Again be prepared for spoilers!
*** Spoiler - click to reveal ***After you meet with Cleopatra (Also unmissable) you are given four new animal related targets to hunt. Now they can be done in any order, but as the Scarab is the easiest (at level 15) it makes sense to do his first.
Travel to Letopolis and go through a rather enjoyable quest chain. You'll know you're near the end when you get buried up to your neck in sand (Hold to summon your horse to get you out, the game had to tell me this because I couldn't figure it out). You reclaim your gear then kill the Scarab.
After the cutscene plays out you will get your achievement.
Let's keep cheevin' together