The chances of a black widow fucking you up badly are slim to none. If you're old, or if you're a young child, you may want to be careful...but if you're a healthy young adult, black widow bites may cause issues, but chances are it won't be life threatening.
For your info, go to
http://www.emedicinehealth.com/articles/6436-1.asp
The only four spiders that are known to be dangerous to humans are brown recluse, black widow, hobo or aggressive house spider, and the yellow sac spider. There are 20,000 species of spiders, 60 species are capable of biting humans, most spider bites don't even break the skin. While spiders give me the fuckin chills, they don't scare me to the point where I hyperventilate because I know they aren't going to kill me.
Oh, and try SQUISHING the spider with your foot, or in a tissue so you can flush it. RAID usually only works on Ants, fleas and ticks...most bugs, as I have discovered, are immune to that shit.
http://www.emedicinehealth.com/Articles/10729-1.asp