Reflex-bleeding in the Firefly Pyrocoelia pectoralis (Coleoptera: Lampyridae): Morphological Basis and Possible Function

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Male adults of the firefly Pyrocoelia pectoralis discharge fluids from along elytral and pronotal margins and around the antennal sockets, but females when tactually stimulated only discharge fluids from pronotal margins and antennal sockets. Both genders, when disturbed, may also occasionally discharge fluid from the anus. With regard to its content of haemocytes and proteins, the discharged fluid conforms to haemolymph. A series of circular, but irregularly spaced depressions in the insect's cuticle along the pronotal and elytral margins seems to be related to the ‘reflex-bleeding’ response. Each depression features a centrally-placed columnar structure, which is connected to its surroundings by a thin membrane that easily ruptures and, once broken, initiates reflex-bleeding. The whitish and viscous blood oozing out is very effective in repelling ants. Reflex-bleeding in the adults of Pyrocoelia pectoralis seems associated with thanatosis and luminescence and, thus, supports other defense reactions that the beetle has at its disposal.