Glowworms glowing in a cave

Joseph Michael

Glowworms harness a surprising ingredient to keep their threads sticky

This isn’t a photo of the Milky Way; it’s a deep, dark cave in New Zealand. And those blue things aren’t stars; they’re maggots. A chemical reaction in their Malpighian tubules—structures analogous to kidneys—makes their posteriors glow, much to the delight of more than 200,000 tourists who visit them every year. These larvae of fungus gnats eat by creating a hammock of mucus and silk secreted from glands in their mouth, and then dropping down fishing lines with glistening droplets that capture insect prey summoned by their glow. To find out what makes these threads so sticky, researchers went spelunking and brought threads preserved in liquid nitrogen back to the lab. They discovered glowworm threads have little in common with sticky spider threads. Spider silk is an incredibly complex mixture of silk and glycoproteins; the droplets on glowworm silken threads are 99% water, with just one unexpected ingredient: urea, the main component of urine, the team reports today in PLOS ONE. One question that remains is how the mucus threads, secreted at the head end of the larva, somehow become covered with small amounts of urea, which is produced at the other end. The researchers speculate that urea, which is used commercially as a glue in plywood and other laminates, might be the source of the stick in the silken threads. They’re keen to head back into the caves to find out.