Optics kit analyses signalling between fireflies

17 Jun 2002

LEDs and sensitive optical detectors are unravelling the secrets of firefly mating rituals. The signalling system of Photinus pyralis, the most common firefly in the US, has been quantified by James Case and his co-workers at the University of California, Santa Barbara. The researchers measure the flash intensities from fireflies with an integrating sphere photometer and study their communication behaviour during flight. They glue a male to a finely balanced direction-recording pivot and monitor his responses to light pulses from a green LED array that imitate female flashes. The male makes single 0.3 s flashes every 7 s during flight in search for a female. Each flash is accompanied by an upwards swoop, so that his signal looks like a luminous J. On seeing a properly shaped and timed LED flash, he turns and redirects his flashes.

The work is investigating preferences for sources of different brightness, discrimination among multiple sources, optical noise and directional memory. Case told delegates at the 10th International Symposium on Bioluminescence and Chemiluminescence in Bologna that the apparatus offers a simple means of investigating the firefly's nervous system and its ability to perform complex tasks. "Together with the well known bat sonar, the packaging of such systems in the brains of tiny animals must be the envy of instrumentation designers," he said.