Patterns and mechanisms for larval aggregation in carrion beetle Necrodes littoralis (Coleoptera: Silphidae)

Carrion is a patchy, nutrient-rich and frequently bulky resource that hosts a complex community of competing organisms. Several insect species have specialized to use carrion for breeding, revealing a specific suite of behavioural adaptations. Larvae of carrion insects regularly aggregate while feeding, frequently forming spectacular larval masses. Here we analysed patterns and mechanisms of collective feeding by larvae of the communally breeding carrion beetle Necrodes littoralis. Using results of laboratory behavioural assays and findings from previous field experiments using pig carcasses we found that: (1) under field conditions N. littoralis larval aggregations were prevalent on large carcasses, during late decomposition stages; (2) under laboratory conditions larvae of all instars, when present on meat, formed stable aggregations; (3) larvae consistently responded to thermal characteristics of a feeding environment, aggregating in the hottest place and following changes in the heat source location, which suggests thermal cues are important for their aggregation; and (4) ground-deposited chemical cues elicited a minor response by the third-instar larvae, which indicates these cues are less important for the aggregation of larval N. littoralis. These findings highlight the prevalence of communal feeding among necrophagous insect larvae, revealing the interspecific and intraspecific diversity of patterns and mechanisms for larval aggregation on carrion.