danfrog is right, sometimes the size of the prey matters, my big girl would eat something big only, so for one nightcrawler she wouldn't bother, but give her 5 hanging tightly from tongs she'd be all right, but my pixie on the other hand loves crickets, that she'd eat like 100 at a time, very funny to watch how a big frog is chasing tiny in comparison prey all over the tank, sometimes catching 5 at a time and obviously having time of her life lol

how does he looks, healthy? you do vitamins, right? i'd write down a log for him for some time, record when/what/how he eats, cleaning, bath, anything at all that you do ( or he does) over a period of time. I keep logs like that for all my pets, in emergency it is easy to pull up records, it is very useful.