They live low and high, and because many people move from state to state, just about any kind of spider can be transported through a moving van.
Some spiders can bite humans and cause severe physical reactions.
They spread disease and contaminate food in our homes. Most flies lay their eggs in manure or rotting garbage. They can live in your wall voids and attic spaces for long periods of time. They are attracted to light and come down through recessed lighting in your ceilings.