The Bioluminescent Hunter
The famous glowworm of Waitomo is not a worm at all. It is the larval stage of a fungus gnat, Arachnocampa luminosa, a species found only in New Zealand. The name Arachnocampa luminosa translates to "glowing spider-larva," which accurately describes its method of capturing food. The larva, which can grow up to 40 mm long, spends 6 to 9 months in this stage. It builds a nest of silk and mucus on the cave ceiling and then suspends up to 70 sticky silk threads below it. These "fishing lines" trap small flying insects, such as midges, that are attracted to the larva's light. When prey becomes entangled, the larva pulls up the thread and consumes its meal.
The light comes from of a chemical reaction. A specific enzyme, luciferase, acts upon a compound called luciferin in the presence of oxygen and an energy-providing molecule. This reaction, which occurs in the larva's modified excretory organs (Malpighian tubules), produces a blue-green light with a maximum wavelength of 487 nm. The intensity of the glow is directly related to the larva's hunger; a hungrier larva shines more brightly to attract more prey. Once it has fed, its light dims. After its long larval stage, it enters a pupal phase for about two weeks before emerging as an adult fly. The adult gnat has no mouthparts and cannot eat; its sole purpose is to mate and lay eggs during its short life of just a few days.