Q: While watching hummingbirds with a friend, I saw a female bird eating what I call gnats. My friend said that hummingbirds eat nothing but nectar. Who’s right?

A: Hummingbirds do eat insects. Nectar (or sugar water) supplies them with energy but it is not a complete food source. Small insects, like gnats, mosquitoes and moths, are part of their regular diet.

see
http://www.worldofhummingbirds.com/bugs.php