In the bygone years in Hong Kong there was a time when I had to attend Japanese language class two evenings a week at the Japanese consulate. On the way to the consulate I always walked by a spot between City Hall and the HMS Tamar British Forces headquarters. It was there that for the first time I saw soaring specks of the light of fireflies, decorating the sky at dusk.

Recently I read an illustrated book by Ho Chien-jung on the fireflies in Taiwan. I came to know that there are about 2,000 species of fireflies in the world. Fireflies are beetles mostly less than an inch in length, two-third of which have the ability to emit light in all of the four stages of the egg, the larva, the pupa and the adult firefly. The light of the adult insect comes from the "lantern" -- technically known as the photophore -- located on the underside of the rear part of the abdomen. In the lantern, the chemical compound luciferin and the enzyme luciferase react with oxygen to produce light, which is directed and intensified by the reflector cells. The light thus produced has aroused people's interest in firefly-viewing (known as hotarugari in Japanese). The light functions mainly as a signal of attraction between the male and the female prior to mating. In greenish yellow, orange yellow or green, their light flashes across the evening sky. What a little wonder in mother nature.

Most firefly larvae measure less than half-an-inch. With an appearance resembling caterpillars or centipedes, the larvae are a little frightening. A two-part Cantonese allegorical saying says, "Chickens eating worms that glow." These glowing worms must doubtlessly be the larvae of fireflies. The larvae are carnivorous, and little land or freshwater snails -- usually pests -- are their favourites. The adult fireflies do not need food. At most they just consume dew droplets or pollens of flowers. Therefore, fireflies are human-friendly insects.

However, the living space of the fireflies is dwindling because of industrial pollution, overdose of agricultural chemicals, and the development of hilly areas and land bordering on streams. In view of this, conservation efforts have begun in places like Japan and Taiwan. Japan has even set up a national association for research on the fireflies. Let's hope that the firefly's light keeps on illuminating our evening sky, for years and years to come.