Butterflies, Flight, and Physics

In “How Butterflies Fly,” J.N. Quinn writes:

The wings of butterflies, and indeed, most insects, have a sharp edge. The sudden cut of of a butterfly’s wing pushes air much like a spoon in coffee. In the case of coffee and creamer, swirls appear around a low pressure center; butterflies use the air in the same way. Their sharp wings swirl the air above their wings making a low pressure vortex. Thus the vortex sucks the butterfly higher and allows the wings to snap back into position with less resistance.
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With every beat of its wings, butterflies produce more than enough lift to keep it aloft. This over-lift causes the jerky, tumbling leaf motion associated with butterflies fight. The weird patterns butterflies move in makes catching them, for both birds and humans, more difficult.