Luring Love Lights

Professor Dr. Friedrich Schaller of the Braunschweig Technische Hochschule's Zoological Institute is a scientific voyeur. He has spent the better part of the past three years spying on the love life of Germany's two native glowworms. The males of the Lampyris noctiluca family, he reports with apparent approval, are choosy in picking their mates. The males of Phausis splendidula are as undiscriminating as sailors home from the sea.

Both species are beetles whose larvae live in damp places and feed on snails. The adult females cannot fly. When they reach maturity, they wait patiently for dusk, then climb to a high spot and turn on their seductive light. Males flying overhead spot the beacon and drop down to pay court.

Belly Dance. Determined to find out just how the light lure works, Dr. Schaller made dummy females and lit them from inside with tiny electric bulbs. When the dummy's light duplicated the yellow-green of the live females, Lampyris males were attracted to the fake female as readily as to the real. Yellow light excited them even more, while red, green and blue light left them indifferent. Only an overanxious few were attracted by lights of the wrong size or shape.

When a Lampyris female does not find a mate promptly, says Dr. Schaller, she begins to wag her abdomen. As time passes, her little belly dance becomes more frantic. Dr. Schaller rigged his dummies for vigorous wagging, and they had outstanding success in attracting mates. Lampyris noctiluca, he is convinced, has a highly selective optical system for locating willing females.

Fickle Failing. Phausis splendidula males are made of far less discriminating stuff. Besides mating properly with Phausis females, they go for almost anything that shows a light. They have been known to try unsuccessfully for hours to mate with Lampyris females. They respond to dummies with lights that are unnatural red or blue, and they seem to prefer a dummy with a lure that is bigger or brighter than normal. Phausis females, also, are less resourceful than their Lampyris relatives. No matter how long they go unmated, they never wiggle their abdomens. Dr. Schaller believes that such Phausis dullness keeps the sexes from getting together. As a kind of compensation for this biological disadvantage, there are five blundering Phausis males for each female, while the efficient Lampyris male-to-female ratio is one to one.

One odd failing common to both species is extreme male fickleness. As soon as actual mating begins, the female turns off her light lure. But if another female is in the vicinity with her light still glowing, the busy male is as likely as not to disengage and hasten to the shining new partner.

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