Flies have been around for millions of years and have evolved to evade predators and survive in various environments. However, they do have natural enemies that help keep fly populations in check. Knowing what preys on flies can provide insights into managing fly problems through biological pest control methods.
Spiders
One of the most common natural predators of flies are spiders. Most spiders will readily catch and eat flies that become ensnared in their webs. Some species like crab spiders and jumping spiders actively hunt flies as well. Spiders paralyze flies with venom and then wrap them in silk for later consumption. Just one spider web can trap dozens of flies at a time.
Common spider families that prey on flies include:
- Jumping spiders
- Crab spiders
- Orb weaver spiders
- Cellar spiders
- Tangle web spiders
Spiders are so adept at catching flies, that researchers have looked at using artificial spiderwebs to help control flies. Spiderwebs capture flies through their design and adhesive properties. Artificial webs made with similar physical properties can passively trap flies without the need for a living spider on site.
Other Insects
In addition to spiders, many other insects feed on flies as well. These include:
- Praying mantises – These ambush predators readily capture and consume flies.
- Dragonflies – Both the adult and nymph stages prey on flies.
- Antlions – The larvae dig cone-shaped sand traps to capture flies and other small insects.
- Lacewings – The alligator-like larvae have large, hollow mandibles perfect for snatching flies.
- Ladybugs – Adults and larvae will eat fly eggs and larvae.
- Ground beetles – Many species eat fly larvae.
- Parasitoid wasps – The larvae feed on and kill fly pupae.
- Predatory flies – Larger flies prey on smaller ones.
Encouraging these predatory and parasitic insects can help reduce fly populations without the use of pesticides. This is the concept behind biological control programs.
Birds
Birds also consume large numbers of flies and insect pests. Fly-catching bird species that make up a large part of their diet include:
- Swallows
- Swifts
- Nighthawks
- Flycatchers
- Warblers
- Phoebes
- Chickadees
- Sparrows
- Wrens
- Martins
Birds use a variety of techniques to catch flies. Swallows and swifts are masters of aerial maneuvers, plucking flies right out of the air. Flycatchers make short aerial sallies to capture flies. Other birds glean flies off foliage or the ground. Phoebes even catch flies by dropping down on them from perches.
Studies have shown:
- A colony of 500 purple martins can consume 250,000 flying insects per day, including flies.
- Chickadees need about 5000-9000 flies per day to raise a clutch.
- A single barn swallow can catch up to 1000 flies and other insects per day during nesting season.
Attracting insect-eating birds is an eco-friendly way to control flies and avoid pesticides. Placing birdhouses, roost boxes, bird baths, and native plants that provide food and shelter can encourage bird predators to frequent an area and feast on flies.
Bats
Bats are incredibly adept nighttime fly hunters. Using echolocation, bats can detect and capture flying insects, including flies, right out of the air. Just one bat can eat:
- 500-1000 mosquito-sized insects per hour
- 4,000-8,000 flies and other insects each night
Studies of bat scat and stomach contents have found flies make up a substantial part of certain bat species’ diets, including:
- Mexican free-tailed bats
- Big brown bats
- Little brown bats
- Pallid bats
- Townsend’s big-eared bats
Supporting natural bat habitats like caves, forests, and wetlands can allow bat populations to thrive and feast on pest flies. Installing bat houses also encourages bat residency in yards and gardens where flies may be problematic.
Amphibians and Reptiles
Frogs, toads, lizards, and snakes also consume flies. Most amphibians and reptiles are opportunistic feeders and will eat any insects they can capture, including flies. Some examples include:
- Green frogs – Mostly eat insects as adults, including up to 85% flies.
- Garter snakes – Flies make up about 35% of their diet.
- Anoles – Consume various small insects like flies.
- Geckos – Feed on moths, flies, mosquitoes and more.
Providing wetland habitat and hiding places helps these creatures thrive while keeping fly numbers in check. Certain plants may also attract fly-eating amphibians and reptiles. For example, some lizards are drawn to bright flowers that also attract flies.
Fish
For flies near water sources, fish can be important predators. Fish like bluegills, rainbow trout, perch, bass, and catfish will all readily consume flies at the water’s surface. Even bottom-dwelling fish like carp may rise to the surface to grab an easy fly meal.
Dragonfly nymphs are also major aquatic predators of fly larvae. Maintaining proper aquatic habitats and food webs helps support fly-eating fish, dragonflies, and other beneficial species.
