Gnats target your eyes because the tears and moisture around them are a rich source of proteins, salts, and lipids that certain fly species have evolved to feed on. Some gnats land on any exposed mucous membrane they can find, but your eyes are a particular draw because lachrymal secretions provide nutrients these tiny insects cannot easily get elsewhere. The phenomenon is so well-documented that entomologists have a name for the worst offenders: eye gnats. Understanding what attracts them and why they are so persistent is the first step toward keeping them off your face.
What Makes Your Tears Worth Chasing
Tears are not just salty water. They contain a mix of proteins, lipids, and dissolved minerals that serve as a genuine food source for small flies. The thin film of moisture on the surface of your eyes and the surrounding skin offers something that sweat alone does not: a concentrated cocktail of organic compounds in a small, accessible area. For a gnat weighing a fraction of a gram, a single visit to the corner of your eye can deliver meaningful nutrition.
This feeding behavior is called lachryphagous feeding, and it shows up across multiple insect families worldwide. Male flies of certain species are especially drawn to lachrymal secretions, partly because these secretions provide proteins that males may not get from other food sources like nectar or decaying fruit. The behavior is not random or accidental. These insects have evolved sensory systems tuned to detect the chemical signatures coming from the eye region of mammals and birds.
Which Insects Are the Worst Offenders
When people complain about gnats in their eyes, they are usually dealing with one of a few groups. The most notorious in the United States are the true eye gnats in the genus Liohippelates, tiny flies in the family Chloropidae. Two species in particular, Liohippelates pusio and Liohippelates collusor, have been the subject of research and pest control efforts since the 1930s and are widespread across the southern and southeastern United States.1Journal of Integrated Pest Management. Eye Gnat (Liohippelates, Diptera: Chloropidae) Biology, Ecology, and Management: Past, Present, and future Another common species in the Southeast is L. bishoppi.2EDIS. Eye Gnats, Grass Flies, Eye Flies, Fruit Flies Liohippelates spp. (Insecta: Diptera: Chloropidae) These flies are tiny, often just one to two millimeters long, which makes them almost impossible to see until they are already on your face.
But Liohippelates are not the only culprits. In Europe, flies in the genus Phortica (family Drosophilidae) are known to seek out lachrymal secretions from animals and humans. Male Phortica variegata are specifically attracted to eye secretions, a behavior that sets them apart from most of their fruit-fly relatives.3PubMed. Phortica variegata as an intermediate host of Thelazia callipaeda under natural conditions: evidence for pathogen transmission by a male arthropod vector And in tropical regions, various other small flies have been documented engaging in tear-feeding on livestock and wildlife. The common thread is that wherever there are eyes producing tears, some local fly species has figured out how to exploit them.
How Gnats Track You Down
Getting from wherever they are resting to the surface of your eyeball requires gnats to detect you from a distance and then home in. The process works in stages, and research on biting and non-biting flies suggests a general pattern shared across many small flying insects.
The first signal is usually carbon dioxide. When you exhale, you release a plume of CO2 that spreads downwind and can be detected by insects from several meters away. Research on mosquitoes has shown that exposure to a CO2 plume more than doubles the number of insects that take flight and begin actively searching for a host. Critically, CO2 does not just get them moving; it switches on their visual tracking system. In experiments, mosquitoes exposed to CO2 became strongly attracted to visual objects in the orange and red wavelengths that dominate human skin color, while those in clean air showed no such preference.4PubMed Central. The olfactory gating of visual preferences to human skin and visible spectra in mosquitoes Although this particular study examined mosquitoes rather than gnats, the principle of odor-activated visual tracking appears to be widespread among host-seeking flies.
Once in your vicinity, gnats pick up on shorter-range chemical cues. Body heat, skin odor compounds like lactic acid, and the specific volatile chemicals emanating from your eye area all help guide them to their target. The moisture gradient around your eyes and nose provides a final beacon. Eye gnats are so persistent partly because these short-range cues are strong and constant: as long as your eyes are producing tears, the signal does not fade.
Why They Are So Hard to Swat
If you have ever tried to wave a gnat away from your face only to have it return within seconds, you are not imagining its persistence. Small flies are remarkably agile fliers, and their aerodynamics make them difficult to dislodge permanently.
