I personally have not found this to be true in my observations.In fact, the HL's that I have purposely eat some sand/gravel now and then, so for them to get a little with an ant is not an issue.If the ant is clamped onto a stick or twig it can be a problem as even a blade of grass in there (hl's) mouth seems to upset them terribly.
I took one of my HL's to a vet once and she said to put them in an enclosure free of sand, so as not to ingest any while eating. I said that I had seen them "eat" sand on purpose, and that it did not bother them in the least.................scott