You realize this is a bit like asking where do people come from.
Recluse spiders can invade homes, but black widows seldom come indoors, they hate human activity.
Spiders are arachnids so they are related to lobsters and crabs (all have 8 legs). Since spiders have relatively soft bodies, it is rather rare to find spider fossils. You should check out Wikipedia for spiders, Wikipedia is a great resource for info like this.
Don't listen to Batman there. They totally grow from a mold. So anywhere that collects moisture like the insulation in your attic, or in your walls, can grow this mold. Its different for every kind of spider. Some even grow in the tank on the back of your toilet, and under sinks. Because of this Spiders are drawn to moisture. That is why people wake up with them on them all the time. They are attracted by the moisture leaving your mouth as you breath in your sleep.
But don't worry Brown recluse spiders can only make an adult sick not kill you. The best way to get rid of all the spiders in your house is easy. Go into your attic and disconnect all the big silver vents from your unit. then turn your thermostat to heater. This will turn your attic into a hot box and force all of the moisture in your insulation to evaporate. Thus killing spider mold and solving your spider problem.
What?! Are you serious? What do you think lays the eggs that spiders come from? Birds? Cows? People?
Well that depends
When I was a professional yodeler, back when there was still high demand in the job market, i poured orange juice into a hole in the ground. I then took a tree sapling and stuffed it in there too. A spider came crawling out and pooped gold. I was so freaked out i killed it, and then God came and gave me a lecture on the mathematical implications of having a face.
Did spiders come from plants or trees that created them from moist environments? I know that they hatch from eggs but they must of came from somewhere; We got brown recluse spiders and black widow spiderrs and I don't know how they manage to get in ones house. I already know that they come from cracks and any small openings but I don't know how they were created other than the spider eggs.
