The glowworms of Waitomo Caves fame are not worms. They are actually the larval stage of a species of “fungus gnats”. Fungus gnats usually feed on fungus, but this species (arachnocampa luminosa) is a predator. The “glowing spider-worm” larva is bioluminescent to attract flying bugs. It clings to something near/above water, extrudes web strings off itself, and then covers the strings with sticky droplets. In the dark, the Waitomo Cave’s roof looks like a wondrous fantasy world of will-o’-the-wisp snow. If you shine a light on the roof, it is a horror show of spider-worm snot.