It’s that time of year again when it’s finally warm enough to enjoy evenings outside in the great outdoors. Unfortunately, it’s also the time of year that our pesky insect friends have decided to rejoin us. They can prove to be particularly annoying when you’re sitting outside enjoying the summer night time ambiance, only to be bombarded with buzzing left, right and centre. It’s no question that bugs are attracted to the lighting we have outside to set the mood, and once they catch sight of it, it becomes irresistible for them to do anything but swarm around it like their life depends on it.

But why is this? What’s the science behind the popular saying “like a moth to a flame”? There seems to be a few different theories as to why bugs are attracted to lighting (almost as much as the Flux team is).

The 2024 answer: insects are not navigating by the light

For decades the standard explanations were about navigation. In February 2024 a study in Nature Communications — “Why flying insects gather at artificial light”, led by researchers at Imperial College London — tested those explanations directly and found something else entirely.

Using stereo-videography in the field in Costa Rica and high-speed motion capture in the laboratory, the team reconstructed insect flight paths around artificial light in three dimensions. What they recorded was not insects steering toward the light. It was insects turning their backs to it.

Flying insects rely on a reflex called the dorsal light response: they hold their back toward the brightest part of their visual field, which under an open sky is up. It is a simple and normally reliable way to stay the right way up in flight. Near an artificial light that same reflex works against them. The insect tilts its back toward the bulb, and because the bulb is close, the angle keeps shifting as the insect moves — producing the orbiting, stalling and inverted flight we read as attraction. The insect is not chasing the light. It is trying to stay level, using a cue that has stopped being trustworthy.

What the earlier theories got wrong

Two explanations dominated before 2024, and both are still widely repeated.

The first was navigation by phototaxis: that insects historically held a constant angle to the moon, and that a nearby bulb corrupts that angle and spirals them inward. The second was the “clear pathway” theory: that an unobstructed light signals open air ahead, so insects fly straight at it. Both are intuitive. Neither survives direct motion capture — the 2024 flight paths show insects doing neither.

So, what can you do to stop being bombarded by uninvited insects this summer?

Wavelength still matters, even though it is not the reason insects gather. Insects see far more strongly into the ultraviolet and blue end of the spectrum than into amber and red, so a lamp that emits little short-wavelength light simply registers less brightly to them — which is exactly what the trap data shows.

A summer-long study was done by Mike and Teresa Justice, two behavioural ecologists with PhDs from the University of North Carolina, Greensboro. The two set up bug traps each night, with a single bulb inside. From night to night, the type of bulb was switched. The results show that incandescent bulbs attract the most insects, while yellow-orange LEDs attract the least. In the mornings, the bulbs were switched off and the trap examined to see how many bugs were caught. Incandescent bulbs had the highest capture rate, followed by CFL, halogen, LED with a cool colour temperature, and a standard ‘bug’ light. At the bottom with the lowest capture rate were warm-coloured LEDs.

So if you’re looking to light up your outdoors this summer, opt for warm yellow-orange LED bulbs to light up your space.

Motion-blurred trails of insects swarming around a streetlight against a black night sky.

Building exterior lighting at OCH Carlington Community, Ottawa

Common questions

What colour of outdoor light attracts the fewest insects?

Warm yellow-orange light. Insects see far more strongly into the ultraviolet and blue end of the spectrum than into amber and red, so a lamp that emits little short-wavelength light simply registers less brightly to them. That is what the trap data shows, and it is the one change that reliably helps.

Do yellow bug lights actually work?

They work, and not because of anything special in the glass. What matters is the spectrum coming out of it. Less blue and ultraviolet, fewer insects. A warm LED does the same job without the tint, and it’s easier to live with on a patio.

Are insects navigating by the moon, then getting confused?

That was the standard explanation for decades, and the 2024 research doesn’t support it. High-speed motion capture of insect flight around artificial light showed something different: they keep their backs turned toward the brightest light, which is a sensible rule under an open sky and a trap under a porch light.

How do bugs get inside light fixtures?

Through the gaps, and then they can’t find their way back out. Most fixtures aren’t sealed: there’s a seam between the trim and the ceiling, a vent in the housing, a lens that clips rather than gaskets. Warmth pulls them further in. If it’s a recurring nuisance outdoors or in a covered entry, ask for a fixture rated for damp or wet locations — the gasket that keeps water out keeps insects out too.

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