332 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. I4I 



Periplaneta americana was observed by Gould and Deay (1938) in 

 an old meat-packing building in Indiana. Adult cockroaches were 

 present in large numbers between closely placed beams, but the 

 nymphs were more common in cracks between bricks. Clusters of 

 several hundred cockroaches were seen on the open walls of the cold, 

 dark hide room. Gould and Deay stated "American roaches of all 

 sizes live together in perfect harmony. Young nymphs have been 

 noted in clusters underneath adults and crawling over the adults as 

 they wander about in rearing jars." In the monkey house of the Ham- 

 burg zoo, P. americana spent most of the day in the cellars resting on 

 the walls in groups of about 200 individuals (Brecher, 1929). Lederer 

 (1952) noted that in closed, dark, heated spaces under the aquarium 

 at Frankfurt am Main, P. americana rested in groups of 20 to 30 

 individuals ; he stated that it was remarkable that the "herd" divided 

 itself into groups each of which usually contained insects of the same 

 age or stage of development. Eads (1954) found P. americana in 40 

 percent of 762 sewer manholes in Tyler, Tex. ; 13 percent of 670 of 

 these manholes were heavily infested with 100 or more cockroaches 

 in each. Other heavy sewer infestations have been reviewed in our 

 1957(a) paper. 



Ehrlich (1943) has stated that Periplaneta americana exhibits social 

 behavior. For instance, cockroaches of various ages inhabit a fairly 

 large space jointly; the adults and older nymphs sense approaches 

 with their antennae and warn and protect the young by a beating of 

 wings and by body movements. There is complete utilization of the 

 available living space ; the imagos drive older nymphs from their 

 resting places, and the older nymphs drive out the younger ones, until 

 all cracks, depending on their size, are occupied by various age groups 

 of different sizes. In his experiments Ehrlich observed that in cages 

 with no hiding places the cockroaches would group together ; when 

 given a choice of small and large shelters, P. americana hid only under 

 the larger ones that could shelter more insects. Finally, the cock- 

 roaches ceased to bite and fight each other when they crowded to- 

 gether in the face of danger. 



Of Blatfa orientalis Marlatt (191 5) stated "This species is notably 

 gregarious in habit, individuals living together in colonies in the most 

 amicable way, the small ones being allowed by the larger ones to sit 

 on them, run over them, and nestle beneath them without any resent- 

 ment being shown." Haber (1919) also observed that this species is 

 often noticed "huddled together, the younger ones crawling over, 

 around, and beneath the older ones." 



Wille (1920) observed that nymphs of Blattella germanica re- 



