Object Overload has shown to have animals from real-life roaming the plains of Animania
Insects
Ladybugs
In In Deeper Waters, Tiki was playing a game named "What do You See." The bottom head spotted a ladybug in the grass.
Repties
Snakes
In Lost and Found, a venomous snake (possibly an eastern green mamba) appeared and bit Candy's arm, even though it was kicked by her. It is unlikely it bit Popcorn too.