Flies are known for buzzing around and landing on people seemingly just to be aggravating. But in reality, there are biological reasons that cause flies to behave this way. Understanding fly behavior can help shed light on why they insist on pestering humans.
Flies Are Attracted to Humans for Food
One of the main reasons flies pester humans is that they are attracted to food sources. Flies eat by vomiting digestive juices on their food source and then sucking up the liquefied remains. They have sponging mouthparts that are perfect for lapping up nutrient-rich liquids.
Humans provide plenty of appetizing food sources for flies. For example:
- Sweat contains salts and minerals that flies require in their diet.
- Tears keep flies hydrated.
- Food particles around the mouth or on unwashed hands give flies a convenient meal.
Flies also feed on feces and garbage. Any areas where humans leave behind organic waste attract flies looking for their next meal.
Flies Have a Strong Sense of Smell
Not only are humans a great food source, but flies can detect them from far away. Flies primarily use their sense of smell for finding food. They have antennae covered in smell receptors that can pick up scents from up to 100 feet away.
The smells that attract flies most are:
- Ammonia – found in sweat and urine
- Volatile fatty acids – given off by skin oils and perfumes
- Amines – emitted by decaying meat and fish
When a fly picks up one of these scents associated with food, waste, or humans, it will quickly zero in on the source.
Flies Seek Out Warm Areas
In addition to seeking out food by smell, flies like to gather in warm places to regulate their body temperature. A fly’s small body loses heat rapidly, so it needs warmth to raise its body temperature enough for flight.
Some warm areas that attract flies include:
- Sunny spots indoors near windows
- Heated rooms during colder months
- Places where the sun hits on a building exterior
- Warm bodies of humans and animals
Flies will land on humans to soak up the warmth of their body heat. By resting on someone’s arm or leg, flies can raise their muscles to optimal temperature for taking off and flying again.
Flies Are Social Insects
Flies also tend to gather around humans because they are social insects. If one fly finds a promising location, it will release pheromones that attract other flies.
Soon a large group of flies may accumulate in an area where food, warmth, or other benefits exist. They recognize that gathering together provides advantages such as:
- Increased safety from predators
- Better detection of resources when searching as a group
- Mating opportunities
A human’s presence signals a good habitat to take advantage of. Plus, flies do not like to live alone in isolation.
Flies Have Limited Mobility
Fly behavior also seems annoying to humans simply because flies have limited mobility in flight. A fly’s flight patterns consist of rapid takeoffs and landings, hovering in place, and accidentally crashing into objects.
Reasons flies appear clumsy in flight include:
- Short wings that must beat extremely fast, up to 200 times per second
- Difficulty stabilizing such a lightweight body in the air
- Large heads that throw off their center of gravity
- Large eyes that distort peripheral vision
Flies cannot gain much momentum due to their small size. So they use humans as convenient places to land frequently as they move around in starts and stops.
Flies Groom Themselves on Humans
Flies spend a great deal of time grooming themselves, and humans provide convenient places for them to do this. Like cats, flies lick themselves to clean their bodies. Their legs serve as brushes to remove debris and spread cleansing secretions around.
Landing on humans allows flies to regularly perform their hygiene routine. A fly’s mouth can act like a sort of washcloth to wipe grime off its body. The tiny hairs covering a fly also trap and accumulate dirt and dust that needs constant removal.
Sitting on humans gives flies warm places to settle while they clean themselves off. They can then easily take off again once grooming is complete.
Flies Have Annoying Life Cycles
The reproductive habits of flies also lead them to swarm humans at certain times. During warmer months, the fly life cycle speeds up resulting in large populations built up by summer.
Key facts about the fly life cycle include:
- Female lays up to 500 eggs about every two weeks
- Eggs hatch into larvae within 8-20 hours
- Larvae develop for 3-25 days before pupating
- Adults emerge after 2-14 days as pupae
- New flies reach sexual maturity in 7-10 days
Within just two weeks during prime conditions, two flies can produce hundreds of offspring. This exponential population growth means humans inevitably encounter hordes of flies.
Flies Bite Humans
While female flies seek warm-blooded mammals as hosts to lay their eggs on, male flies have an interest in humans for mating opportunities. Only female flies bite humans, needing blood to develop their eggs. But male flies follow them around in hopes of reproducing.
