These wonderful yet strange creatures are called arachnocampa luminosa. They're native to a northern part of the country called North Island.
Auckland photographer Joseph Michael documented the awe-striking creatures, which live in caves said to be as ancient as 30 million years old, by spending countless hours in the caves' ice-cold water.
Glowworms are actually the larvae of the fungus gnat, a type of fly that resembles a mosquito.
The glowworms are found only in New Zealand and eastern Australia. The Australian worms have smaller lights and tend to stay in smaller groups.
The first part of the species' name, Arachnocampa, means "spider worm," and refers to the web of silk threads the worms use to snatch their prey.
The roofs of caves make great homes for the larvae, which often reside side-by-side in groups of hundreds, because of their damp, sheltered surface.
The worms' glowing light helps them attract their food — other insects.
Many other animals are also bioluminescent, meaning they make light. The trait, which can be used to fend off predators, snatch prey, and lure mates is so useful that it's evolved independently at least 40 times. Most bioluminescent creatures live in the ocean, where their glimmers are often the sole source of light.
If light makes its way into the cave, the glowworms are rendered invisible to the human eye.
The insects are active at night. Many observers have described the experience of visiting the glowworms at night as similar to being under the stars on a clear night.
If the insects feel interrupted, they can switch off their bioluminescence. In the presence of torchlight, smoke, or insect repellent, for example,
they have been known to temporarily go dark, typically for as long as 15 minutes at a time.
The glowworms' beauty is fleeting: They live just long enough to mate and lay eggs.
The eggs hatch into larvae and then pupate into adult flies. Glowworms spend most of their life as larvae, however: between 6 and 12 months, depending on how much food is available.
The larvae are entirely soft except the head capsule, and when they outgrow this portion of their shell they moult, shedding their skin. This happens repeatedly during their lifecycle.
At the end of the larva stage, the insect turns into a pupa and hangs from the cave roof on a short thread for about 1-2 weeks, glowing intermittently. While the male pupae get progressively dimmer, the female pupae get progressively brighter.
Adult glowworms don't fly well. As a result, they often stick to the same geological area, building colonies.
Female glowworms lay roughly 130 eggs and die soon afterwards. About 3 weeks later, the eggs hatch and the cycle repeats.