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Hank brings you the tale of another weird place on earth - the Waitomo Caves of New Zealand, where glowworms emit bluish-green light in a beautiful display.

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[intro plays]

Bioluminescence is definitely one of the coolest things in nature, and I'm not disparaging any of the other wonders of the natural world, but the emission of light by a living thing... it's so cool! And although there are lots of bioluminescent organisms in the world — from angler fish to fungi, to cone jellies — one of the coolest places to see bioluminescence in action is in the Waitomo Caves, on New Zealand's north island. 

The caves are pretty normal, as caves go, until you get down in there and you realize the walls and the ceiling are glowing blue. And you feel kind of like they shouldn't be, but they are, right! Like, does anyone else on this cave boat think that the cave walls are glowing!? Well, it probably wouldn't happen exactly that way, because you probably wouldn't be down there if you didn't already know about the glowing thing before you got there, but they might not have told you the coolest part: why the cave is glowing.

Turns out, it has to do with the New Zealand fungus gnat, Arachnocampa luminosa, which is actually not very interesting in its adult stage, but, as larvae, they light up the Waitomo caves like Pink Floyd night at the planetarium. Before their very short, mouthless lives as an adult, mosquito-sized gnat, A. luminosa spends months as carnivorous larvae commonly known as glowworms. These larvae can get about as long as a match, and are pretty boring-looking in the light of day, but in the dark, a bluish-green light glows through their transparent skin.

Their bioluminescence is a product of a chemical reaction in a special organ in their butts, where oxygen, adenosine triphosphate, and a waste product, called luciferin, combine to make light. This bioluminescence is used to attract food and mates. The glowworms can live between 6 and 12 months on the walls of caves or other sheltered areas, usually over water. And the reason why they live in such dark, precarious places is that the New Zealand fungus gnat larvae are great hunters.

They hang out on the cave ceiling, in the dark, and suspend a fishing line made of silk, covered with globs of sticky mucus. They use their bioluminescence to attract insects to their traps, and then, bam! The prey gets all tangled up in their goopy lines, and they reel 'em in, paralyze them, and gobble 'em up. Since the adults don't have mouths, the larvae have to eat enough to keep the adult live during mating, so they'll eat pretty much whatever wanders into their net, even other glowworms. 

It's this cutthroat, cannibalistic struggle for survival that makes the Waitomo caves so beautiful to visit. Ain't that always the way?

 Closing notes

Thank you for watching this episode of SciShow. If you have any questions, comments, or suggestions for other weird places we should talk about, you can find us on Facebook and Twitter, or in the comments below. And, if you want to keep getting smarter with us, you can go to and subscribe.