A stream flows through the Waitomo caves. As visitors paddle, they look up at what seem to be stars in a pitch-black night. But they aren’t stars. They’re bioluminescent glowworms—the hungry larvae of small flies living near the cavern roof. Their steady light lures prey into the long, sticky traps the larvae have hung from the cave ceiling.
Glowworms living on the roof of the Waitomo Caves drop sticky threads from their bioluminescent tails, which glow brighter when the larva is hungry. When aquatic insects hatch from the stream below, they fly toward the light and become tangled in this line. Like an angler feeling a tug, the glowworm reels in and eats its catch.
The larva’s “fishing lines,” mucus threads studded with adhesive droplets, hang from a horizontal “runway” fixed to the cave wall with a kind of glue secreted by the glowworm. The runway functions as the larva’s home base; the animal can slide easily from end to end in order to drop lines or reel in prey. Glowworms maintain even spacing on the cave ceiling. That’s because a glowworm will attack and eat another larva that tries to set up shop too close.