Many people may find this difficult to believe, but that semi-arid zone stretches all the way up into my part of Canada. We get all the same critters that you just mentioned, except for the scorpions, where I live. Although, I have heard that they actually do get scorpions in a town about 140 miles south of us. The black widows live right in our yard, hiding in all the nooks and crannies.
It isn't uncommon for summertime temps to be 100 F and above, with RH %15-20. Remember, I am talking about Canada. Most Canadians don't even know we have a "desert".