Curious:
I've noticed several large spiders recently--inside my house! Are they coming indoors to get warm?

Minx:
A common myth is that spiders come into houses in the fall to get out of the cold. But according to a spider expert,* "house spiders are usually not the same species as the yard or garden spiders outside the house."
"If a large number appear at a specific season, it is usually late summer (August and September)--not a notably cold time of year!--rather than fall, and their appearance coincides with the mating season of the given species. What you are seeing is sexually mature males wandering in search of mates."
*Rod Crawford, Burke Museum
http://www.burkemuseum.org/spidermyth/myths/comein.html