Natural History by Russel Barsh and Madrona Murphy

Flies outmaneuver birds, bats and nearly every other family of insects.  - Contributed photo
Flies outmaneuver birds, bats and nearly every other family of insects.
— image credit: Contributed photo

Few animals can fly. Even fewer can fly vertically, upside down, or sideways as easily as horizontal flight. But flies can. Flies outmaneuver birds, bats and nearly every other family of insects.

Although their fossil record goes back to the steamy swamps of the Permian period 250 million years ago, the Order Diptera underwent an evolutionary leap just 65 million years ago, about the same time as the first placental mammals. Most flies are younger in evolutionary terms than the birds and about as old as bats. They are far from being “primitive.”  And flies are 10 percent of all animal species on our planet.

The earliest insects and most insect families today have two pairs of wings: four wings altogether.  The term Diptera means “two winged,” and this reduction in number is a distinguishing feature of the flies.  Their wings are also shorter than other insects, have larger muscles, and can flex and twist, allowing flies to maneuver deftly as they plunge forward at 200 beats per second.  At least one group of flies, the Syrphids or flower flies, can also hover for minutes, seemingly motionless, rivaling dragonflies and honeybees.

Like modern jet airplanes, flies have small stabilizers on their bodies to balance them in rapid flight: the halteres, formed from flies’ lost second wing pair.  The antennae of flies are miniaturized to reduce aerodynamic drag, while the compound eyes on their moveable heads are enlarged and assisted by three tiny eye-like ocelli that give them 360- degree views of approaching dangers.

Mosquitoes and craneflies are some of the earliest flies, adapted to the wet, warm world of the earliest dinosaurs.  They lay their eggs in water and spend most of their short lives as aquatic predators, eating smaller animals before emerging for a few days of adult life and reproduction.  The appearance of angiosperms (flowering plants) in the Jurassic period created a great new opportunity for the flies: eating pollen and nectar.  Flies with stout bodies, long tongues for nectar sipping, terrestrial larvae (maggots) and longer adult lifetimes evolved side by side with the bees and wasps, to capitalize on a world filled with flowers.  Indeed while most flies are “cheaters” and visit flowers without pollinating them, some fly families (including “true flies” and flower flies) have bristly hairs on their backs and legs that make them relatively good pollinators.

Jurassic flies evolved another anatomical advantage: re-positioned reproductive organs enable flies to mate much more quickly, often while in motion, than other insects, so they are less likely to be eaten by birds, amphibians or other insectivores while they are distracted!

Now that many flies laid their eggs on land and developed as maggots, one of the key innovations of Jurassic flies was a hard protective case (puparium) that forms around the maggot when it is ready to begin its metamorphosis into an adult fly.  After the great extinction event that ended the “age of dinosaurs,” flies evolved a clever way of making it easier to emerge from the puparium: a tiny balloon in the fly’s head that expands and pops open the end of the puparium!  Compare the egg tooth of a hatching bird.

The descendants of this New Fly—the Schizophora (“higher flies)—are about a third of all living flies, including houseflies and fruit flies, and include families that are predatory and parasitic as well as plant and nectar eaters.  Nonetheless, many insects that we call “flies” are not even distantly related.  Caddisflies, for example, which provide winter food for trout and are among the most common “flies” tied by fishermen, are more ancient than Diptera and more closely related to moths!

Although Kwiaht has collected and photographed dozens of species of flies on Lopez alone, we still know very little about the diversity of flies and other insects in the San Juan Islands, or how they may differ from insects on the mainland.  Flies may serve important ecological functions here; for example, some of our late summer wildflowers appear to be fly-pollinated.  Some flies, moths and other insects actually emerge in winter and may be essential for the survival of bats.  And spring emergent insects are essential for early-arriving songbirds!

Learn more at and check for updates on local insect research.

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