Studying bird flight and insect flight: Would studying aerodynamics of airplanes be useful? Would studying the aerodynamics of airplanes be useful, if one wants to study bird flight and insect flight?  

For instance, would studying a gliding paper plane and a gliding unpowered airplane be fundamentally the same?  

I've read that aerodynamic laws for airplanes are different from aerodynamic laws governing bird and insect flight, but I forgot where I read this from -- possibly from an academic journal paper, if I remember correctly.
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.