Excluding the northeastern and upper midwestern states, scorpions are present across most of the US and just over the border into southwestern Canada. Although they can be found in a variety of habitats, many live in hot and arid deserts. Of the 90 or so species in the U.S., all but four naturally occur west of the Mississippi river with the highest concentration in the desert southwest. Most are terrestrial, living under objects on the ground or in burrows, but some are arboreal, meaning they live up in trees.