Cockroaches use a variety of criteria in selecting harborage sites. In general, cockroaches orient to sheltered sites near food and water, and will remain true to a site as long as both are adequate (Ross et al., unpubl., in Bret et al., 1983; Rivault, 1990). Both the texture (Berthold, 1967) and orientation of surfaces (Bell et al., 1972) and the size of the harborage (Berthold and Wilson, 1967; Mizuno and Tsuji, 1974) are influential. Groups of cockroaches may segregate by body size, depending on the height of available space (reviewed by Roth and Willis, 1960).Small nymphs in the absence of older conspecifics prefer narrower crevices than do adults; however, they prefer larger harborages if other cockroaches are present, indicating that social stimuli supersede harborage height preferences (Tsuji and Mizuno, 1973; Koehler et al., 1994). Aggregation behavior of young nymphs is more pronounced in open areas than in shelters, suggesting that they may satisfy their thigmotactic tendencies with each other when the physical environment is devoid of tactile stimuli (Ledoux, 1945).
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