Let's say for this case, i'd GUESS spiders are Insects, and desert mobs are desert mobs.
Just cause two different mobs spawn in same map doesnt mean they are affected by something else.
In that case Animal works on ogres.
Orc works on snakes/outlaws in valley (45 metins).
Animal works on Lycans.
Well you catch my drift. Hope it was helpfull, tho i've been wrong before.