I wonder if maybe he is just upset that youre holding the cup and he feels watched? I know chameleons are very sensitive when they eat because they need their eyes on their food and not looking around for predators etc.. I would suggest getting some fishing line string and tying a plastic cup or something of that sort to tie to the screen cage, thats what I did. I have also seen people make their own feeder cups where the insects can climb up!
such as this: