Flies can be a major nuisance, invading homes and spreading bacteria and disease. Many people have observed that flies seem to avoid blue light – could this be an effective way to repel flies? In this article, we’ll examine the evidence on whether flies dislike blue light and if blue light traps or repellents could be an environmentally-friendly way to control fly populations.
Do Flies Have a Natural Aversion to Blue Light?
Some research suggests that flies may inherently avoid blue light wavelengths. Flies have specialized photoreceptor cells in their eyes that allow them to see ultraviolet and blue light that is invisible to humans. Scientists theorize that flies may have evolved to instinctively avoid blue light because it mimics the light spectrum of open skies, making flies feel exposed and vulnerable to predators like birds that could spot them against a blue backdrop.
Studies testing how flies react to different wavelengths of light have found that flies show avoidance behaviors when exposed to blue light between 400-500 nm wavelengths. One study published in the Journal of Insect Physiology examined the light avoidance reactions of the common housefly and found that blue light induced the strongest escape responses like flying away or landing compared to white, yellow, red or green lights. The researchers concluded that blue light seems to trigger an innate avoidance reaction in flies.
Another study from the University of Florida tested the effects of different colored lights on house fly movement. They found flies showed the highest levels of avoidance under blue LED lights, with 77% fewer flies entering the blue light zone compared to incandescent yellow light. This provides additional evidence that flies innately avoid blue light wavelengths.
Blue Light May Disrupt Fly Vision
Why do flies seem to inherently dislike blue light? One hypothesis is that certain intensities or wavelengths of blue light may interfere with a fly’s vision and ability to perceive objects and motion.
Flies have eyes specially adapted for detecting motion and faint movements of potential prey. Their vision is tuned to greens and yellows of foliage and grass. Intense blue light with short wavelengths may overstimulate the fly’s blue light photoreceptors, creating a blinding or disorienting effect that causes flies to flee the source of blue light. So blue light may make it physically uncomfortable or difficult for flies to see, overriding their instinct to seek food and shelter.
Blue Skies Signal Exposure
Another theory for fly aversion to blue light has to do with behavior and evolution. Open blue skies may represent a danger zone to flies where they are easily within sights of predators like birds and other insects. Since flies evolved in outdoor environments, they may have an inborn tendency to seek cover and avoid blue light mimicking open sky where they are most visible. Blue light traps may tap into this innate avoidance of open exposed spaces.
Do Blue LED Lights Repel Flies?
Based on the evidence that flies seem to inherently dislike blue wavelengths, some pest control and outdoor lighting companies have developed LED lights that flash blue patterns or beams claiming to repel flies. But do these blue light traps and repellents actually work to reduce fly populations?
Some controlled studies suggest blue LED lights may be somewhat effective at manipulating fly behavior and movements:
– A New Zealand study tested blue LED light strips in a bovine mastitis prevention trial in dairy barns. Blue lighting reduced overall fly counts in the barns by 22% on average compared to white LED light.
– Researchers from AACL Bioflux tested blue LED light effects on the movement of the common housefly. They found 70% fewer houseflies settled in the zone lit by blue LEDs compared to yellow LEDs.
– A study published in the Journal of Medical Entomology examined blue and white LED lights in controlling phorid flies, a common fly pest attracted to warehouses and homes. They found around 20-50% less phorid flies settled under the blue lights.
So field and laboratory trials indicate some measurable repellent effects of blue LEDs for common flies like the housefly. The blue light seems to modify fly behavior enough to deter flies from entering lit areas or force them to settle elsewhere.
Flashing Blue Light May Enhance Effects
Some research indicates that pulsating or flashing blue lights may be even more effective than constant blue light alone. Flashing light disturbs the fly’s vision and makes it harder for them to land or focus on food sources.
One study tested fly repellency of flashing versus continuous blue light. Flashing blue light reduced flies settling on surfaces by over 50% compared to constant blue light. The disorienting pulses of light make flies too uncomfortable to remain in the flashing blue light for long.
Outdoor field tests have found that flashing blue LED strips can decrease outdoor fly populations gathering in a treated area by up to 70% compared to untreated areas. The pulsating light beams seem to overstimulate the fly’s blue photoreceptors, essentially blinding and confusing them so they avoid lit zones.
Positioning of Blue Lights Matters
For optimal results, blue LED repellent lights should be carefully positioned where flies are likely to enter structures, settle, or gather. Placing blue lights pointed at entryways, over countertops, or above gathering areas like patios or outdoor dining spaces creates a “wall” of light that makes these zones uncomfortable for flies. Maintaining blue LEDs in areas where flies congregate is key for maintaining reductions in local fly activity and populations over time.
Are There Any Risks or Downsides to Blue LED Lights?
Some concerns have been raised over excessive exposure to blue wavelengths from LEDs:
– Risk of eye damage – Very intense blue LEDs used in concentrated beams may potentially cause temporary eye pain or damage if gazing directly for extended periods. But most consumer blue light traps and repellents are low intensity and considered eye safe.
– Light pollution – Blue LEDs used outdoors contribute to excessive artificial light pollution that can disrupt ecosystems and natural light-dark rhythms of wildlife. Wise positioning and limiting duration of blue light exposure can help mitigate impacts.
– Human health – There are some concerns that excessive blue light exposure at night from screens or devices may disrupt healthy circadian rhythms. But occasional blue light exposures from insect repellents are not equivalent to prolonged computer screen use.
Most studies indicate occasional blue light exposure from insect traps or repellents pose minimal risk and the benefits likely outweigh potential downsides. But judicious use is still advisable.
Are There Any Non-Chemical Alternatives Besides Blue Light?
For consumers looking for non-chemical fly deterrent alternatives, there are a few other options in addition to blue LED light traps:
– UV Blacklights – Ultraviolet blacklights also attract and electrocute flies without any zappers. The UV wavelengths lure flies in but the lack of visible light makes it harder for flies to escape.
– Fans – High velocity fans can blow flies away from an area. Fans on patios or porches can make it hard for flies to land and settle.
– Fly paper – Non-toxic sticky fly paper can trap flies without chemicals. Positioning fly paper in strategic spots where flies gather or land can capture populations.
– Essential oils – Some natural essential oils like eucalyptus, lemon, and peppermint may repel flies when used in diffusers or sprays. However, effects are limited and require heavy applications.
– Fly zappers – Electric fly zappers attract and electrocute flies without pesticides. However, they kill many beneficial insects too.
Overall, blue LED lighting seems to currently provide the most effective non-chemical fly control solution, leveraging flies’ apparent innate aversion to blue wavelengths. Used properly, blue light traps can provide a significant first line of defense in reducing fly nuisance and health hazards.
Conclusion
Based on controlled studies observing fly reactions to light and field tests of commercial blue LED systems, evidence indicates flies do seem to exhibit an inherent avoidance of blue light wavelengths in the 400-500 nm range. While not a standalone solution, blue light technologies appear able to repel and manipulate fly movements enough to decrease local fly activity by roughly 50-70% when properly positioned in fly gathering zones.
Flashing blue lights may enhance repellency effects by overstimulating fly vision and making it hard for them to land near light sources. Risks of blue LEDs seem minimal if exposure is not excessive. For consumers wanting powerful yet eco-friendly fly control, blue light traps and repellents can be a worthwhile non-chemical deterrent option as part of an integrated pest management program. Going forward, real-world testing will continue to refine optimal blue light uses for sustainable fly management.