Hidden in plain sight: Cryptic pupation behavior of Necrobia rufipes and Dermestes maculatus

Late-stage colonizing beetles provide critical entomological evidence in cases where dipteran indicators are absent or degraded; however, their pupation ecology remains insufficiently documented, particularly regarding microhabitat selection. The present study investigated substrate-specific pupation preferences of two forensically important coleopterans, Dermestes maculatus (Dermestidae) and Necrobia rufipes (Cleridae), under controlled laboratory conditions, with particular emphasis on concealed pupation microhabitats. Choice-based experiments were conducted using multiple potential indoor substrates, including wood, foam, empty dipteran puparia, and larval exuviae of D. maculatus. Both species exhibited non-random and species-specific pupation behavior. D. maculatus showed a strong preference for empty dipteran puparia. In contrast, N. rufipes displayed greater behavioral flexibility and repeatedly pupated within empty puparia and D. maculatus exuviae, sealing the exuvial openings to form compact and inconspicuous pupation chambers. To our knowledge, this represents the first documented evidence of N. rufipes utilizing dermestid exuviae as pupation substrates. Statistical analyses (likelihood ratio G-tests and Fisher's exact tests) confirmed a highly significant association between species identity and substrate use (p < 0.001). Recognition of these concealed pupation sites can improve recovery of immature beetle stages and enhance minimum postmortem interval estimation in advanced decomposition cases.