Our water table is a bit high and I'm thinking that a root cellar wouldn't be so good, but I want one too. A neighbor down the street and around the corner put one in though and built a small building over it so that you have to go into the building to get to the root cellar. They lined the cellar with cinder blocks cemented together. I think the floor is cement but I would want dirt as long as it wasn't moist from water coming in through the soil. They don't seem to have any problems with it. They stored the potatoes they grew in it and the potatoes were still good in the spring. Their son has a backhoe and dug out the hole. They (they're a retired couple) did the cinderblock work themselves. It took a while but they got it finished. I don't remember seeing any spiders in there but there may have been some. If you don't have flies or any other bugs for them to catch they'll starve to death anyway. If you do have the other bugs, it will be good to have a few spiders to keep their population down.