Other Vertebrates
In addition to birds, bats, amphibians, reptiles, and fish, other vertebrates prey heavily on flies, including:
- Shrews
- Frogs
- Toads
- Chameleons
- Sugar gliders
Their quick reflexes and appetites allow them to gorge on flies. Certain species like chameleons and frogs even have specialized body parts and tongues for grabbing flies.
Fly Traps
There are also multiple devices designed specifically to trap and kill flies. These include:
- Fly tape – Sticky tape that ensnares flies when they land on it.
- Fly light traps – Attract flies with UV light and capture them on sticky boards.
- Bottle traps – Lure flies in with bait but prevent escape.
- Fly zappers – Electric grids that kill flies on contact.
When used properly indoors or outdoors, fly traps can capture thousands of flies. They are a chemical-free way to suppress fly populations.
Natural Fly Repellents
Certain natural scents and products deter flies from an area, acting as indirect natural enemies. These can make areas less inviting to flies and reduce chances of infestations. Some common natural fly repellents include:
- Mint oil
- Citronella
- Eucalyptus
- Basil
- Bay leaves
- Lavender
- Lemongrass
Planting these sorts of aromatic plants around outdoor living spaces help deter flies without the risks of chemical pesticides.
Parasitic Nematodes
Certain tiny parasitic roundworms known as nematodes can also be used to kill fly maggots and larvae. Species like Steinernema feltiae enter fly larvae and release symbiotic bacteria that poison the developing flies. The nematodes multiply inside the dead larvae and emerge to seek new hosts.
Applying these beneficial nematodes to manure piles, compost bins, and other fly breeding grounds can break the fly life cycle and prevent new adults from emerging.
Pathogenic Fungi
There are also predatory fungi that attack flies. For example, Pandora neoaphidis is a naturally occurring fungus that infects and kills house fly adults. Fungal spores attach to flies and penetrate the exoskeleton. The fungus multiples inside, eventually taking over the fly’s body and causing death.
Applying fungal-based biopesticides can reduce fly populations in areas of heavy infestation. The fungi carry over between generations, infecting new larvae and flies that come into contact with remains of dead infected flies.
Fly Diseases and Parasites
Along with predatory fungi, flies suffer from viral, bacterial, and protozoan diseases and parasites that hamper their survival and reproduction, including:
- Gregarines – Protozoans that infect the fly digestive tract.
- Parasitic wasps – Various wasp species that lay eggs in fly larvae and pupae.
- Mites – External parasites that feed on fly hemolymph.
- Nematodes – Some roundworms parasitize fly larvae.
- Hairworms – Parasitic worms that mind-control flies.
These pathogens and parasites can shorten fly lifespans, reduce egg laying, or even manipulate fly behavior. Their complex life cycles often involve multiple flies across generations.
Competitors
Flies also compete for food and breeding sites with other fly species and insects. This intraspecies competition limits fly populations. For instance, one house fly study showed:
- When alone, female flies laid over 100 eggs per day.
- When grouped with other female flies, they laid only 20-60 eggs per day.
Having other fly species and insects around creates more competition for survival. It thereby reduces the reproductive potential of any one species, like house flies or stable flies.
Predatory Avoidance
Flies have evolved various ways to detect and evade predators. These include:
- Quick takeoffs – Flies can escape danger incredibly fast.
- Erratic flight – Flies uses quick zig-zag and up-down patterns to escape predators.
- Detection – Sensory hairs alert flies to nearby predators.
- Resting spots – Flies avoid open areas where predators can easily spot them.
- Playing dead – Some flies feign death to avoid attack when captured.
These and other behaviors reduce flies’ risk of being caught. Predators have to adapt their own strategies and senses to counteract flies’ escape abilities.
Habitat Reduction
While not a direct predator, humans can alter conditions that impact fly survival. Steps like:
- Removing food and water sources
- Cleaning up fly breeding sites
- Sealing entry points into buildings
- Installing fly light traps
Can make areas less hospitable to fly infestations. In conjunction with natural enemies, reducing fly habitat availability helps limit populations.
Conclusion
Flies face threats from all sides in nature. Spiders, insects, amphibians, birds, and other predators keep fly populations in check as part of the ecosystem balance. Parasites and pathogens also hamper fly growth and reproduction. While no one method will eliminate all flies, combining biological control and habitat modification provides the best defense against fly outbreaks.
Encouraging natural fly predators allows nature to run its course and control flies without excessive pesticide use. Targeted sanitation and trapping offer additional ways to tilt conditions in people’s favor. An IPM approach that uses all available strategies is key to warding off bothersome flies.