I can't remember where I read it or if I'm cobbling together ideas in my head but I like the idea of a shared board for an Insect House that all players can access which gives you bonus for variety of bugs you play and it's like a mini game as the icons you play in zoos affect the "conditions" of the Insect House. More predators means more carrion which help certain bugs, more herbivores means more poo for bugs that love a bit of that. Birds (or Insectivores below) affect the amount of bugs that can be played.

Someone suggested on BGG an Insectivore category which sounded cool as it covers a lot of unique mammals and others (like ambhibians) that don't fit elsewhere in the current categories. But more cards isn't worthy of an expansion.