R.J.
Those would be baby spiders. They're hatching right now all over the country. The egg sacs are found in odd places you don't usually see. Like WAY up in the corner joint of a ceiling (really hard to see white on white the size of a dime), underneath the cabinets, under shelves, in closets, along the baseboard behind things like bookcases and bedframes (although they tend to like up high places better). Part of my spring cleaning (around valentines day, and again a month later) is to search my house from top to bottom, in and behind everything... and then sic my husband on them (I HATE spiders). They wipe away with a paper towel at that stage (egg sac stage) but yucky yucky yucky yucky eeeeeeeeeeew. ((Did I mention I hate spiders?)
Like baby snakes, when they bite they release ALL their venom... but unlike baby snakes they don't usually have much. So if you get a reaction it's usually from a pretty poisonous species or you happen to be sensitive to it.
At this point, you *may* need an exterminator. But at the end of next winter, go on the hunt. You still can, as many may not have hatched yet. Even if they all have, you can get an idea of how many there are by the wispy bits that you find left (as in how many egg sacs, there are hundreds and hundreds of baby spiders inside).
Eeeeeeeeeeeew.