3. Infection
The only other time you might confuse a bite from a house spider with one from a black widow or brown recluse, is if it causes an infection.
This occurs when bacteria gets into the open wound, thereby causing the body to react to try and drive it out. You might notice that you develop a rash, that the surrounding area becomes discolored (perhaps blue, black or yellow) and that the entire limb becomes painful to use.
You might also once again notice symptoms of a fever and in this case you will likely need a course of antibiotics. Once again, it is worth visiting your GP in either case.