Eads (personal communication, 1955), in response to our inquiry about the mixed populations of cockroaches that he had reported infesting sewers in Texas (Eads et al., 1954), stated that "Each of the ten colonies of _B. orientalis_ found in Tyler manholes were associated with larger colonies of _P. americana_. True breeding colonies of _B. orientalis_ appeared to be present since all the developmental stages were taken. The same situation existed with the _P. fuliginosa_ and the two species of _Parcoblatta_. Larger colonies of _P. americana_ were associated with the other species in each case. From our limited observations the two species always appeared to be perfectly compatible." Eads et al. (1954) had found _Periplaneta fuliginosa_ in three manholes, _Parcoblatta bolliana_ in one manhole and _Parcoblatta pensylvanica_ in one manhole. We assume that the groups of each species were spacially discrete so that they were recognizable as colonies. Dr. T. A. Olson (personal communication, 1958) has observed two or more species of cockroaches in a single structure but never in mixed colonies. Each species was separated physically from the others. Olson concluded that cockroaches of different species do not mingle freely unless forced to do so by some special environmental condition. Pettit (1940) found _B. germanica_ and _P. americana_ similarly separated in the same building or even in the same basement laboratory. Perkins (1899) found _Lobopterella dimidiatipes_ generally living in company with the young of _Periplaneta australasiae_ in Hawaii. Rehn and Hebard (1914) in Florida found _P. australasiae_ abundant with _Periplaneta americana_ on a quarter-boat. They also noted that the forficulid _Marava_ [= _Prolabia_] _arachidis_ (Yersin) appeared in numbers in a kitchen after dark accompanied by swarms of _P. americana_. These workers also found _Leurolestes pallidus_ in a fruit store in Key West "where the species was common in a pile of old burlap bags and in cracks under the stands which it shared with one fairly large colony of _Blattella germanica_, occasional specimens of _Holocompsa nitidula_, a few specimens of _Periplaneta americana_, and one specimen of _Supella supellectilium_." They also found _H. nitidula_ with _Blaberus craniifer_ "between old boards in a woodshed, where nymphs were more numerous than adults."