Black spider with white sack?

I have a ditch next to my house with a lot of large rocks in it. When I was moving the rocks, there was a black spider with a white sack on the back of it-almost like eggs. When I killed it though, nothing came out of it. The more rocks I moved, the more I found, so I don't think it's a mother spider, or is it?

Answers:
Did it look like this?

What is shoe polish made from and why does some shine more than others like Parade Gloss?

How long does it take for a rat to decompose?

What can I put down to prevent weeds and grass from growin before my above ground swimming pool gets installed

how much money would a person need to live a middle class lifestyle without working?

What state has the most trees?

Home And Garden Party Help?

How can i tell if my boyfriend loves me?

Anybody got coupon for Graber blinds?

I own a spider within my house to be precise scarlet colored. It is something like the shape/size of a loner. What is it?