How do I effectively use flying demons?

[earwicker7]

It's my first multiplayer game, and I was kind of planning my strategy around using summoned flying demons. So far, in the battles I've had, they are usually the first to die even though they are the strongest troops.

Are there any general tips to using them effectively? Do they have to be used in overwhelming numbers (this may be part of the problem, as I usually can't afford many of them)?