I've been putting flies into the cage of my praying mantis, Morse (like Morse Code because of his habit of tapping on the side of the glass). I'm wondering if Ruud or anyone else can tell me if there's a better diet than flies for a praying mantis.

id feed them crickets or other insects u find around.the thing that sucks about keeping mantids is i guesse they only live for about 6 months or so.check out this website
www.arachnoboards.com
theres alot of info on here that should be helpful to ya

Mantids eat just about anything that moves. I had a big one last year that tried to take a bight out of my finger (i'm not kidding, it latched on with its claws and was trying to get it's mouth close enought to take a chunk out of me). It's best not to feed them te same thing over and over. I give mine a mix of flies, crockets, caty-dids, bees, and wahtever else i can find. I dont really give them spiders. Partly because spiders cna be annoying, and messy.
I've had mantids live for longer than 10 months when kept warm (but not hot, no direct sun). I have one little booger right now that i found on a bench in the garden section of a local Orchard Supply & Hardware. I guess they had some ootheca (mantid egg sacs) for sale, and one hatched. I've been feeding it aphids and gnats.
What kind of mantid do you have anyway?

Well, have is a past tense word at the moment. He died last week. It was a male mantis, that was all I know because this page said male mantis' wings extended beyond the abdomen and they were the only one that could fly.