What kind of spider is this?
Hi, this is a male Black Lace-weaver, Amauroubius ferox. 🙂
Are they dangerous?
They’re not considered to be of medical significance. My only concern with them being in a basement would be whether or not there’s a chance one could find it’s way into laundry. They’re only likely to bite in self defense. You can reduce the number of spiders you find indoors, by sealing cracks around floors, doors, windows, foundation, etc., vacuum everywhere and empty the canister outside.