Heads or tails: an analysis of dung beetle (Coleoptera: Scarabaeidae: Scarabaeinae & Aphodiinae) attraction to small mammal carrion
Necrophilous insects occupy a biologically interesting ecological niche because carrion is a highly desirable but ephemeral food source. Insects that feed on carrion are widely studied in forensic and entomological disciplines, but many taxa attracted to decomposition are often overlooked. Dung beetles (Coleoptera: Scarabaeidae: Scarabaeinae and Aphodiinae) are frequently found at carrion, but very little is known about their attraction to this resource. Are dung beetles attracted to the carrion itself or are they attracted indirectly because the gastrointestinal contents of the animals are exposed? This research attempts to disentangle the association between dung beetles and carrion by examining the distribution of dung beetles on the head- and tail-end of rat carrion, delimiting a resource more attractive to necrophagous insects (head-end) and a resource more attractive to coprophagous insects (tail-end). Comparisons were made between dung beetle distributions on rat carrion with carrion beetle (Coleoptera: Silphidae) distributions, a model of distribution patterns for a taxon known to target carrion. A total of 25,081 dung beetle individuals from 21 species and 3,333 individual carrion beetles from 9 species were collected in our year-long study. Results indicate that dung beetles show higher attraction to the head-end of rat carrion than the tail-end. This distribution pattern is also found in carrion beetles, suggesting that similar resources are being targeted. When dung beetles are grouped by behavioral guilds, rollers and tunnellers also share this pattern of greater abundance at the head-end rather than the tail-end, but dwellers show no discernable difference between the head- and tail-end. This research indicates that dung beetle interactions with carrion that are more complex than previously understood. Our results suggest that scarabaeine dung beetles target carrion preferentially, challenging the long-held belief that, within temperate regions, dung beetle necrophagy is rare and unimportant to the decomposition of carrion.