Black Widow Infestation?

When we were setting up a pool and moved the greenhouse we found a black widow spider crawling up the side. Then we found one in the dirt, then one on the ground, and another one on the side. Why are there four big black widows in my greenhouse? It's not a greenhouse, more like a box with dirt where I grow plants. I don't see an eggsack anywhere. How do I get rid of them? What shoul I do?