They look like most spider egg sacks pear shaped light tan or yellow. Here is a cite with pictures and information for you... en.wikipedia.org 
What Does A Black Widow Spider Egg Sack Look Like?
Black widow spider was placed in jar - after 2 days - "thought" she was dead. Now after 2 months - found that she was still alive. I then fed her chicken & water, but going to release her. How was it possible? She mated before she was put in the jar - the male was "eaten". So how long can a black widow spider survive without food?
Its white, sometimes kinda yellow looking, and is round...you'll know it when you see it.
