Fantastic Flies!

House fly.

House fly.

The Order Diptera (true flies) are one of the most amazing and diverse groups within the Class Insecta. They not only have a wide range of appearance, from metallic greens and blues to dark grays and blacks, but they are mimics, predators, pollinators, recyclers and everything in between. Have you ever noticed how flies are named? The “fly” portion is actually separate from the rest of their name, like house fly, blow fly or hover fly. This is a unique naming convention which separates them from other groups with the “fly” in the name like dragonfly or mayfly. So, any time you write down the name of a true fly, make sure the “fly” is separate word.

House Fly.

Fly with halteres circled. Photo by Antušek, Ivo / CC BY-SA

There are approximately 110,000 described species of true flies found worldwide. The Order name Diptera is derived from the Greek (di = two and -ptera = wing). What makes a fly “true” is one pair of wings and that the second, or hind, pair of former wings are modified into specialized structures known as “halteres.” The halteres are small ball-and-stick looking organs that act as gyroscopes and give flies the ability to be the most dynamic of fliers in the Animal Kingdom. Flies have a complete lifecycle, meaning they have four stages of development: egg, larva, pupa, and adult. They are also unique in development: the last larval skin has evolved to enclose the pupa in the Stratiomyidae (Soldier Flies) and within the Cyclorrhaphous flies, where it is known as a puparium.

Although many people associate flies with filth, they are extremely beneficial in all their niches.

Bee-mimic hover fly.

Bee-mimic hover fly.

Many flies are successful mimics of bees and wasps, like hover flies (Syrphidae), bee flies (Bombyliidae), and robber flies (Asilidae). This mimicking ability helps them in their survival, with warning coloration as a false “I’m dangerous” visual. Most Syrphids and Bombyliids are not only excellent mimics but are also efficient garden predators as larvae of things like aphids and caterpillars, where Asilids are also excellent predators as adults.

Tiger Bee Fly staking out nesting sites of carpenter bees.

Tiger Bee Fly staking out nesting sites of carpenter bees.

One species of bee fly that you actually would want to see around your house is Xenox tigrinus, the Tiger Bee Fly. This is the parasite of the carpenter bee (Xylocopa spp.), which causes such consternation to homeowners. The female hovers and finds a carpenter bee nest, where she lays her eggs, then the fly larvae eat the larvae of the bees; the newly pupated flies emerge the next spring to repeat the cycle on new carpenter bee nests.

Ceratopogonid fly on harvestman leg.

This ceratopogonid is a close relative of chocolate flies.
Pictured on harvestman leg. Photo: Matt Bertone/NCSU.

Flies as pollinators. If you are someone who likes chocolate (and who doesn’t!) you should be thanking flies. Only one type of fly, Forcipomyia sp., pollinates the flower of the Cacao Tree (Theobroma cacao) in its natural environment. The aptly named chocolate fly is in the Family Ceratopogonidae, the same one that includes the biting flies we call “no-see-ums.” This fly needs the rich wet humus of the forest floor under the trees to develop as a larva, then as an adult feeds on the nectar in the flowers, and subsequently pollinates them. The tiny midge is small enough to get into the flower for effective pollination. The adult flies form mating swarms at dawn and dusk, which perfectly coincides with the times that the cacao flowers are open. Co-evolution is fantastic!

Some plants like Jack-in-the-pulpit (Arisaema triphyllum), Skunk Cabbage (Symplocarpus foetidus), and our native Pawpaw (Asimina triloba) along with certain types of fungi (known appropriately as stinkhorns) have evolved to smell like rotting flesh to attract flies to pollinate (plants) or spread their spores to new areas (in the case of the fungi).

Black Soldier Fly depositing eggs on cardboard.

