Glow worms are not really worms, but are actually the larvae of an insect known as the fungus gnat. Not to be confused with European fire flies, also called glow worms, the fungus gnat larvae are found in grottoes, caves, and other sheltered places in Australia and New Zealand. These larvae are major attractions in both these countries and bring in millions of dollars for the tourism industry every year. Their rising popularity among locals and tourists alike is not surprising given their interesting background.
Glow worms derive their name from their ability to produce light naturally, a process known as bioluminiscence. Their blue-green glow of light is emitted as a result of a chemical reaction between several components: a waste product called luciferin, the enzyme luciferase, an energy molecule called adenosine triphosphate (ATP), and oxygen. The light is used to attract prey such as small snails, midges, caddis flies, mosquitoes, mayflies, moths, and millipedes. In adult females, the light glows as a mating call to adult males nearby.
Depending on the surrounding environment and food supply, these insects have a life cycle lasting between 11 and 12 months. There are four stages in the life cycle:
Eggs. Female adult glow worms lay an average of 130 eggs. These eggs are laid in clusters of 30 to 40 in protected areas such as cracks and crevices. They are cream-colored, about 0.03 inches (0.75 mm) in diameter and very sticky, enabling them to stick to the cave walls and ceilings. As the eggs age, their color becomes darker. It takes three weeks for the eggs to hatch into larvae.
Larvae. Glow worms spend eight to nine months in this stage, the longest compared to the other stages of life. The larva begins to glow as soon as it emerges from the egg. It starts at a length of 0.12 to 0.2 inches (3 to 5 mm) and can grow up to 1.2 inches (3 cm) before pupating.
Glow worms build nests, impressive and organized horizontal tunnels of mucus and silk, from which hang 10 to 70 threads of silk fishing lines measuring between 0.79 to to 3.94 inches (20 to 100 mm). Due to the flexibility of their bodies, they can extend themselves to the length of the unmade fishing line and spit out mucus and silk as they move upward to form the line. These threads are covered in sticky drops of mucus that paralyze prey.
Glow worms live within these lines once they are complete. They move up and down the lines, glowing brightly to attract and ensnare prey. The hungrier they are, the brighter they glow. The worms can feel the vibrations when prey are trapped and immobilized by the drops of mucus. They glide towards the prey and consume it either by sucking out its juices or by eating it whole. Once the worms have had their fill of food, they stop emitting light.
Pupae. At the end of the larval stage, glow worms excrete a tremendous amount of mucus around their bodies. This mucus will eventually dry out and shrink, forming the pupal casing. Prior to this, the threads of fishing lines are arranged to form a protective barrier within which the pupal casing hangs safely.
While pupating, these insects emit light intermittently. As the pupal casing is transparent, the glow emitted attracts nearby adult males. This stage lasts around 12 days. Towards the end, female pupae glow brighter, signaling their preparation for mating.
Adults. The adults look similar to mosquitoes, with an average length of 0.59 inches (15 mm). They have a short lifespan, as they do not have mouths or any other means of feeding. In fact, their main goals are mating and reproduction. Adult males live between three to five days, while females live only a day or two, dying soon after laying their eggs.