Glowworms (Arachnocampa luminosa) are found all over New Zealand, mostly in caves but also on overhanging banks in the bush where in dark and damp conditions you’ll often see the telltale bluey-green glow. A glowworm isn’t a worm at all, but the matchstick-sized larval stage of the fungus gnat (a relative of the mosquito), which attaches itself to the cave roof and produces around twenty or thirty mucus-and-silk threads or “fishing lines”, which hang down a few centimetres. Drawn by the highly efficient chemical light, midges and flying insects get ensnared in the threads and the glowworm draws in the line to eat them.
The six- to nine-month larval stage is the only time in the glowworm life cycle that it can eat, so it needs to store energy for the two-week pupal stage when it transforms into the adult gnat that has no mouthparts. The gnat only lives a couple of days, during which time the female has to frantically find a mate in the dark caves (the glow is a big help here) and lay her batch of a hundred or so eggs. After a two- to three-week incubation, they hatch into glowworms and the process begins anew.