Some reasons male flies pester humans include:
- Hoping to intercept females looking to bite
- Attempting to mate with females actively drawing blood
- Waiting for females to finish feeding before mating
The male flies do not directly bite humans. But their pursuit of females often places them right next to humans as they manage to successfully mate after feedings.
Flies Seek Moist Areas on Humans
Like many insects, flies require hydration to survive. With small bodies, they face rapid water loss. Flies land on humans because people offer them sources of moisture.
Ways flies get water from humans include:
- Drinking sweat directly from skin
- Consuming tears around eyes
- Feeding on saliva from lips
- Lapping wet mucus membranes
- Regurgitating on moist foods people eat and slurping it up
Without access to humans as a water resource, flies would dry out and die much quicker after emerging from their pupae. The moist surfaces of people’s bodies provide ideal hydration stations.
Flies Try to Steal Human Food
Of course, the most obvious reason flies pester humans is to get access to their food. Flies are always on the lookout for an easy meal.
Flies want to sneak a quick bite of whatever people are eating. This can include:
- Meats
- Fruits
- Vegetables
- Cheese
- Baked Goods
- Candy
- Soda
- Alcohol
Any human food likely contains something flies would find tasty. So they loiter around outdoor barbecues, lunches, and sticky fingers hoping to steal some nutrients. Even at restaurants, flies mine for crumbs under tables or on seats.
Flies Have an Annoying Buzz
The loud droning buzz flies make as they zip around is another thing humans find irritating about them. The primary source of a fly’s buzzing is the vibration of its wings beating rapidly.
Characteristics of the fly wingbeat include:
- Wings beat at 130-190 cycles per second
- A fly zips its wings up and down for flight stabilization
- Special mechanisms keep their flight muscles warm for constant motion
With wings flapping hundreds of times per second, they inevitably create an annoying buzz. The sound also allows flies to communicate with each other while in flight.
Flies Spread Diseases
Not only are flies just a nuisance, they also spread diseases that can cause serious illness. Flies transmit diseases in two main ways:
- By directly transferring disease-causing bacteria, viruses, or parasites onto food that humans then eat
- Through their contaminated vomit and feces full of pathogens
Diseases carried by flies include:
- Salmonella
- E. coli
- Cholera
- Dysentery
- Campylobacter
- Ophthalmia
- Tapeworms
- Pinworms
Flies pick up these pathogens from garbage, feces, or dead animals. A single fly can carry over 500,000 bacteria on its body.
Flies Have Annoying Life Stages
Not only are adult flies bothersome, but their larvae are also disgusting pests. Fly maggots, the worm-like larvae stage, thrive on moist, organic material. Often masses of writhing fly maggots are seen:
- In trash bins and compost piles
- On animal waste and roadkill carcasses
- In latrines and sewers
- Around leaks or moist ceilings and walls
The squirmy, tiny maggots have voracious appetites. Just a small handful can rapidly devour pounds of waste. Seeing thousands of maggots congregating is both nauseating and annoying.
Flies Have No Manners
Ultimately, flies pester people because they have no manners! They exhibit obnoxious behaviors that contradict social norms and etiquette:
- Interrupting conversations or tasks by landing on faces
- Touching food with dirty feet
- Biting ankles or calves leaving itchy welts
- Regurgitating on serving dishes
- Buzzing insistently around ears and heads
- Hovering in front of computer screens or televisions
- Gathering in hordes on walls, food, or countertops
Flies do what they want without regard for humans. Their behaviors understandably frustrate and aggravate people trying to live their daily lives without these annoyances.
Conclusion
Flies pester and bother humans for a variety of biological and behavioral reasons. They need food, water, warmth, shelter, and breeding sites to survive, and human habitats meet these requirements well. Fly anatomy and short lifespans also contribute to their constant presence trying to meet their needs. While flies do nothing malicious on purpose, their actions interfere with human comfort and activities.
Understanding the science behind fly habits can help humans better manage these annoying pests. Sanitation, traps, screens, and other deterrents can reduce problems flies cause. But their amazing persistence and adaptability means humans will likely never be completely fly-free.
In the battle between flies and humans, flies continue buzzing around us thanks to their biological programming. Human awareness, tolerance, and pest management will be needed to find ways of co-existing less obtrusively with these pests that love to annoy us.