Why are there so many spiders in my backyard?

Long webs strung from trees and bushes, from one to another, are the trails left by spider(s) traveling from tree to tree or tree to bush, etc. Since they can't fly, they spin out long threads, hanging from the trail end, waiting for a breeze to take them to a new location. Occasionally, you can see a whole bunch of them at once, crisscrossing every which way. That would be when a nest of spider eggs has hatched and the little Spiders are seeking a place to set up 'home'.