Rehn and Hebard (1927) quoted observations made earlier by Hebard on _Byrsotria fumigata_ in Cuba: "I found the specimens under flat stones, sometimes in colonies of 3 or 4 mature specimens and numbers of immature individuals in all stages of development." These observers also reported that _Aspiduchus borinquen_ was found in Puerto Rico in a limestone cavern by thousands in the grass and on the walls. J. W. H. Rehn (1951a) stated that a related species, apparently _Aspiduchus cavernicola_, was seen in great numbers on the side walls and roof of a cave in Puerto Rico, but it was not possible to collect any of these and, we infer, confirm the species. Rehn and Hebard (1927) in their account of _Simblerastes jamaicanus_ reported finding it in numbers in a termite nest. Pemberton and Williams (1938) stated that _Diploptera punctata_ is of gregarious habits in Hawaii. Saupe (1928) observed a strong "herd instinct" in all age groups of _Blaberus craniifer_. Bunting (personal communication, 1956) stated that large nymphs and adults of _Blaberus discoidalis_ "congregate in narrow cracks or on the underside of some low object. The younger nymphs keep in close communities of approximately the same age." Sonan (1924) stated that in Formosa(?) _Salganea morio_ is usually found in groups of six or seven in decayed trees. Species of the genus _Litopeltis_ may be found in small groups as they are somewhat gregarious (Rehn, 1928). The physiological or psychological effects of gregariousness, or lack of it, are interesting aspects of the basic phenomenon. Landowski (1937) studied in _Blatta orientalis_ the effect on development and growth of the transition from life in complete isolation to life in groups. He kept nymphs in groups of 1, 2, 4, 8, and 16 in jars of identical size and shape. Landowski found that (1) mortality increased with the size of the group and with age, as each animal occupied more of the available space. [Presumably these factors are less detrimental in nature where the group is unconfined.] He further found that (2) life in complete isolation extended the time required to produce an adult insect; and (3) the mean weight of the adult insect was, generally, in inverse proportion to the number of nymphs raised together; isolated insects usually attained the greatest adult weight.