish heap in England; presumably both colonies were breeding and multiplying and one species was not detrimental to the presence of the other.