Research on insect flight mechanics has shown that flies with asymmetric wing beats, where the upstroke and downstroke cover different angles, are partly passively stable in wind. This means they can maintain controlled flight even when hit by gusts or turbulence, including the breeze you create by waving your hand.5PubMed Central. Flying Into the Wind: Insects and Bio-Inspired Micro-Air-Vehicles With a Wing-Stroke Dihedral Steer Passively Into Wind-Gusts When a sideways gust hits these insects, their wing-beat geometry automatically rotates them to face into the wind rather than being blown off course. The result is that your frantic hand-waving may push a gnat a short distance, but it recovers its orientation almost instantly and flies right back.
Their size works in their favor too. At one to two millimeters, eye gnats operate in a regime where air feels much thicker relative to their body than it does for us. They can change direction rapidly, hover with minimal energy expenditure, and slip through the gaps between your fingers. Combine that with their strong motivation to reach your eye secretions, and you get an insect that simply does not give up after one unsuccessful attempt.
Can Gnats Around Your Eyes Actually Make You Sick
The annoyance factor alone would be enough reason to keep gnats away, but some species carry genuine health risks. Eye gnats have long been associated with outbreaks of bacterial conjunctivitis, commonly known as pink eye. When Liohippelates species feed on the moisture around one person’s eyes and then move to another person, they can physically transfer bacteria from one host to the next. This was documented repeatedly in the southern United States in the mid-twentieth century and was one of the main motivations for early eye gnat control programs.1Journal of Integrated Pest Management. Eye Gnat (Liohippelates, Diptera: Chloropidae) Biology, Ecology, and Management: Past, Present, and future
A more unusual risk involves parasitic eyeworms. In Europe and parts of Asia, the nematode Thelazia callipaeda is transmitted by Phortica flies that feed on lachrymal secretions. Male Phortica variegata act as intermediate hosts for the parasite under natural conditions; when an infected fly visits the eye of a dog, cat, or occasionally a human, it can deposit larval worms that mature in the conjunctival sac.3PubMed. Phortica variegata as an intermediate host of Thelazia callipaeda under natural conditions: evidence for pathogen transmission by a male arthropod vector Cases of Thelazia infection in dogs have been identified in the United Kingdom, and the fact that the Phortica vector is already present there raises concerns about the parasite establishing itself in new regions.6PubMed Central. Three cases of imported eyeworm infection in dogs: a new threat for the United Kingdom Human cases are rarer but have been reported in Italy, France, and other parts of southern Europe. The infection causes irritation, excessive tearing, and in severe cases, damage to the cornea.
For most people in most places, gnats around the eyes are a nuisance rather than a medical emergency. But if you live in or travel to areas where Thelazia or bacterial eye infections are known to circulate, the stakes of keeping gnats off your face go up.
Practical Ways to Keep Gnats Away from Your Eyes
There is no single magic solution, but a combination of strategies can make a real difference.
- Sunglasses: A physical barrier is the most reliable defense. Wrap-around styles that sit close to the face leave fewer gaps for tiny gnats to slip through. This is especially useful during outdoor exercise when you are producing more CO2 and body heat, both of which attract insects.
- Hats with brims: A wide brim creates a shaded zone around your face. Since many eye gnats are most active in sunny conditions and orient toward contrast between light and dark areas, reducing the visual contrast around your eyes can help.
- Fans and air movement: Eye gnats fly slowly. Even a small handheld fan or a table fan on an outdoor patio creates enough airflow to keep them at a distance. This is often the simplest solution for stationary situations like eating outdoors.
- Light-colored clothing: Research on host-seeking flies consistently shows stronger attraction to darker colors and wavelengths associated with skin tones. Wearing lighter clothing will not make you invisible to gnats, but it reduces one of the visual cues they use to find you.
- Avoid peak times and places: Eye gnats tend to be most active during the warmest hours of the day, especially in open, sunny areas with loose or sandy soil where they breed. If you know you are in eye gnat territory, scheduling outdoor activities for early morning or late afternoon can reduce encounters.
Repellents That Work
DEET-based repellents remain the standard recommendation for most biting and nuisance flies, but they are not always ideal for applying near your eyes. Spraying DEET on the skin around your eye area can cause stinging and irritation, which somewhat defeats the purpose. A better approach is to apply repellent to a hat brim or bandana rather than directly to facial skin.
