Page 266 - The Origin of Birds and Flight

264 The Origin of Birds and Flight

It is very dangerous for a pilot to bend perpendicular wings. As the
plane takes off, the air current acting on the wing finds it more difficult
to attach to the wing edge. When the current disappears completely,
the plane wobbles and loses height. On the other hand, this is an ad-
vantage for the fruit fly, because it does not have to maintain its wings
in one position. The fly beats its wings so quickly that the wings per-
form another movement by the time that the edge directing the flight
ceases to be in contact with the air current. At the end of every move-
ment, it rotates its wings around themselves, causing them to beat in
the opposite direction. This forms a vortex and no instability takes
place. 234
The fine channels in insects’ wings permit air and blood to flow
through them. 235 With flies, however, a great many additional details—
such as their sharp eyes, the small rear wings they use for balance, and