Air travel is one of the most regulated industries in the world. Yet somehow, nobody thought to ban emotional-support hedgehogs and spiders.

So the airlines are policing themselves. In a triumph of common sense, which can seem rare nowadays, American Airlines on Monday followed the lead of rivals Delta, United, and Alaska and imposed new limits on emotional-support animals. The move follows years of increasingly bizarre incidents in which passengers turned planes into airborne Noah’s Arks and tried to bring aboard animals including pot-bellied pigs, hamsters, and peacocks—to say nothing of untrained dogs, which occasionally relieved themselves or bit other passengers.