From coprophagy to predation: a dung beetle that kills millipedes

Abstract

The dung beetle subfamily Scarabaeinae is a cosmopolitan group of insects that feed primarily on dung. We describe the first case of an obligate predatory dung beetle and contrast its behaviour and morphology with those of its coprophagous sympatric congeners. Deltochilum valgum Burmeister killed and consumed millipedes in lowland rainforest in Peru. Ancestral ball-rolling behaviour shared by other canthonine species is abandoned, and the head, hind tibiae and pygidium of D. valgum are modified for novel functions during millipede predation. Millipedes were killed by disarticulation, often through decapitation, using the clypeus as a lever. Beetles killed millipedes much larger than themselves. In pitfall traps, D. valgum was attracted exclusively to millipedes, and preferred injured over uninjured millipedes. Morphological similarities placing D. valgum in the same subgenus with nonpredatory dung-feeding species suggest a major and potentially rapid behavioural shift from coprophagy to predation. Ecological transitions enabling the exploitation of dramatically atypical niches, which may be more likely to occur when competition is intense, may help explain the evolution of novel ecological guilds and the diversification of exceptionally species-rich groups such as insects.

Escarabeíneos copro-necrófagos (Coleoptera, Scarabaeidae, Scarabaeinae) de fragmentos de Mata Atlântica em Silveira Martins, Rio Grande do Sul, Brasil

“…Por outro lado, a proporção de tribos, gêneros e espécies capturada com armadilhas iscadas restringe-se apenas à maior parte da fauna de Scarabaeinae, uma vez que vários outros grupos de espécies geralmente não são atraídos por este método de amostragem (e.g. vaz- de-mello et al, 1998;vaz-de-mello, 2007;larseN et al, 2009;vaz-de-mello & GéNier, 2009). Dessa forma, a interação entre a diversidade dos grupos no neotrópico e a utilização de iscas compatíveis com o hábito alimentar da maioria das espécies parece refletir o padrão encontrado entre diferentes estudos que utilizam iscas para a captura de escarabeíneos.…”

Nutrient acquisition across a dietary shift: fruit feeding butterflies crave amino acids, nectivores seek salt

“…Drastic ecological, behavioral and morphological changes are associated with dietary shifts (e.g., Larsen et al 2009), but the consequences for life history and nutrient preferences are less well known. Here we ask how dietary shifts affect nutrient acceptance as one means to understand how such shifts lead to a changing landscape of nutrient limitation.…”

When attempts at robbing prey turn fatal

“…Second, Trigona, although of the same size as the smallest wasps, were comparatively good at escaping; nonetheless, 17.8 % of them were captured (Dejean et al 2012; Table 1). Third, dung beetles, which were not recorded as trying to rob prey from Allomerus ants, can be attracted to flesh (see Ururahy-Rodrigues et al 2008); only one species is predatory and is specialized in the capture of millipedes (Larsen et al 2009). …”