The common name “glow worm” refers to a creature that lights up dark, damp environments such as caves, abandoned tunnels, and sheltered forest banks. These shimmering displays are a sign of highly specialized predatory behavior. The blue-green bioluminescence, which creates the effect of a starry night sky, is directly linked to the animal’s survival and its unique method of catching food.
Identification and Life Stage Diet
The creature commonly called a glow worm is not a worm at all, but the larval stage of an insect. In New Zealand and Australia, the famous cave-dwelling glow worms are the larvae of a carnivorous fungus gnat, scientifically known as Arachnocampa luminosa. In contrast, the glow worm found in Europe, Lampyris noctiluca, is the larva of a beetle, and its diet and hunting method are entirely different.
The larval stage is the only time the fungus gnat glow worm feeds, which can last for many months up to a year. The adult insect that emerges is a delicate, short-lived fly that does not possess functional mouthparts. This adult form focuses solely on reproduction, meaning the larva must consume enough food to sustain the insect through its entire non-feeding adult phase.
Primary Prey and Food Sources
The diet of the New Zealand and Australian glow worm, Arachnocampa luminosa, consists mainly of small flying insects. These larvae are carnivorous predators whose preferred meals are tiny, soft-bodied creatures such as midges, mosquitoes, and small flies. They also trap larger insects like caddisflies and small moths, which are attracted to the light.
Glow worms are not restricted to flying prey. Non-flying invertebrates, including spiders and even cannibalized glow worm larvae, can become part of their diet.
The Lure and the Trap: Hunting Mechanisms
The glow worm’s hunting strategy relies on two interconnected components: a bioluminescent lure and a sticky silk trap. The blue-green glow is a product of a chemical reaction involving a compound called luciferin and an enzyme called luciferase, which combine with oxygen to generate light. This glow is emitted from an organ located at the posterior end of the larva’s body.
The light attracts prey through a phenomenon called positive phototaxis, where flying insects instinctively move toward the brightest point in the dark. Below the larva, a dense curtain of fine, vertical threads, or snares, hangs down, which the larva constructs from silk and mucus. Each strand is studded with droplets of a highly adhesive, thick mucus, acting like beads on a necklace.
A single larva can suspend up to 70 of these lines, which range from a few centimeters to half a meter long, depending on the environment. When a flying insect is drawn to the light and collides with one of the sticky droplets, it becomes instantly trapped. The larva senses the struggle and quickly reels in the thread by consuming the silk line until the immobilized prey reaches its mandibles for consumption.