Arizona is unique in that it shares the same desert biome as Mexico and regions south rather than the usual American southwest desert biome, which contains a lot nastier critters than we normally have in the continental US, even apparently similar desert regions. As a result, there are species of snakes, spiders, scorpions, and other poisonous nasties local to Arizona that are substantially worse than what one normally expects in the US. I had a friend who almost lost a leg because he was bit by an Arizona recluse spider on the thigh.