Flies are a common nuisance that we have all dealt with at some point. Their persistence and ability to quickly multiply make them difficult to control. Understanding what attracts flies to humans can help us take steps to prevent infestations and minimize contact with these disease-carrying insects.
Some key questions we will answer include:
– What scents and smells attract flies?
– What visual cues draw flies to humans?
– How do flies locate and zero in on targets?
– What factors lead to increased fly activity around people?
By identifying the main reasons flies are attracted to humans, we can disrupt these signals and create an environment less appealing to flies. Read on to learn more about the science behind what lures flies to humans.
Scents That Attract Flies
Flies have an incredibly strong sense of smell and can detect odors over long distances. Certain scents seem irresistible to flies, drawing them to potential food sources or breeding sites. Here are some of the scents that strongly attract flies:
Human Sweat and Body Odor
Flies use smell to locate warm-blooded animals to feed on. Human sweat and skin secretions contain ammonia and fatty acids that smell like food to flies. Our natural body odors provide flies with the scent trail they follow to find hosts to bite and extract blood from.
Food Residue and Grease
Flies have receptor cells that respond to amines found in rotting, fermenting food scraps. Anything from meat juices to crumbs to leftovers can provide an attractive odor. Greasy residues also contain fatty acids that appeal to flies. Garbage cans and compost bins give off scents that signal ideal breeding and feeding sites.
Animal Feces and Manure
Animal droppings contain ammonia similar to human sweat and skin secretions. The smell attracts flies seeking protein sources. Flies lay eggs on fresh manure, providing nourishment for the emerging larvae. Barnyards, stables, and pet waste can draw swarms of flies with their pungent odor.
Open Wounds
Some flies target open sores or ulcers to lap up blood and tissue discharges. The smell of accessible blood and pus in a wound acts like a magnet. Hospital patients and animals with untreated wounds are at risk of attracting flies.
Visual Cues That Attract Flies
Beyond smell, flies also use visual cues to identify promising locations to obtain a blood meal or breeding site. These are some of the visual stimuli that catch a fly’s attention:
Dark Colored Clothing
Flies are particularly drawn to dark colors like black, dark blue, and red. Dark clothes against a light background help flies spot potential hosts from a distance. Dark colors also retain more heat than light colors, making flies think a dark shirt or pants could be a warm-blooded animal.
Skin Tone
Some flies preferentially target people based on skin tone. Mosquitoes, for example, are more attracted to darker skin tones. The higher melanin content makes blood vessels closer to the skin surface easier for mosquitoes to see and target.
Motion
Movement catches a fly’s eye and makes them zoom in to investigate. Swatting at flies or fanning yourself when hot provides motion stimuli that draw more flies to you. Rocking in a chair or pacing triggers a fly’s motion detection, bringing them buzzing around.
Reflected Light
Flies orient towards linearly polarized light. Reflective surfaces like glass windows, cars, water, and shiny jewelry polarize light in a way that attracts flies. Their eyes detect the change in polarization compared to the background and they swarm to check it out.
Contrast
Flies easily distinguish contrast and are pulled towards high contrast boundaries. Light skin against a dark shirt provides the type of contrast that helps flies orient from a distance. High contrast also signals potential resources to flies, making items that stand out from the background more attractive.
How Flies Locate Their Targets
Flies combine smell and vision cues to pinpoint promising sources of food, breeding sites, and hosts. Here is a look at some of the key ways flies home in on specific targets:
Odor Plumes
Flies moving upwind detect bands of odor called plumes. They orient themselves towards the most concentrated band of scent and then follow it to the source like dogs tracking a scent. If the odor remains steady, the fly identifies its target.
Heat Detection
Flies can sense infrared radiation, allowing them to seek out warm-blooded hosts like humans and animals. Cooler areas on the body surface also attract flies looking for veins and capillaries under thinner skin.
Carbon Dioxide
Flies detect carbon dioxide gas emitted in breath. From up to 50 feet away, flies can sense CO2 plumes and fly up the increasing concentration gradient to reach the exhaling host.
Optical Cues
Once in visual range, flies rely on optical cues like shape, size, speed, contrast and polarization of light to steer towards targets. Flies excel at judging distance and positioning themselves to land on hosts.
Proboscis Extension
When flies get within 4 inches of a potential food source, they extend their sponging mouthpart called the proboscis in anticipation of drinking and tasting. This reflex primes them for rapid feeding if the source proves suitable.
Factors That Increase Fly Activity Around Humans
Flies need access in order to become pesky around human environments. Certain conditions favor increases in fly populations and contact with people:
Access to Food Waste
Improperly sealed food and compost waste provide breeding sites for flies. Maggots feast on scraps, emerging as adult flies in 4-7 days. Easy meals let flies multiply exponentially.
Access to Buildings
Open doors and windows, gaps under doors, and holes in screens allow flies entry to human dwellings. Once inside, they congregate wherever people are. Sealing entry points prevents indoor infestations.
Livestock and Pets Nearby
Animal facilities generate odor plumes full of attractants like manure, waste, sweets in feed, moisture, and decaying material. Farms, stables, and kennels provide flies with ideal breeding conditions.
Changing Seasons
Fly populations peak in summer and fall when temperatures are warm. The heat speeds up their life cycle. Cooler temperatures in spring and autumn also drive flies to seek warm indoor spaces.
Poor Sanitation
Unclean environments allow food residue, standing water, litter, and waste to accumulate. These are perfect conditions for flies to reproduce and lead to greater harassment of humans.
Conclusion
Flies detect strong odor cues like body odors, food waste, and manure that signal ideal feeding, breeding, and blood meal sources. Visually, flies orient towards contrast, motion, and reflected light that could indicate a warm-blooded host. Odor plumes and heat detection then guide them straight to human targets. Reducing access to food waste, sealing entry points, and improving sanitation all help make areas less accommodating to flies. Understanding the science behind what attracts flies empowers us to take proactive steps to prevent infestations and minimize contact with disease-carrying flies.
References
| Author | Year | Title |
| Dethier, V. G. | 1976 | The Hungry Fly: A Physiological Study of the Behavior Associated with Feeding |
| Gibson, G. & Torr, S.J. | 1999 | Visual and olfactory responses of haematophagous Diptera to host stimuli |
| Murdoch, W. W. | 1969 | Switching in General Predators: Experiments on Predator Specificity and Stability of Prey Populations |
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