Dunno if mobile bug or wot but I noticed if u hit them in a certain spot you take damage. No it wasn’t biting or spitting, I tried on pachyrhino and it took damage every time it hit it. It was on passive
Not exactly the best combat mount, slow, stamina isn't the best, a little squishy. But a few high levels of these on base defence are pretty good. Put a few in the inner parts of your base (along with the spiders to slow them down) and the will have your enemies armour being melted in seconds!