I don't see a Balance thread, but I thought I would mention this - not a bug, though.
I think giving Giant Spiders and Baby Spiders Fear is a little overpowered.
In my game I was able to capture a few Giant Spiders with my Scout (it had the Courage promotion from a Lair/Dungeon event). Once I got them I was able to take out 3 AI civs because they could not attack the Spiders - assuming they could see them, of course. The Fear repelled them. The AI is woeful when it comes to getting Courage, especially early in the game.
Really, the only problem was again the Sabretooths that have Courage for some reason - maybe so they can kill your HN Spiders.
But once you get your HN Spiders into the territory of an AI civ, the Sabretooths are not a threat. You can easily take out early defenders leaving AI cities wide open for barbs like Goblins and Warriors.
Perhaps save the Fear promotion only for the top of the line Spiders, whatever that is.
I really enjoy the mod playing with all these animals (got a couple of Scorpions and Hyenas today), but have yet to find a solution to the Sabretooths which often spawn right next to my units and kill them in short order. Also, early in the game it is not possible to capture these beasts or you really could wreak some havoc in the game - good call there.
Maybe its time for Grand Menagerie 2.0
