In my life I got bit by a spider once when I was around 25 and three times while I have been 61. Something is happening around this place. The bites are noticed after I rummage around under the back porch. The bottom of the porch is about three feet above the ground. In that place I keep a wheelbarrow, lawn mower, lawn chairs, the loading ramps for the trailer, bike parts, and other junk. The crawl space used to be dirt. A few years ago I covered it with red bricks. There is no mortar between them. Just some cracks and crevices.
Some spiders spin webs and wait for prey. Others do not have webs. They wait hidden from view and ambush their dinner when it gets close. We have venomous spides of both types in Oregon.
What I am learning, from experience of the wrong type, is to pave crawl spaces or leave them dirt, wear gloves and knee pads when in them, and to toss in a pest bomb before entering. It prevents "spider finger."