Black snakes eat mice and other rodents. If it is hanging around it may be finding food, such as, mice and rodents. They are harmless and they do eat poisionous snakes as well. It's more afraid of you than you are of it. Best thing to try is call varment control. Seriously, there are people out there experienced in catching these guys. Another option would be to call your local Extension Agency they are helpful as well. But also check around your house's foundation for any cracks or holes in vents if you have a crawl space and have those fixed or plug them with steel wool they don't like it. Also, if you put lime around the foundation or area you've seen it hanging out snakes don't like lime either. Good Luck!