The Waitomo caves in New Zealand are famous for thousands of blue light dangling from the ceilings, giving the illusion of twinkling stars in the night sky. The caves are a common stop for tourists, who are often awe-struck by the beautiful starry night illusions all around them. But the science behind the natural wonder is what is truly remarkable about the caves.
The insects use bioluminescent light and silk threats covered in sticky, reflective droplets to attract and capture their prey, notes Janek von Byern, a zoologist from the University of Vienna who spent months in the two dark caves. Studies from his team help us understand the real mystery of the glow worms—down to the microscopic details.
For a century, scientists have called the glow worms Arachnocampa luminosa, after their spider-like silk traps and luminosity. But the glistening ‘webs’ you’ll spot in the caves have very little in common with the spider’s web.
“It’s functionally completely different—chemically—and structurally, also,” Dr. von Byren concludes.
So how do the webs work? It begins with a fungus gnat egg hatching and larva constructing a tube of mucus that can be up to a foot long. It then coughs up dozens of silk strings, about a sixth the width of a human hair, and dangles them from the bottom of the tube. It then regurgitates mucus onto the silks, collecting tiny droplets that absorb water from the humid atmosphere. The mucus is waste: protein, salt and urea—a chemical found in urine—combined into toxic wood glue.
To lure its victim, the glow worm illuminates a net of reflective drops by turning on its tail and shuttling through its mucus tube. Contrastingly, a spider’s web comes from glands in its abdomen, not waste in its mouth. The glow worm periodically checks its lines for mayflies. Each thread can hold about three mayflies before it breaks.
To test these threads, scientists had to remain inside of the caves, because when the strings were removed from the humidity (dropping below 80 pecent), the droplets disappeared. This is yet another difference between glow worm webs and spider webs.
“A typical spider glue will absorb water from the atmosphere even at normal, ambient humidities,” Todd Blackledge, a biologist who studies spider webs commented, “but these glow worms have to be in these damp, moist caves or their glues will dry out very, very quickly.”
Scientists believe the differences between spiders and glow worms go beyond habitat, but are also related to the origin of the web components.