New Zealand is famous for remarkable caves like this one. Twinkling blue lights dangle from the ceiling, creating what looks like a starry night sky. The lights are made by glowworms.

    Each year, these caves attract many adventurous visitors—and it’s easy to see why. The lights are an incredible sight.

    But the glowworms’ glow isn’t just a pretty light show. It’s part of a death trap.

    Here’s how it works: First, the glowworm makes a tube of snot-like goo. Then it spits up a bunch of silky threads and hangs them from the tube. If you think that’s gross, wait until you hear what happens next. On each thread, the glowworm coughs up a considerable amount of sticky mucus. It places the mucus in drops, like beads on a string. 

    When glowworms are hungry, they light up. Other bugs are drawn to the light of the luminous glowworms. They fly upward and get stuck in the goo. Then along comes the glowworm to gobble them up. Yum!

    Glowworms may look like clear gummy worms, but they aren’t really worms. They’re the larvae of an insect called the fungus gnat.

    There are four stages in the life cycle of the fungus gnat. First comes the egg stage, which lasts about three weeks. When the egg hatches, out comes the larva, or glowworm. For the next six to nine months, the ravenous glowworm eats enormous amounts of food.

    Then the pupal stage starts, and the glowworm becomes a gnat. By then, the days of snot strings are over. The gnats have no mouths and never eat. They live for only about two days—just long enough to mate and lay eggs.