Though I don't entirely agree on the rarity of Larger Umber Hulks and Hook Horrors, Scarab Beetles are significantly more common and, consequently, their absurdly more powerful brethren. Stag Beetles and Hive Mothers having Thick Monstrous Chitin would be very helpful as, at the moment, the only reliable source of Chitin, thick or otherwise, is Har'Akir and even there it's somewhat of a rarity to obtain what you need most of the time. It would make a lot of sense as well since Hive Mothers have some thick freakin' skulls. I think I usually have to dish out a nice 150-200 damage to them every time I see 'em.