So you live in a neighborhood here in the desert. There's a lot of houses and not a lot of desert anymore and you have scorpions. How'd they get there? A lot of people think that they came from the desert, and sometimes that's true but more often than not, they come from potted plants that you buy from your nursery.
Nurseries grow all types of varieties that you buy to plant around your home. Scorpions will burrow down into the actual dirt. Now this is an example of a dead tree, but for example purposes you can see how a scorpion can crawl into any area here while the tree's alive and well watered. Lots of crickets, lots of roaches also exist in this environment, so the scorpion populations thrive in the nurseries and then you take it home and you plant in the ground.
So you have one or two scorpions, but if those scorpions are pregnant or if they find other scorpions, they can develop a population in the middle of the subdivision, and it will grow exponentially because of the water and the drip systems at the base of your plants from that point they move into the house.