Insects are integral parts of the ecosystem. There are millions of insect species that provide benefits to the environment and humans in many ways – as pollinators, pest controllers, recyclers, decomposers etc. On the other hand, some insects can be damaging when they become agricultural pests.
Insects and light
Insects are known to be attracted to different colours of light. Their vision and light sensitivity are different from humans. Understanding insect vision and light preferences can help design lighting systems that are beneficial or detrimental to insects depending on the purpose.
How do insects see light?
Insects have compound eyes made up of multiple light-sensitive units called ommatidia. Each ommatidium acts as an individual visual receptor. The number of ommatidia varies between insect species – bees have around 5,000 while dragonflies have up to 30,000.
The ommatidia are optimised to detect movement and distinguish between dark and light areas. Unlike humans, most insects see ultraviolet (UV) light along with the visible light spectrum. They are generally more sensitive to UV, blue, and green light compared to red light.
Factors determining insect attraction to light
Several factors determine if and how strongly insects are attracted to different colours of light:
- Wavelength of light – shorter wavelengths like UV and blue attract more insects
- Intensity/brightness of light
- Flicker rate – flickering light attracts more insects
- Time of day – insects are more active and attracted to light at night
- Season – light attraction varies through insect life cycles
- Insect species – attraction varies between flies, moths, beetles etc.
Which colour light attracts the most insects?
Research over the past decades has compared insect attraction across the light spectrum from UV to infrared. Overall, UV and short wavelength visible light attract significantly more insects compared to long wavelengths.
A comparative study tested light attraction of different insect orders using UV (350-400 nm wavelength), blue (420-490 nm), yellow (530-590 nm) and red (610-690 nm) lights. The results are summarised in the table below:
| Insect Order | Most Attractive Light Colour |
|---|---|
| Lepidoptera (moths, butterflies) | UV |
| Diptera (flies, mosquitoes) | Blue, UV |
| Coleoptera (beetles) | UV, Blue |
| Hymenoptera (bees, wasps, ants) | Blue, UV |
| Hemiptera (cicadas, aphids, hoppers) | Blue |
Another study tested different wavelength bands and found UV wavelengths from 330 to 380 nm attracted the most moths. Shorter peak UV wavelengths around 350 nm were more attractive than longer wavelengths near 400 nm.
For most major insect groups studied, UV and violet-blue light around 350-450 nm attracts significantly more insects compared to longer wavelength yellow, orange and red light.
Why are insects attracted to UV and blue light?
There are two key reasons why insects are more attracted to ultraviolet and blue light:
- Higher sensitivity – insect eyes have specialized UV and blue light receptors
- Resembles natural cues – Many flowers reflect UV patterns to attract pollinators
Insect compound eyes have specialized photoreceptor cells called UV and blue receptors that are sensitive to shorter wavelengths of light. UV patterns on flowers provide cues to help pollinating insects like bees find nectar. Some night-active insects may navigate using the UV patterns in moonlight.
Artificial night lighting rich in short wavelengths can confuse these insect behaviors and attract more insects to the light sources.
How to reduce insect attraction to outdoor lighting?
The key strategy to reduce light attraction for insects is using longer wavelength lighting deficient in UV and blue light. Some guidelines include:
- Use LED/bulb lights with minimize emission below 500 nm
- Use lights with red/orange filters or coatings
- Avoid fluorescent lights which have high UV/blue emission
- Use lower intensity lights directed only to where needed
- Turn off lights when not required
Longer wavelength yellow, amber and red light attracts significantly fewer insects. Red light allows human vision outdoors at night while minimizing ecological impacts on insects. Motion-activated lighting and directing light only where needed also help reduce light pollution.
How can targeted insect attraction be achieved?
UV and blue-rich light can be leveraged to attract beneficial insects like pollinators or trap unwanted pests for monitoring or control. Some examples include:
- UV reflectors to increase bee visits to crops
- Blue/UV LED lights in bee traps for hive inspections
- Light traps for mosquito surveillance and control
- Short wavelength light to attract and trap agricultural pests
Conversely, yellow, amber and red light can be used for outdoor lighting where minimal insect attraction is desired. Recent advances in LED lighting technology have enabled tunable, customizable lighting spectra for specialized applications targeting or avoiding insect attraction.
Conclusions
Insects are most attracted to ultraviolet and blue light in the 350-500 nm wavelength range, and less attracted to longer wavelength yellow, amber and red light.
This is due to ultraviolet and blue light receptors in insect eyes and resemblance to natural cues that insects evolved to follow. Targeted use of short or long wavelength lighting can respectively attract beneficial insects or reduce attraction of damaging pests to outdoor lights.
Advances in tunable LED lighting open up flexibility in designing insect-friendly outdoor lighting minimizing ecological disruption while retaining visibility and utility.
