I've been living here more than 25 years and have never once had a negative experience with rattlesnakes or scorpions like so many people talk about. Either I'm just lucky or I'm oblivious.
Anyone who knows me puts their money on the latter.
Read an article some years back that said that coyotes are actually more common now than in pre-Columbian times. The loss of wolves as a competitor for food, and their adaptation to humans has helped their numbers grow by almost 5 fold.
That bit of info has really impacted my life philosophy.
Too dry for poison oak/ivy/sumac here in most places. Pretty sure I'm immune anyway. Dig through the exact same bush as someone else at the same time; next time I see them they're covered in rashes and calamine, but I never noticed a thing.
Never had problems with ticks here, but I know folks who have. I've used wood ash in my hair to keep them away while camping when I forgot bugs pray. Not recommended as a routine thing; ruins your sleek locks.
@rockm is right about their prevalence on the east coast, and I'll add fleas to that. Can't step under a tree without catching a tick, and a walk through the grass is like watching tiny black popcorn kernels.
Here cactus is a real concern for everyone. Get a barb stuck in your skin and it will fester fast. The super fine ones will stay in you for days, some times weeks. Those comfy hiking boots from the store practically attract the spines. Any off trail movement, and I recommend full leather with a heavy, hard sole.