What insect's larvae glow in the caves of New Zealand?

The insect whose larvae glow in New Zealand’s caves is Arachnocampa luminosa. It is a fungus gnat endemic to New Zealand, commonly called the New Zealand glowworm—not a beetle, firefly, or worm.

Its luminous larva produces a blue-green glow that attracts small flying prey toward sticky silk threads hanging from a cave ceiling. The larva builds a silk nest and suspends numerous snare lines dotted with adhesive droplets. When an insect becomes trapped, the glowworm pulls the thread upward and feeds on it.

The species is especially famous in the Waitomo Glowworm Cave, where thousands of larvae create a star-like display above underground streams. The larval stage can last up to about a year, while the adult is short-lived and cannot feed. The name “glowworm” is therefore a common-name trap: Arachnocampa luminosa is a fly relative, not a true worm or firefly larva.