Glowworms - New Zealand's rockstars

Glowworms. Bright blue-green dots. They attract food with light. There’s a lot of them in caves. They’re…a good tourist attraction? 

How much do you really know about glowworms?  

You’ve seen the mesmerising lights, you may be familiar with the shining chains covered in droplets – and you might think the chains are glowworms themselves. Buckle up; the real story, and their real appearance, is a whole lot stranger. 

Actual glowworms are something straight out of science fiction movies, or maybe a supernatural horror. It looks like an intestinal parasite, or bits of maggoty egg yolk encased in plastic wrap. The neon blue light we all know and love sits at the tip of a long, bumpy, limbless tube. It’s like a finger–a really long, thin, finger that belongs on a cursed ancient corpse, translucent enough to see things you wish you couldn’t and shining with its own secreted mucus. It’s hard to believe humans can live in the same terrain as something like this, much less call it beautiful.  

And if this ruins the fun, I can’t wait to tell you that glowworms are actually gnat larvae. 

Adult glowworms are just regular gnats. Credit: Steve Kerr / © Otago Museum / Wikimedia Commons / CC BY 4.0 

While glowworms do glow, the rest of the name isn’t all that accurate. They’re not worms at all, but the larval stage of a fungus gnat. Yes, those little irritating insects that land on your food–although you won’t need to worry about that with this species. We’ll get to that jaw-dropping tidbit later. Despite being classified as a fungus gnat–named for the genus’s general diet–glowworms are carnivorous and have nothing to do with fungus. Another strike for our naming conventions. Their Latin name, Arachnocampa luminosa, does no better. It means “luminous worm-like spider.” They’re really not spiders, either.  

Did we at least believe they were spiders, or worms, when we named them? Nope! We thought they were beetles. 

Until just before the 20th century, the English assumed glowworms were beetles. They were familiar with bioluminescence in insects such as fireflies or the British glow-worm (also not a worm), so they figured anything glowing on land had to be a beetle. This lasted until a chap named George Hudson ended up raising glowworm larvae to adulthood in a lab, proving once and for all that those odd lit-up tubes grew up to be little, tiny gnats. 

The Māori names for glowworms are much more accurate. Pūratoke, from the verb meaning ‘to glow,’ has all the cool benefits of naming a creature directly after glowing without the impropriety of calling it a worm. The name titiwai is even better–from titi, starlight, and wai, water, it describes the bright reflection of bioluminescence on the water below. 

Titiwai is an excellent descriptor, as they are always found in humid areas, often near bodies of still water. Glowworms require very specific conditions to maintain the beaded white silk chains I mentioned before–their own creations, measuring anywhere from half a metre to just a few centimetres long, depending on air currents. These chains are silk traps, just like spiders’, which they use to catch food. The shining beads are actually droplets of thick mucus, sticky enough to ensnare anything it touches.  

Hundreds of carnivorous gnat babies and their thick chains of mucus. Credit: ArtofVisuals, Creative Commons License.  

A glowworms’ light comes from a chemical reaction in the insect equivalent of a human kidney. They combine various enzymes with ATP and oxygen to set off a chemical reaction that causes light to form. This ‘kidney’ is encased within an air sac that both provides oxygen and concentrates the output of light. The glowworm is in full conscious control of this reaction, as they can control the flow of oxygen themselves. If they stop feeding oxygen into the kidney, the reaction will die down, and their light will shut off after a few minutes. Since it takes time, if there’s an immediate threat, the still-glowing glowworm wiggles into a rock crevice to hide.

Larvae with intense chemical reactions happening in their kidneys. Credit: John Hartanowicz, CC BY-SA 4.0, via Wikimedia Commons.  

Surprisingly, every individual glowworm coordinates their glow as a colony. They’ll measure the light output of their fellow larvae and adjust their own accordingly, to maximise how much they glow over certain periods. Dozens of glowworms working in tandem is far brighter than one, and much more likely to attract larger numbers of prey. They all light up together when their prey is most active, and rest when they don’t need to expend that energy.  

 

But after nine or so months, prey stops being a concern. Once glowworms metamorphose into adults, they lose the ability to eat–because an adult glowworm quite literally has no mouth. Mating is their priority, and food only serves as a distraction. They live off of stored energy, consuming what’s left of themselves for sustenance. 

 

But they don’t need to do that for long. Immediately after an adult female emerges from the pupa, she will mate, lay around 100 eggs, and then die. Males fly around for a few more days, desperately trying to mate with more females before they quickly drop dead from starvation. It’s hard to eat when you don’t have a mouth. 

 

Next time you’re enjoying those beautiful blue-green lights, remember you share the space with dozens of badly named mucus-covered finger-shaped gnats. Remember they coordinate with each other, and the spellbinding glow comes from an insect kidney filled with chemicals. But, whatever you do, don’t smile. You still have a mouth, and that’s just showing off.  

Youth Creature Feature is your monthly dose of Aotearoa New Zealand's wacky, whimsical, and wonderful native and endemic species. 

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