It is difficult to conceive of any group of animals that are as universally and diversely social as cockroaches. Given the range of habitats they have mastered and their versatility in reproductive mode and feeding habits, it is unsurprising that they exhibit extraordinary variation in their social organization. Individual taxa are typically described as solitary, gregarious, or subsocial. We structure this chapter around those categories, treating each in turn, with the caveat that this simplistic pigeonholing masks the head-banging vexation we encountered in attempting to classify the social heterogeneity present. Cockroaches that live in family groups are a rather straightforward category, and domestic pests and a number of cave-dwelling species are without a doubt gregarious. For a variety of reasons many others elude straightforward classification. First, the majority of cockroaches are unstudied in the field, and the nature and frequency of social interactions have been specified in few species. With perhaps a score of exceptions, our concept of cockroach social organization is largely based on anecdotal evidence and brief observations noted during collection expeditions for museums. Second, cockroaches are often assigned social categories without specifying the employed criteria, and the terms describing their social tendencies have been used in a vague or inconsistent manner (discussed below). Third, evidence to date suggests that sociality in Blattaria is not as straightforward as it is in many insects. There is considerable spatial and temporal variation in social structure, influenced by, among other factors, the age and sex of the insects, environmental condition, physiological state, population density, and harborage characteristics. Fourth, many cockroaches are nocturnal and cryptic; consequently even those that live in laboratories can be full of surprises. Parental feeding behavior was only recently observed in Gromphadorhina portentosa, a species commonly kept in homes as pets, in laboratories for experiments, and in museums for educational purposes (Perry and Nalepa, 2003). Fifth, even closely related species can vary widely in social proclivities. The German cockroach Blattella germanica is strongly gregarious; it has been the test subject of the vast majority of studies on cockroach aggregation behavior. Its closely re-
lated congener B. signata, however, is apparently solitary (Tsai and Lee, 2001). Sixth, laboratory data can conflict with field descriptions. One example: studies on Schulte-sia lampyridiformis reared for 20 yr in the laboratory suggest that females use aggression to disperse nymphs after hatch (Van Baaren and Deleporte, 2001; Van Baaren et al., 2003). In the field (Brazil), however, Roth (1973a) found adults and nymphs living together in birds' nests. One nest contained 4 males, 8 females, and 29 nymphs, and other cockroach species were also present. Lastly, the division of species into group living and solitary categories is largely artificial in any case because most animal species are in an intermediate category, found in association with conspecifics at certain times of their lives, but not others (Krause and Ruxton, 2002).
These issues, and others, have bearing on phylogeneti-cally based comparative analyses of cockroach social behavior. While these can be powerful tools for generating and testing ideas about the links between behavior and ecology, attempts to map social characteristics onto cladograms of cockroach taxa are premature. We are still early in the descriptive phase of cockroach social behavior, and unresolved phylogenies in many cases preclude meaningful comparative study. Some general trends are detectable and will be discussed below.
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