y2 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. I4I 



humidity (Willis and Lewis, 1957). Blatta orientalis, when in a state 

 or normal water balance, usually spent more time in the drier part of a 

 humidity gradient ; but desiccated insects tended to become hygro- 

 positive (Gunn and Cosway, 1938). We presume that other domi- 

 ciliary species behave similarly. If water is available nearby, it may 

 be presumed that partially desiccated cockroaches could locate a 

 source through the mediation of a humidity sense. Hygroreceptors 

 have been demonstrated on the antennae of Blattella germanica (Roth 

 and Willis, 1952a) and suggested for Blatta orientalis (Gunn and 

 Cosway, 1938). 



Drinking water is available to cockroaches in the traps of sinks, 

 wash basins, tubs, and toilet bowls ; in flush tanks ; as condensation 

 on cold pipes, flush tanks, and windows ; around leaking pipes and 

 faucets ; as spillage ; in miscellaneous water-filled containers, such as 

 pet drinking dishes, aquaria, vases ; empty beverage bottles ; and 

 drainage from ice boxes. Soft, juicy fruits and vegetables can provide 

 both moisture and food. There seems to be a tendency for certain 

 species {Blatta orientalis and Blattella germanica) to become estab- 

 lished in the more humid parts of structures, such as basements, 

 around sinks, and in bathrooms. Whether this is a reaction to a 

 preferred humidity or merely a fortuitous aggregation near sources of 

 drinking water and food has never been clearly demonstrated. The 

 rather widespread dissemination of these species into zones of low 

 as well as high humidity suggests that detailed studies of the micro- 

 climatic conditions of structural microhabitats will be needed before 

 meaningful conclusions can be drawn about the stratification of cock- 

 roaches within structures according to species. 



In nearly all structures infested by cockroaches, food of some kind 

 is available, either in the structure itself or nearby. This may be the 

 food stored by man for his own use or the use of kept animals ; it may 

 be crumbs, food spillage, garbage, or excreta ; glues and pastes on 

 cartons, boxes, stamps, envelopes, labels, and wall paper ; sizing on 

 cloth and book covers ; various dried animal and plant products ; dead 

 insects ; living plants ; etc. In fact, it is almost impossible, despite good 

 housekeeping, to keep any structure used by man free of all food 

 suitable for cockroaches. 



That the requisite temperature, water, and food are provided, more 

 or less adequately, by a variety of structures is attested by the 

 innumerable infestations of cockroaches that develop when control 

 measures are relaxed. Within structures the accessibility of certain 

 harborages to cockroaches probably depends on the habits of the 

 species and to some extent on their size. Similar types of harborages 



