We have two types of large meal worms - Giant meal worms and super meal worms, one of which (at least over here) are a different species to regular meal worms, and they are fine to feed to your herps! (Size of the herp permitting). We feed our adult dragons giant and super.
Meal worms in large quantities are not really the best staple as part of your reptile's diet, because of the hard exoskeletons and their phosorus:calcium ratio is quite high, so you should provide a supplement and balancing food stuff.
Temperature is a factor which features in the slowing down of the pupating stage of the giants.
There are many myths and claims about meal worms - one is that meal worms, even regular ones, are dangerous to small reptiles as they can stay alive in the gut and eat their way through the animal, ultimately causing death. I'm not aware of any documentation that supports this claim (anyone??). Another is this claim that the large ones are dangerous to your reptile. I don't believe this, we have always fed them to our dragons with no problem, but if any documentation ?? shows this claim to be true then ofcourse I would take it on board.
What animal are you intending to feed them to, and how large is the animal?
*Edit : The lack of movement you talk about with your large meal worms may be due to the temperature or their age? Ours have always moved about as the small ones have.*
