In the Waitomo region of New Zealand, there is an underground labrynth of caves that have been forming over the last 30 million years. And in one of these caverns is a very special animal -- one that has evolved to thrive in wind-free places exactly like these caverns. The species is Arachnocampa luminosa, a species of fungus gnat that is luminous during the larval stage. When a person travels by boat or inner tube through the pitch black Glowworm Grotto, as the cavern is called, the ceiling looks like a galaxy of blue stars.
The glowworms, as they are commonly known, can grow to be about 3 centimeters long. When it hatches from its egg, the larva uses an interesting feeding strategy. It creates a nest of silk on the ceiling of the cave, and then drops dozens of long strands of mucus-coated silk down from the ceiling surrounding its nest. It will then hang out on the ceiling and glow, which attracts prey to its sticky strands of silk. When prey -- such as midges, moths, and other small insects -- are caught, the glowworm pulls the silk strand up and dines.
The larval stage lasts between 6-12 months, depending on food supply, and at this point the glowworm will pupate to an adult fly. Adult flies cannot eat -- their only task is to mate, lay eggs, and die. Thus, the glowing larval stage is the longest period of an Arachnocampa luminosa's life.
The larvae are sensitive to any disturbance, and will stop glowing if frightened. So visitors wanting to witness this glowing phenomenon need to be very quiet. Indeed, the largest danger to the species is not predation but human interference. Despite this, the glowworms seem to be doing well even with the many guided tours that have been bringing visitors to see the mock-galaxy they create along the ceiling of the cave for decades. Above is an image from a tour back in 1977. The species has even been featured in BBC's Planet Earth.
Check out this video that gives details and really cool images on this mind-blowing species. Skip to 2:25 to get to the specifics about the glowworms, but watch the whole thing if you'd like to know more about the caves in general.