Cockroache; Ecology, behavior & history - W.J. Bell

EIGHT
Social Behavior
The only useful outcome of my attempt to classify types of parental care into
mutually exclusive sets was that it made clear that from many points of view by
far the largest group of insects that exhibit parental care (is) the cockroaches.
—H.E. Hinton, Biology of Insect Eggs
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-
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