What Makes a Glowworm Glow?
A glowworm uses its glow to attract food and to burn off its waste. Its tail glows because of bioluminescence, which is a reaction between the chemicals given off by the glowworm and the oxygen in the air. This chemical reaction produces light, which the glowworm can control by reducing the oxygen to the light organ.
Insects fly towards the light and get stuck in the sticky lines that the glowworm hangs down to catch food. Glowworms also use their glow to put other creatures off eating them.
The female glowworm is equipped with one of the most marvelous lighting systems in the world. A wingless beetle, she crawls about at night eating small insects. But on the lower side of her abdomen she possesses a “lantern” which she uses to signal to her winged mate flying above.
This “lantern” has a transparent layer of skin, like the lens of a lamp. Behind this is an oily layer of tissue which produces the light by a chemical process, and a second layer which acts as a reflector. The glowworm is able to control this remarkably bright light, using it only at certain times to attract a mate.
In fact, the light is a sex-call, and the male has particularly large eyes to enable him to see the signal. An abundant supply of water and oxygen is needed by the glowworm to maintain the chemical activity producing the light. For a time, even the insect’s eggs are luminous. Glowworms, which are about half an inch long, are natives of Europe.
Other beetles with built-in lighting systems are called fireflies. Both male and female fireflies have wings and use lanterns to signal to each other and to warn off night birds who seem to find them unpalatable. The most famous are the large and brilliant cucujos of tropical America. On special occasions young women fasten them to their dresses where they shine like glowing gems.
Glowworms can survive only in very damp, dark places where their light can be seen. They need a ceiling that is fairly much horizontal from which they can hang their sticky feeding lines, and a sheltered place where wind does not dry them out or tangle their lines. The Waitomo Glowworm Caves provide a perfect environment with an abundance of insects brought into the cave via the river.
The lifecycle of a Glowworm is in four stages and takes about 11 months. Eggs are laid in clutches of 30-40 on walls and ceilings. Immediately on hatching from the egg, the larvae emit a light; build a nest, put down lines and feed. Sticky substances on the lines trap insects and these are drawn up and devoured.
The larvae stage is the longest phase in the creature’s life and lasts around nine months. It then turns into a pupa in a cocoon and emerges as a two winged flying insect, which looks like a large mosquito.
The adult fly lives no longer than a few days as it has no digestive system and so cannot eat. Instead it uses this time to mate and lay eggs. The glowworm found in the Waitomo Glowworm Caves is a species unique to New Zealand.
The female fly lays around 120 small spherical eggs. Within around 20 days the young larvae hatch from the eggs and crawl away. After hatching the young larvae build a nest, put down lines and feed. Sticky substances on the feeding lines trap insects and these are drawn up and devoured.
Even at this small size, less than 3 millimeters long, they emit a strong visible light and slowly grow over 9 months to the shape and size of a matchstick.
The pupa is the same as the cocoon stage in the butterfly lifecycle; it is the stage between the larva and the adult fly. This will last about 13 days with the pupa suspended by a thread from the ceiling.
The adult glowworm looks like a large mosquito. They have no mouth and their only function is to reproduce and disperse the species. Usually a male is waiting for the female to emerge from the pupa, mating takes place immediately and the cycle continues. Adult glowworms live no longer than a few days.