Their webs have no patterns on the web and are very strong. If you put a twig through a black widow spider's web, it will stretch and you can hear it break. Black widows spread by hatching and use their web as a hot air balloon. They easily attach to areas all around the house.
They spend most of their time on their web and can even build a web on an area that has just been sprayed with pesticides. Proper identification and frequent free retreatments will help in keeping them outside your property.
Black widows produce a neurotoxin which causes severe cramping in its victim and can be fatal for the young and elderly. Getting rid of these spiders calls for specific treatment protocols and is a job best left to professional pest control contractors.