Items, NPCs, quests, objects and spells of patch 1.12.1, read live from the realm itself.

Untested Scorpid Sample

NPC	Level	Zone	Chance
Scorpid Hunter	40 - 41	Tanaris	100%
Scorpid Tail Lasher	43 - 44	Tanaris	100%
Scorpid Dunestalker	46 - 47	Tanaris	100%
Scorpid Duneburrower	46 - 47		100%