Bed spiders? Bed bugs? what is it?

Now long story short my significant other is living with me and my mother and since our house isn't quite huge i made him a room next to mine in the basement and it doesn't have walls, just sheets attached to hangers that are hung on the piping on the ceilling. Recently, he's been getting bites on his legs. They range from small to medium size(as far as bug bites go) depending on how much he scratched them and they also look a little swollen. He works a job where he has to cut gr all the time so he originally thought they were "chiggers" but he realized that new ones would appear during the night while he was sleeping. He then went to his other job that he works with his half brother who said he had the same thing all the time and that they're "bed spiders"? that they "live under someones bed and come out at night to burrow into your skin for warmth while you sleep" I didn't really believe this so I decided to do some more research and everything I've found says spiders don't behave this way especially not in my area (midwest). I then washed his sheets tosee if this fixed the problem and he still had new bites the next morning I tried to research bed bugs and those aren't likely because they're visible to the naked eye, and while I was changing his sheets i found no such bugs. Does anyone know what this is? Is it possibly not even a pest at all? Genetic? or does he need a new bed? He and his brother have the same beds they did when they lived together at their moms house, could old matresses be the culprit? Anyone?