Can be found in Carno island cave, south west lava cave, south east cave near Stonehenge, Central cave near volcano, and possibly others. They are very rare spawns but if checked regularly you can encounter them if looking to tame.
When i was exploring the island map i saw the chitin cave. I wasn't ready for the cave and i had to run out because i ran past 3 of these things. Good thing it was daytime. Go in the chitin cave during the day just saying