Some animals took to the skies long before the advent of wings.
Flying without wings. I’m Bob Hirshon and this is Science Update.
Birds, bats, and insects may rule the skies, but as any skydiver knows, you don’t need wings to fly.
They’re controlling the aerodynamic forces; they can initiate spins, rolls, tumbles, and really control their body posture to great accuracy in midair.
That’s UC Berkeley physiologist Robert Dudley, who studies the evolutionary origins of flight. He says like skydivers, many insects also maneuver through the air without wings, or only partial wings.
They can use different pieces of their anatomy to effectively generate and control the aerodynamic forces.
Dudley’s research on primitive insects has demonstrated that the physiological adaptations used in powered flight occurred well before the evolution of wings.
We think of flight as being rare, but if we think of flight as controlled aerial behavior, it actually may be very widespread in the animal kingdom.
I’m Bob Hirshon, for AAAS, the science society.
Making Sense of the Research
There are many types of animal locomotion, or movement, such as swimming, gliding, galloping, hopping, crawling, or flying. When animals move through the air, it is known as aerial locomotion.
Scientists divide aerial locomotion into two categories: powered and unpowered. In powered flight, an animal uses its own muscular power (such as from the flapping of wings) to generate aerodynamic forces (forces exerted on a body by the air). This is traditionally what is called flying. In unpowered flight, however, the animal does not use its own power to fly. Instead, it relies on aerodynamic forces exerted on its body by the wind or by falling through the air. In these cases, the animal will often use controlled aerial behaviors, such as gliding, to assist the process.
The evolution of flight is a topic of great interest to biologists. Although many biologists consider flight a rare form of locomotion, controlled aerial behaviors are much more widespread. Robert Dudley and his colleague Steve Yanoviak, a researcher from the University of Louisville, study a form of unpowered flight used by wingless arthropods. Their results suggest that flight first began through stages of gliding and maneuvering in earthbound arthropods like ants. This also suggests that controlled aerial behavior preceded the origins of wings in animals.
For example, an amazing variety of animals have learned to glide through the forest. They range from flying squirrels to flying lizards and frogs, and even snakes! Gliding ants—the only wingless insects known to actively direct their fall—were first observed last year outside Iquitos, Peru, by Yanoviak.
These amazing ants have a more flattened head to slow down their fall, while the hind legs and abdomen act as a parachute and steering wheel in order to make changes in directions. Living in the tree canopy of Argentina and Panama, gliding ants spend most of their lives running up and down the tree in search of food. And if they ever find themselves in a free falling situation, they manage to glide back to the tree.
Dudley discovered that during the controlled descent, at speeds above 4 meters per second, the ants perform “rapid postural adjustments,” Dudley says. “The limbs are moving, it’s not like a paper airplane.” It seems that hundreds of species of tree-living ants have evolved this controlled gliding, perhaps to avoid falling to the ground and getting eaten by a ground-dwelling ant.
Now try and answer these questions:
- Why does Dudley say that flight might not be as rare as we think?
- What are some of the differences between winged flight and unwinged flight?
- Why does Dudley believe that controlled aerial behavior came before the origins of wings?
You may want to listen to Insect Gears, where you can learn about how some insects’ legs have gears that look and function like the classic man-made invention.
You also can go to Flight without wings, from the Why Files, to learn more about the tree-living ants that can glide.
In addition to the resources mentioned, you can extend the concepts in this lesson by helping your students explore the role that variation within a species plays, which is to maximize survival of some members under changing environmental conditions, in Feathers: The Evolution of a Natural Miracle.
In Periodical Cicada Survival, students explore defense mechanisms involved in predatory/prey relationships.