Studying bird flight and insect flight: Would studying aerodynamics of airplanes be useful?
The biggest factor, besides the basic insect ornithopter wing mechanics, is air viscosity effects, or Reynolds Number.  To insects, the air is extremely "thick" with extremely low Reynolds Numbers, and the optimal airfoils are single surface membranes - insect wings. As Rn gets higher, the desired airfoils get thicker (bird wings) and thicker until you are in very high speed flight and the wings have to start getting thinner again.

Anyway, for a basic overview of all of this, I can't recommend the book Miracle of Flight by Stephen Dalton highly enough.  It's a book for the layperson that illustrates flight pretty much up the Reynolds Number range, starting with insects, then birds, then the man-made stuff.