Larval juice anyone? The unusual behaviour and morphology of an ant nest beetle larva (Coleoptera: Carabidae: Paussini) from Thailand

The third instar larva of Paussus siamensis Maruyama, 2016 (Coleoptera, Carabidae, Paussini) from Thailand, belonging to the Paussus hystrix group (sensu Maruyama, 2016), is described and illustrated by using both light and scanning electron (SEM) microscopy. Unlike other Paussus larvae, this larva was found inside a self-dug hole, in a nest of Pheidole plagiaria ants. Behavioural observations, documented by pictures taken in the field, show a peculiar strategy of P. siamensis larva to exudate big drops of transparent liquid from the thorax, promptly sucked by worker host ants. Behaviour of Paussus larvae is still unknown, but, due to their structural homogeneity, we suspect that digging and supplying attractive substances can be widespread within this genus. The similarity between P. siamensis and P. kannegieteri larvae, both Indo-Malayan species and guests of the same ant, is in agreement with their recent placement in the subgenus Scaphipaussus Fowler (sensu Robertson & Moore, 2016).