For people who prefer plant-based options, para-menthane-3,8-diol (PMD), derived from lemon eucalyptus oil, has shown strong performance against various flies. In laboratory testing, a 20% PMD solution provided complete protection for over 300 minutes, compared to just 22 minutes for the unrefined essential oil alone.7Comptes Rendus. Chimie. Green synthesis of para-Menthane-3,8-diol from Eucalyptus citriodora: Application for repellent products The difference matters: raw eucalyptus oil wears off quickly, while the refined PMD compound lasts for hours. Look for products listing PMD or “oil of lemon eucalyptus (refined)” on the label rather than raw essential oil blends, which tend to evaporate and lose effectiveness fast.
What Does Not Work Well
Citronella candles and bracelets impregnated with plant oils are popular but generally ineffective against eye gnats. The active compounds disperse too quickly in open air to maintain a protective zone around your face. Bug zappers are similarly unhelpful: they attract insects with UV light, and eye gnats are not strongly drawn to UV. You may end up killing moths and beetles while the gnats continue undeterred.
Swatting, as discussed earlier, provides only momentary relief. The gnat’s flight stability and strong motivation mean it will be back in seconds. Your energy is better spent on barriers and repellents than on hand-waving.
Why Some People Seem to Attract More Gnats Than Others
You are not imagining it if gnats seem to prefer you over the person standing next to you. Individual variation in body chemistry plays a role. People who produce more CO2 (larger individuals, those who are exercising, pregnant women) send out a stronger long-range signal. Differences in skin microbiome composition also affect the specific volatile compounds your skin emits, and some profiles are more attractive to flies than others.
Sweat matters too, but not all sweat equally. The eccrine sweat glands concentrated on your forehead and around your eyes produce a thin, watery secretion that is especially attractive to eye gnats because it closely mimics lachrymal fluid in salt and protein content. People who sweat heavily from the face during exercise or in hot weather may find themselves particularly besieged.
There is also a visual component. Research on mosquitoes found that CO2 exposure triggered attraction specifically to the orange and red wavelengths characteristic of human skin, while cooler colors like blue and green were not attractive.4PubMed Central. The olfactory gating of visual preferences to human skin and visible spectra in mosquitoes If this preference extends to gnats, as many entomologists suspect, then factors like skin tone, clothing color, and even the contrast between your skin and your hat could influence how attractive you appear from a gnat’s perspective.
Tear-Feeding Beyond Gnats
The strategy of feeding on eye secretions is not limited to tiny flies. It turns out that tear-feeding, or lachryphagous behavior, has evolved independently in several insect lineages, suggesting it offers a real nutritional payoff worth the risk of approaching a much larger animal’s face.
In Madagascar, researchers discovered a moth species, Hemiceratoides hieroglyphica, that feeds on the tears of sleeping birds. The moth belongs to a lineage that includes both fruit-feeding and blood-feeding species, but it has evolved a uniquely specialized proboscis tipped with hooks, barbs, and spines that allow it to pry under a sleeping bird’s closed eyelid and access the tears beneath.8PubMed Central. Malagasy birds as hosts for eye-frequenting moths The armature on this proboscis is structurally similar to that of piercing moths that feed on fruit or blood but distinctly different from other known tear-feeding moths, indicating that the adaptation arose from a piercing ancestor rather than a lapping one.
In Southeast Asia and parts of South America, other moth species have been documented landing on the faces of large mammals, including cattle, deer, and occasionally sleeping humans, to drink tears. Some bee species in Thailand are known to visit the eyes of people and animals for the same purpose. The common thread across all these cases is that tears offer a rare combination of accessible protein and salts that these insects struggle to find in other food sources, especially in environments where flowers or animal dung (the usual alternatives for getting sodium and amino acids) are scarce.
The existence of so many independent lineages of tear-feeders across the insect world puts the humble eye gnat in context. When a gnat zeros in on your eye during a summer walk, it is following a survival strategy that has been reinvented by evolution over and over again, in species as different from each other as tiny chloropid flies and large noctuid moths. Your tears, it turns out, are one of nature’s more sought-after beverages.