Manifestation of Peaks in a Live Firefly Flash

Several studies have been carried out on flashing of fireflies till now. From patterns of its flashes in different ambient conditions, different conclusions have been drawn and hypotheses put forward. Here we observe flashes emitted by two Indian species of firefly Luciola praeusta and Asymmetricata circumdata. For the species L. praeusta, as the temperature is lowered below about 21 °C, simple pulses become compound or combination ones. Males begin to emit bi-modal flashes while females emit both bi- and tri-modal flashes, along with the simple ones, in a regular manner. For the species A. circumdata, this feature is evident even at their normal flashing temperatures. Though rare, three-peaked flashes do appear from male specimens of both these species, and decay times of all the three peaks in a male- or a female-flash come out to be a few tens of, or a hundred-odd, milliseconds - in contrast to the nanosecond lifetimes determined by different workers for different analogs of the light emitter molecule oxyluciferin. We propose that the tri-modal feature in a flash represents three luminescent forms of the excited state of oxyluciferin, which in the normal flashing state in the living firefly decays via a pathway followed by molecules exhibiting phosphorescence.