Mad About Science: Flies

By Brenden Bobby
Reader Columnist

How many times have you suffered hours of torment from a lone, buzzing housefly persistently taunting you, landing somewhere on your skin and zooming away when you try to deliver it a one-way-ticket to the great dark beyond?

Such insufferable, infuriating, completely useless insects… Or are they?

Flies belong to the order Diptera, meaning “two-wing.” Many flying insects actually possess four wings, making flies somewhat unique in the animal kingdom. Dragonflies, butterflies and moths often have four wings masquerading as two, but there is no mistaking the two buzzing wings of a housefly.

The two wings of a fly are no accident. At some point in their evolutionary history, flies began to shrink a set of rear wings, which developed into rapid response and navigation organs that detect changes in air pressure, direction and tilt of the fly. These organs, called halteres, function as tiny gyroscopes that keep the fly oriented while performing highly acrobatic aerial maneuvers.

You may have noticed that it’s really hard to swat a fly with your bare hands, yet slapping them with a plastic fly swatter is easy as pie. Houseflies are covered in tiny hairs that are extremely sensitive to changes in air pressure. The insects can actually feel the air being pushed by your hand and react accordingly — zipping out of the way just before danger strikes. Fly swatters are designed in a checkered pattern to reduce the amount of air being pushed, defeating the fly’s ability to monitor air pressure and instead transform into a splotch of hemolymph (bug blood) strewn across your countertop.

Diptera is an immensely large order of insects with more than 1 million species of fly. Among these numerous species are the common housefly that you’ve likely encountered, as well as the infuriating mosquito whose females have made themselves annoyingly present this summer. Female mosquitoes drink blood from vertebrates but males do not. Both males and females eat plant matter and nectar. The blood they love to steal from us contains a large amount of sugars, lipids and proteins, the latter of which is used to help create clutches of eggs the females will deposit in or along the edges of stagnant water, in some cases creating a raft of eggs that will spawn many larval mosquitoes.

A common exclamation I’ve heard from kids at a number of science programs at the Waterlife Discovery Center is: “Look at all the tadpoles!” Unfortunately, they are not tadpoles. While there are many macroinvertebrates dropping eggs and larva into the water, a vast majority of these little wigglers are certainly mosquito larva, which feast on algae before pupating and eventually transforming into the winged parasitic pests we all love to hate.

Many flies follow a similar life cycle as the mosquito, beginning as eggs that hatch into a larval stage and then pupate in order to become a fully grown fly. The larval stage of many aerial and terrestrial flies is that of the maggot, a revolting and juicy little worm-like critter that feasts on protein often found in dead and decaying creatures. Certain kinds of maggots actually serve three very important functions for human beings.

Maggots have been historically used in medical fields for the process of “debridement,” or the removal of damaged or dead tissue from a wound. This means maggots are poured onto a festering wound and allowed to go to town eating all of the dead flesh. Once their job is done, they’re flushed out and the wound is sanitized. Debridement sounds disgusting, but it has been proven to reduce the chances of a patient suffering from sepsis and aid doctors in cleaning wounds, particularly burns that cover a large area of the body.

Maggots are also effective at reducing disease in the wild and in urban environments alike by devouring decomposing protein like roadkill — if left to fester, dangerous bacteria can experience explosive growth and the potential to infect other life through ingestion or spilling into waterways. Maggots stem this potential by eating the bacteria’s food source. Granted, flies can still spread dangerous bacteria, but the concentration of danger is reduced by being spread among hundreds of insects as opposed to one large mass.

Maggots are also a great lure for other animals, primarily fish. This has the additional benefit of being an economic driver in some areas of human society, allowing for people with relatively few resources to create a market for fishing bait to sustain themselves or their families. 

In some cases, maggots can also be used to aid the composting of materials, but this is more often done with species of beetles that break down plant matter, rather than protein-devouring maggots.

Some species of flies are masters of disguise. Flower flies will often masquerade as bees or wasps with alternating banding of yellow and black to deter predators. You may have seen one of these flies hovering outside during spring and summer. At first, they appear to be a bee and may instill a certain cautious and fearful reaction, but their flight pattern is markedly different from bees due to how they’re built. Flower flies are very skilled at hovering flight, while bees and hornets tend to make arcing swoops. Flower flies are harmless to humans and they help pollinate flowering plants, so try to resist the urge to smash them into the great dark beyond whenever you see one.

Stay curious, 7B.