Tiny Light-Bearers of New Zealand
BY AWAKE! CORRESPONDENT IN NEW ZEALAND
THE night was intensely dark—moonless and clear. When the camp lights went out, we seemed to be in a universe of bright stars. We made our way down a steep path to a thermal pool at the bottom of a narrow gorge. Plants were growing on either side of the steaming water. We sank into the water and relaxed after a long day of travel. This pool, with hot water bubbling out of the ground naturally, was at our overnight accommodations at a motor camp.
I watched as a star moved rapidly across the sky. I turned to tell my wife about it, and as I did, I stumbled and splashed loudly. To my amazement, several stars suddenly went out—vanished! And when I spoke in surprise, a whole cluster disappeared. I seemed to have caused a hole in the universe!
As I tried to figure out what had happened, the stars reappeared, one by one, and I now saw that one cluster was much closer to me than the main body of stars. In fact, some were close enough to touch. We had met New Zealand glowworms for the first time. They were suspended from the invisible walls of greenery above us, and their soft lights blended into the starry background.
The New Zealand glowworm is not a worm but an insect. It is different from glowworms and fireflies in other parts of the world. Its name Arachnocampa luminosa might give you the idea that it is a kind of luminous spider. But that is not true either.
Not long after our first encounter, we met glowworms again, at the Waitomo Caves on the North Island of New Zealand. Let me describe our journey to the glowworm grotto, where a boat took us to see these tiny creatures.
The Glowworm Cave is a wonder, beautifully lit to show the magnificent artistry of stalactite and stalagmite formations, which have built up over many thousands of years. Our guide turned on lights as we approached each area, and we were amazed at the fascinating formations and tunnels—an unexpected and strange world of marvels under the ground. Our footsteps echoed eerily when we gathered at the top of stairs that descended into blackness. As our eyes became accustomed to the dark, we began to see tiny glimmers of greenish light high up. The glowworms!
We reached a jetty and got into a boat. Moving away from the jetty, we sailed into darkness. Then, as we rounded a corner, what I can only describe as a compressed version of the entire Milky Way appeared just above us—the roof of the cave was completely covered with glowworms. Author George Bernard Shaw called this place “the eighth wonder of the world.”
The Fascinating Glowworm
When the tour ended, our wonder over the glowworm encouraged us to learn more about it. And what we learned was as fascinating as what we had seen. Starting life as a tiny larva, with tail light already switched on, the New Zealand glowworm builds a hammock of mucus and silk from separate glands in its mouth and attaches it to the ceiling of a grotto. The hammock is actually a tunnel in which the larva can move back and forth.
The glowworm needs food to live, so for six to nine months, it takes up fishing. But its catch is in the air, though it comes via the water. The essential stream brings in a supply of midges, mosquitoes, stone flies, and mayflies, which are attracted to light. To catch them, the glowworm lets down a series of silken lines (sometimes as many as 70) from its hammock. Spaced evenly down each line is a series of sticky droplets of mucus, so the lines resemble tiny pearl necklaces hanging straight down.
The most fascinating part of the glowworm is the light with which it illuminates the fishing lines. The New Zealand glowworm is one of a group of insects whose glow is not connected to the nervous system. Yet, it is able to turn the light off at will. The light organ is housed at the end of its excretory tubes, and part of the larva’s breathing system acts as a reflector, sending the light downward. It turns the light off by restricting the oxygen or the chemicals needed to produce the light.
However, the light at the end of the glowworm tunnel is not the hopeful sign an insect expects. It flies into the deadly curtain where a chemical may, it has been suggested, gradually anesthetize it. Sensing the vibrations of the struggling victim, the larva hangs precariously out of the hammock and hauls up the line in its mouth, using contractions of its body.
Having fished and fed for six to nine months, the larva pupates and then enjoys life as an adult. Whether the adult fly actually enjoys life much is doubtful. It will last only two or three days, for the adult fly has no mouth and so cannot eat. Its remaining time is devoted to reproduction. Adult male flies fertilize females the moment they break out of their cocoons. The female may take an entire day to lay her eggs, one by one, after which she dies. Having contributed to a sparkling galaxy that gives immense pleasure to humans, the 10- to 11-month life cycle of the tiny New Zealand light-bearer is over.
[Picture on page 16]
Opposite page: Entering the glowworm grotto
[Picture on page 17]
Top: The grotto roof with light show by glowworms
[Picture on page 17]
Right: Glowworm fishing lines
[Picture Credit Line on page 16]
Pictures on pages 16-17: Waitomo Caves Museum Society Inc.