Why Are Moths Attracted to Light? What New Research Shows

The answer in short

For millions of years, the brightest part of a night-time view was the sky, lit by the moon, stars or the glow after dusk. Many flying insects use this to tell which way is up: they keep their dorsal side, their back, toward the light. This is called the dorsal light response, and it helps them fly level, especially when it is too dark to see the horizon clearly.

An artificial light breaks that rule. When a moth flies past a lamp, the “sky” is suddenly beside or even below it. As the moth turns its back toward the lamp, it banks and curves around it. Many insects end up orbiting the light, unable to break away, until they tire, land nearby or are eaten. This explains the old saying “like a moth to a flame” without the insect actually wanting to reach the light.

What the 2024 research found

The key study was published in Nature Communications in January 2024 by a team led by Samuel Fabian and Yash Sondhi. They filmed moths, dragonflies and other flying insects around lights with high-speed cameras in the laboratory and in the field in Costa Rica, and reconstructed their flight paths in three dimensions.

Instead of flying straight into the lights, insects showed three recurring patterns:

• Orbiting: circling the light, with the back held toward it.
• Stalling: pitching steeply upward near the light until they lost speed.
• Inverting: flipping upside down when passing over a light shining upward, often dropping toward the ground.

In each case, the insect’s back stayed tilted toward the light source. The researchers concluded that the dorsal light response explains why insects gather at lights better than earlier theories. A moth that wanders near a lamp is not choosing to go there; its own steering reflex holds it close.

Old theories: moon navigation, heat and more

Several older explanations have been popular for decades:

• Moon navigation: The best known theory said moths navigate by keeping the moon at a constant angle. Because the moon is so far away, the angle stays fixed in straight flight; with a nearby lamp, holding a fixed angle would make the moth spiral inward. The 2024 flight recordings found that insects rarely fly such spirals.
• Heat: Some people assumed moths seek the warmth of a flame or bulb. Yet insects gather around cool LED lights too, so heat cannot be the main reason.
• Escape toward the open sky: Another idea held that insects flee toward light because bright areas usually mean open sky and an escape route. This contains part of the truth, since light does signal “up”, but it does not explain the circling.
• Looking for darkness: One hypothesis proposed that moths are drawn to a darker band that the eye perceives beside a bright light. It has little support today.

Moths also do not mistake lamps for flowers. Many moths that come to lights, including the luna moth and the Atlas moth, have no working mouthparts as adults and never visit flowers at all.

Which lights attract the most moths?

Not all lights are equal. Insect eyes are especially sensitive to short wavelengths, so ultraviolet and blue light draw in the most moths. This is why scientists use mercury-vapor or ultraviolet lamps to survey moths, often shining them onto a white sheet, as in the photo above.

How strongly each species responds varies. Some moth families are seldom seen at lights, and in many species one sex arrives more often than the other. Weather matters too: warm, humid, cloudy nights without moonlight usually bring the most moths to lamps.

How artificial light at night harms moths

Light pollution is now considered one of the pressures on insect populations, alongside habitat loss, pesticides and climate change. Moths trapped at lights waste the short time they have for feeding and mating, burn energy and are easy prey for bats, birds and spiders.

The effects reach beyond individual moths. A study published in Science Advances in 2021 compared hedgerows and grass margins in southern England. Hedgerows lit by streetlights had nearly half as many moth caterpillars as unlit ones, and the effect was strongest under white LED lights. Lighting can also disrupt egg laying and feeding, and a Swiss field study published in 2017 found that flowers under streetlights received far fewer visits from night-flying pollinators.

Moths are an important food source for bats and many birds, so losses ripple through food webs. You can read more about bats as moth hunters in how many insects does a bat eat in a night?

How to reduce the impact of outdoor lights

The research points to simple, practical steps that help insects without leaving people in the dark:

• Switch off outdoor lights that are not needed, or use timers and motion sensors.
• Use shielded fixtures that point light down onto the ground where it is needed, not up into the sky or sideways into trees.
• Choose warm white, yellow or amber bulbs rather than cool white or bluish ones.
• Keep curtains drawn at night so indoor light does not spill into gardens.

These measures, recommended by dark-sky groups and conservation organizations, also help birds, bats, fireflies and other night-active animals. Fireflies are especially sensitive, because they rely on their own light signals; see are fireflies disappearing?