Spotlight

Glowworm Man

My name is Adam Broadley. I'm a 22-year-old postgraduate student at the Department of Ecology, Massey University. After completing my BSc I was on the lookout for a suitable topic for my Masters thesis. Creepy-crawlies had always fascinated me, especially the more unusual or secretive ones. Initially I considered studying Mystacinobiidae, a wingless fly found living on short-tailed bat guano, but as you can imagine, the prospect of climbing great heights into rotting trees and wading around in bat dung soon put that idea in its place!

I approached Ian Stringer, a keen entomologist in my department who suggested I research the behavioural ecology of one of the worlds most curious creatures -- the New Zealand glowworm Arachnocampa luminosa.

The glowworm is not a worm at all, but the larval stage of a tiny gnat. Glowmaggot would be a more accurate but less appealing appellation!

In the past, researchers had used artificial light sources to make basic behavioural observations of nocturnal or caverniculous (cave-dwelling) fauna, but artificial light has the unfortunate effect of disturbing them, and observations of bewildered fauna result in abberrated data. Recent technological advances in the field of night vision have opened up exciting new opportunities for ecologists.

Late in 1994, the department purchased several electronic components for night vision studies -- a time-lapse video recorder, a monitor and a closed-circuit TV camera. Unfortunately, electronics are well known for becoming temperamental when exposed to the wet, muddy environment common to most caves. We therefore constructed waterproof sheet-metal cases for the video and monitor, and a waterproof housing for the camera, which also helped protect fragile gear when accidentally bashed against obstructions. Staff in the Department of Production Technology helped construct infrared light sources with wavelengths invisible to the naked eye, but which are can be used by a videocamera sensitive to them.

To power the equipment in remote locations we had to find a battery with enough capacity to drive it for 24 hours. After much searching I bought two, large 85-amp hour deep-cycle batteries. I didn't reckon on their mass -- 20 kg each -- which would prove difficult to carry without the aid of a pack. So I built a pack out of plywood and had a friend at an equestrian supply store fit it with padding and straps.

Since fine-tuning the equipment I have filmed in several caves at Waitomo, and in the Ruakuri Scenic Bush Reserve nearby. I have 1,200 hours of glowworm larval, pupal and adult activity on videotape in both cave and bush environments. There is footage of larvae fighting each other, prey capture, glowworm nest construction, a glowworm attacking a spider many times its own size which had blundered into its nest, and glowworms defecating, as well as many other behavioural patterns.

Glowworms are eating machines, luring insects into sticky threads which dangle below the animal. They possess a strong pair of chitinous mandibles, capable of crunching through the tissues of most invertebrates. Larvae live for 9-11 months before pupating and hatching into adult flies, which live for 3-5 days. They cannot feed because they have reduced mouthparts.

I filmed a mating pair which copulated for 26 hours before being eaten by a large harvestman (with legs spanning the size of your palm, and noted for remaining absolutely motionless for days on end). In basic terms larvae eat for nine months, pupate then indulge in sex for most of their adult lives and then die!

Early in September I set the video equipment up in Reserve Cave -- a large dry cave infrequently visited by humans and noted for its large piles of scree and slabs of rock on the cave floor, resulting from ceiling collapses. The cave is dry only between the entrance and the streamway at the far end where glowworms abound. After spending hours setting up the equipment, the typically Waikato weather decided to enter its monsoon phase late in the afternoon and rained all night.

The next day I returned to the cave ready to swap batteries and found the entrance-way waist deep in water. Under the water the floor was composed of slippery clay, so that even when carefully negotiating my footsteps I managed to lose my balance and submerge myself. Thankfully I had left the battery outside the cave in its pack.

Soaking wet, angry and frustrated I slunk back to the Museum of Caves and talked to Pete Chandler, one of the operators of Black Water Rafting, who suggested I raft the equipment out in an inflatable dinghy, and the next day Tamsin Ward-Smith, a friend and colleague working on kiwis nearby at Otorohanga helped me move the equipment out.

My study of A. luminosa has not been without its share of trials and tribulations, but I count myself lucky as to be able to study this unusual creature in many unusual subterranean locations.

Adam Broadley

Adam Broadley