Black Soldier Fly depositing eggs on cardboard. / CC BY-SA

Flies as recyclers.  Many flies get a bad rap as squirming maggots on rotten, nasty things, but if it weren’t for these efficient recyclers, we would have a major issue underfoot.  Many types of flies lay their eggs on freshly decomposing materials, which helps break them down for successive decomposers.  One of the most efficient recyclers is the Black Soldier Fly, Hermetia illucens (Family Stratiomyidae).  The larva of the Black Soldier Fly is an excellent alternative to red worms in the compost bin, due to the fact that they produce an antibiotic to keep the bacteria at bay but also are efficient predators of other invasive insects in the bin.  Once the flies mature to adults, they will remove themselves from the bin (no culling necessary), reproduce, and re-populate the bin with more offspring.  If the population gets too high for your liking, the larvae and pupae can be removed and used as fish or chicken feed (pure protein!).

Lucilia greenbottle blow fly

Lucilia greenbottle blow fly. Photo: Matt Bertone/NCSU.

The Crime Solvers! Also in the niche of decomposers and recyclers, the flies (along with other insects) actually help us solve crimes through the field known as forensic entomology. Many fly species are compelled by specialized cues as to where, when and at which stage of decomposition they will lay eggs on a host. Some flies will only lay eggs if the source is in a protected environment (like a house), while others will only lay if it is outdoors. Blow flies (Family Calliphoridae) are the first to the party. They received the name “blow fly” because of their ability to find fresh carcasses when they are first “blowing” or emitting the initial gasses from decomposition. All these factors, and many scientists working on patterns, have led to insects being a great source within forensics. By studying the number of fly life stages present, and other factors like ambient air temperature, the time and place of death can be more precisely estimated.



Flies are crucial to medicine as well. Dating back to the Renaissance, physicians noticed some soldiers who were wounded didn’t seem to get infected wounds. Medical personnel noticed that the wounds were actually infested with fly larvae (maggots) of the Family Calliphoridae! Upon further investigation, they found that the larvae not only ate only the dead tissue but also secreted an antibiotic which kept the bacterial infection at bay. This was noted by Napoleon’s surgeon and doctors during the Civil War and was used during World War II to help heal the wounds of soldiers fighting in the South Pacific. Maggot therapy is used to this day.

Soldier fly. Photo: Matt Bertone/NCSU.

Soldier fly bee mimic. Photo: Matt Bertone/NCSU.

Flies also represent some of the most beautifully diverse colors found among all insects.  Within the Stratiomyidae, there are 2,800 species, with a great many of them looking nothing like the other members of their family.  You have Stratiomyinae, some of which are yellow and black mimics of bees and wasps, and Pachygastrinae, which are tiny and iridescent black.  There are the Prosopochrysinae, that are long-bodied and sport bright greens and blues, and then there are some like the Clitellarinae, that have a bit of everything, from the not-so-brightly colored Adoxomyia sp. to the Flame-setae Clitellaria sp. to the gorgeous iridescent blue- or yellow-headed Cyphomyia sp.

Asian Tiger Mosquito. Photo: Matt Bertone/NCSU.

Asian Tiger Mosquito. Photo: Matt Bertone/NCSU.

And what about the little mosquito? Believe it or not, mosquitoes are actually true flies.  The name “mosquito” translates to “little fly” (mosca = fly; –ito = small).  Mosquitoes are unique in that they have an active pupal stage.  Most holometabolous insects are sedentary, but not dormant, in the pupal stage.  Mosquito pupae are also known as “tumblers” because of the way that they spin end-over-end to escape predators.  Most people do not like these small biting flies, but they are an extremely important link in the ecological food web, providing food for many organisms in their larval, pupal and adult stages.  Only the female mosquitoes bite and draw a blood meal; they require the protein in the blood for egg development.  The males, on the other hand, peacefully wait in foliage or sip nectar from flowers.

So next time, instead of concentrating on the negatives, let’s focus our lens on how functional and amazing these creatures really are. They are far more beneficial than any nominal harm or inconveniences. And when the insect overlords descend, you can say you have a true friend in the flies.