(Julian Smith/EPA)

Consider the housefly, trying to land on your lunch, its wings beating so rapidly they make a buzzing sound.

Compare that with the stately heron, arcing its wings as it lifts gracefully into the air and flaps slowly, silently away. Two completely different patterns of motion: It’s amazing that both produce flight.

What may be more amazing is that some animals can fly at all, while gravity tethers most species firmly to the ground. David E. Alexander explores how that came to be in a new book, “On the Wing: Insects, Pterosaurs, Birds, Bats and the Evolution of Animal Flight.”

A scientist specializing in biomechanics at the University of Kansas (and a radio-controlled airplane enthusiast), Alexander wanders animatedly through discussions of the four types of animals in his title, serving up fascinating facts and unanswered questions.

Insects developed flight at least 300 million years ago; bats, the newest fliers evolutionarily speaking, didn’t show up until about 65 million years ago. The keratin that makes up a bird’s feathers is found in human skin but nowhere in insects. Unlike humans’ in-and-out breathing system, birds have a unique flow-through, one-way lung that provides an astonishingly efficient supply of oxygen.

Alexander discusses lift-to-drag ratio, how flapping creates thrust, gliding vs. soaring vs. hovering, and the theory that wings evolved from gills. He points out how little we know about pterosaurs — exactly how they took off and landed, or even how heavy they were. (Estimates of the weight of Quetzalcoatlus northropi, the largest known pterosaur with a wingspan the equal of a Piper Cub’s, range from 150 pounds to — wait for it — half a ton.)

It’s not always the easiest reading for nonscientists, but it’s dependably engaging — and it has an easy-to-use index if you’re curious about, say, why the great auk couldn’t fly.