Dangling from the ceilings of New Zealand's Waitomo caves are nature's own Christmas lights.
Like thousands of fairy lights, they twinkle like stars, creating a spectacle for tourists.
But there is more than meets the eye.
These stars are actually sticky traps used by glow-worms to capture their prey.
The larva first constructs a tube of mucus.
Then it coughs up dozens of very fine silk strings - about a sixth the width of a human hair, and up to nearly 60cm long - and dangles them from the bottom of the tube.
It then regurgitates mucus onto the silk strings, which collects in tiny droplets that absorb water from the atmosphere and expand. The glue consists mainly of water and the rest is made up of protein, salt and urea - a chemical found in urine.
To attract mayflies, the glow-worm illuminates its net of reflective drops by turning on its bioluminescent tail and shuttling through the mucus tube.
Tourists entering the caves bring about a change in temperature, which results in a drop in humidity. In a study in the journal PLOS One, scientists reported that if humidity drops to below 80 per cent, the droplets will evaporate.
Without these sticky nets, the glow-worms cannot catch mayflies, leaving them to starve and their populations could eventually vanish.
Now, some caves have automatic door systems that prevent anyone going in until the humidity is back to normal.