A black garden spider that I have in my bottle habitat is also preying on the baby spiders, eating them for a nice snack. The garden spider and the environment limits of scarce food are controlling the population of the spiders.
Its cool to see how it is all working out. There are now 11 baby spiders left out of the original 38. The mom spider is also still alive. All together there is probably around 40 spiders including the garden spider. The picture is of the mom spider, up at the top of the bottle.