National Geographic : 1971 Jul
Backlighted by evening's afterglow, a male Pteroptyx malaccae records dis tinctive double flashes in this time exposure as it leaves the mangrove. The twin blips, only 1/30th of a second apart, appear to the eye as single bursts. Dr. Ivan Polunin of the University of Singapore, who made this photograph, has discovered that all males of this' species conform to the same pattern. An oscilloscope in Dr. Polunin's laboratory (below) records the beetles' signals. The first of the twin flashes shows as a short upside-down "peak"; the second, brighter flash as a long one. Nearly a second elapses before the cycle repeats. Crisp outlines of the flashes testify to the insects' uncanny precision. Like all fireflies, Pteroptyx are adults of a wormlike larva, probably similar to this Malaysian glowworm (bottom right). Flashing only at night, they shun the limelight by day, seeking shade on the undersides of leaves (bottom).