There are about 35 species of Scorpions in Arizona.  Although all are venomous, only the Bark Scorpion which is the most venomous species in North America is considered an issue medically.   While anyone could have an allergic reaction to a scorpion sting (just like with bee stings) there has been no recorded death due to scorpions in Arizona in the last 40 years.  

Scorpions are nocturnal and generally dormant in the winter, so most active at night during the summer.  They ordinarily eat crickets, roaches, beetles and other small insects but can go 9-12 months without food.  

Bark Scorpions are small, 2-3 inches full grown including their skinny tail, have an average life span of 5-9 years and are typically yellow-tan in color.  Scorpions are arachnids, like ticks and spiders, with 8 legs and 8 eyes and are great at climbing walls and trees.  They can fit through a crack only 1/16 inch wide (about the size of drain holes in door and window frames) and love to hide in Mesquite tree bark and under palm tree fronds.