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Bugs and Light: Why Moths Fly into Lights and Why Fireflies Glow

© Debbie St. Germain

Many insects are attracted to light, and some fly right into the light itself. Moths commonly hover around lights and are active at night. This attraction to light is a response called phototaxis.

When insects fly at night they use light sources such as the moon for navigation. Light from a distant source reaches both eyes with the same intensity. This enables the insect to fly in a straight line with both wings beating at the same rate.

If the light is from a closer source such as a candle or lantern, it changes the insect's perception. The light is perceived stronger in one eye than in the other eye. This causes the wing on one side to move faster. The insect then approaches the light in a spiral path, eventually drawing it into the light itself.

One good way to know if an insect is nocturnal is to look at their antennae. Insects with poor eyesight have longer antennae. Many varieties of beetles have poor eyesight. They use their antennae to move around safely at night. 

Why Fireflies Glow

Fireflies are actually beetles that use light to attract others in its own species. They recognize and respond to each other by the type of flash patterns they make. The light comes from a large transparent cell on their tails, and is produces when the chemicals luciferan and luciferase come in contact with oxygen.

The light, called bioluminescence, does not produce heat. Scientists are using the chemical found in fireflies and applying it to food science. If the food contains bacteria, it will glow. The larva and pupa also glow. They are commonly called glowworms in many parts of the world.

In New Zealand people visit caves where they can see glow worms hanging from the walls. Glow worms are a larval stage of an insect called the fungal gnat. They use their light to attract other insects, which they feed on, and the hungrier the worm is, the more its light will shine.

The copyright of the article Bugs and Light: Why Moths Fly into Lights and Why Fireflies Glow in Science for Kids is owned by Mary M. Alward. Permission to republish Bugs and Light: Why Moths Fly into Lights and Why Fireflies Glow in print or online must be granted by the author in writing.