Flies seem to have an uncanny ability to zero in on people’s eyes, buzzing around faces and going for the eyes specifically. This irritating and potentially dangerous behavior has long perplexed people. Here we will explore some of the main theories as to why flies exhibit this eye-seeking behavior.
Flies are attracted to moisture
One of the most commonly cited reasons flies go for the eyes is that eyes contain moisture. Fly eyes themselves are moist and covered with a film of liquid to keep them from drying out. They are naturally attracted to moisture. Tears and mucus around human eyes presents an external source of moisture that attracts flies. The wet surface of the eyeball itself may also draw flies in.
Eyes reflect light
In addition to containing moisture, eyes are reflective. The dome-like shape of the eyeball causes it to reflect light. This presents a reflective surface and bright spot that attracts flies visually. The effect is similar to how certain flies are attracted to shiny surfaces, only the eye’s wet, convex shape makes it especially eye-catching. The constant tiny movements of the eyeball may also enhance the flickering reflective effect that calls out to flies.
Eyes produce smells that attract flies
Research suggests flies may also be attracted to the smell produced by eyes and tears. Tears contain proteins and other compounds that produce scents. There is evidence that flies’ olfactory receptors detect these eye-related scents and navigate toward them. The smell provides a signal that indicates the presence of moisture, making flies more likely to zero in on the eyes.
Flies mistake eyes for flowers and other objects
Some researchers propose that flies do not purposefully target eyes but mistakenly approach them. From a distance, the colorful circle of the iris ringed by white sclera may resemble a flower or other object that flies navigate toward. The eye’s complex pattern and coloration may mimic things like petals and bullseyes that are attractive landing spots for flies. So the eyes become unintended landing pads when flies make visual mistakes.
Eyes dont swat flies away
Another simple theory is that flies preferentially go for people’s eyes because the eyes don’t swat flies away like hands and other body parts will. Being constantly shooed away from the rest of the body could drive flies to the less bothersome eyes by process of elimination. Less motion from eyes means flies aren’t deterred from landing there once they get close to a person’s face.
Eyes emit CO2
Like the mouth and nose, eyes give off carbon dioxide as people exhale. Flies detect CO2 and will land on eyes along with these other facial orifices since they emit steady streams of this gas. The moist membranes around the eye also release extra CO2 and heat that may slightly amplify this effect.
Eyes are unable to blink while looking directly at flies
An interesting factor is that people tend to stare directly at flies once they notice them buzzing around their heads. This reaction keeps the eyes open and unable to blink while looking at the fly. With normal blinking impeded, flies have more opportunity to dart in and make contact with the unprotected eyeball surface. This may at least partially contribute to flies’ tendency to land on and get close to eyes.
Flies see certain wavelengths of light better
| Wavelength | What flies see best |
|---|---|
| 300-400 nm | UV light |
| 400-475 nm | Violet-blue light |
Research shows flies are especially sensitive to certain wavelengths of light, particularly in the ultraviolet (UV) and violet-blue end of the spectrum. The eyes happen to strongly reflect UV light. This makes them stand out as bright spots for flies able to see these wavelengths. So the eyes may be visually conspicuous targets compared to less UV-reflective skin and other body parts.
Conclusions
In summary, there are a variety of factors that draw flies to human eyes or make eyes opportune landing spots:
– Moisture on the eyes attracts flies looking for water sources
– Reflective qualities of eyes attract some flies visually
– Smells produced by eyes and tears contain compounds flies can sense
– Some flies may mistake eyes for other objects
– Eyes don’t deter flies by swatting them away like hands would
– CO2 emitted from eyes helps flies hone in
– People tend to stare at flies, keeping eyes open and vulnerable
– UV light reflected by eyes makes them more visible to flies
The exact interplay of these different elements that drives flies to eyes is still being studied. But most experts agree flies do not purposely intend to annoy humans by targeting eyes. Their behavior stems from innate survival programming to seek food, moisture and breeding sites. The human eye happens to provide attractive cues that exploit these natural fly impulses in undesirable ways. Understanding this can hopefully lead to better ways to outsmart flies and prevent them from causing eye irritation and health risks.