However, you could consider these options:
* Other animals: Since aardvarks are insectivores, you could say an antonym is any animal that isn't an insectivore, like a carnivore (lion) or herbivore (giraffe).
* General opposite: If you're looking for a word that's the opposite of "aardvark" in a general sense, you could say something like "human," "bird," or any other animal that's drastically different from an aardvark.
Ultimately, the best "antonym" depends on the context you're using it in.