They can become impacted when the insects are too large,[ usually babies and juveniles would be affected] also if not enough water is provided, and if the temps. are too low for digestion. Also, from eating the calcium type sand [ which shouldn't be used at all ] or other loose substrates....wood chips, etc. I would imagine that if the veggies you are feeding were thick and woody, like stems from broccoli, or thick slices of carrot, etc, you could also have a problem.