334 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. I4I 



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 Aspi- 

 duchus 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 

 of these and, we infer, confirm the species. Rehn and Hebard (1927) 

 in their account of Simblerastes jammcanus reported finding it in 

 numbers in a termite nest. Pemberton and Williams (1938) stated 

 that Diploptcra punctata is of gregarious habits in Hawaii. Saupe 

 (1928) observed a strong "herd instinct" in all age groups of Blaherus 

 craniifer. Bunting (personal communication, 1956) stated that large 

 nymphs and adults of Blaherus 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 Lito- 

 peltis 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 i, 2, 4, 8, and 16 in jars of 

 identical size and shape. Landowski found that (i) mortality in- 

 creased with the size of the group and with age, as each animal occu- 

 pied 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 in- 

 sect was, generally, in inverse proportion to the number of nymphs 

 raised together; isolated insects usually attained the greatest adult 

 weight. 



Similarly, Griffiths and Tauber (1942a) found that isolation ex- 

 tended the period of nymphal development in Periplaneta americana. 

 As most of their isolates died before reaching maturity, these workers 

 concluded that the American cockroach does not thrive when in- 

 dividually isolated and that several individuals must be together for 

 optimum development to occur. Pettit (1940, 1940a) observed that 

 isolated nymphs of Blattella gerrnanica take longer to mature than 

 those reared in groups. Wallick (1954) found indications in B. 

 gerrnanica that there is an inverse relationship between population 

 density and individual weight ; as the population decreased the weight 



