Regurgitation behaviour of the Lasius flavus worker (Formicidae) towards the myrmecophilous beetle Claviger testaceus (Pselaphidae) and other recipients

The regurgitation behaviour of the Lasius flavus worker towards the myrmecophilous beetle Claviger testaceus and other recipients is compared. Examination of the antennal and mandibular positions and of the dynamics of the functioning of the cephalic alimentary pump shows that the workers regurgitate their crop contents on the Claviger in the same manner as they do on insect cadavers, which are in a state to be given as solid food to the larvae. The workers regurgitate differently to ant larvae and, especially, to other workers, gynes and males. Concerning regurgitation, the workers thus handle the guest beetle as an insect cadaver. As they regurgitate in response to particular secretions of the Claviger, it may be inferred that the regurgitating allomone emitted by the beetle mimics the action of a substance produced by decaying insect corpses. The observation of the functioning of the cephalic alimentary pump shows that, in L. flavus, ‘regurgitation’ of ingluvial liquid on the Claviger or a cadaver comprises a few disgorging movements followed by numerous reingesting movements. When the receiver is an ant imago, regurgitation is more complex and characterized by rapid alternations of food fluxes and refluxes in the donor worker, during which process the ant constantly maintains a typically external donor posture. The function of the workers' regurgitation upon insect cadavers is discussed. It is hypothesized that this behaviour is instrumental in ensuring the extraoral enzymatic digestion of solid meaty food given to larvae or in providing them with a more balanced diet. Cannibalism in L. flavus is also discussed.