To start, you will need to make a well. To make the bricks, I created several wooden frames from 1.5 x 3/4" boards from Home Depot as shown in Figure 1. I cut and glued cardboard to the frame. The front of the frame was 1.5 feet by 1 foot.
There is no need to create a complete box with the frame, just the front, top and parts of two sides. Make a mixture of water, flour, Elmer's glue and decomposed granite or other rocky soil. I used 3 cups water to one cup flour to one medium-sized bottle of glue to one handful of dirt. The dirt/granite gives texture. You might play with the components to get the right consistency. Now, dip paper towels or newspaper in the mixture and cover the cardboard panels. Once dry, paint with a stone-colored spray paint. I made two layers of bricks and used a stiff needle and thread to attach the bricks together. I made the well into a semicircle that was four feet in diameter and two feet high. Use a misting of flat black spray paint along the edges of the bricks to add realism.
I wanted fog to raise up from the well, so I placed a small stool in the center, then covered the top of the well with a loose-fitting sheet of black painter's tarp (but attached it from the inside so it was not visible). I placed a pot of water on the (covered) stool and put in a Mist Maker from mainlandmart.com. The purpose of the plastic tarp is to help hold up the mist so that it spills out over the top of the well. The Mist Maker is not powerful enough to fill the well so the plastic is necessary for the effect.
For the back of the well, I painted a 4 foot by 6 foot foam board panel (Home Depot again) which I attached to a frame made of two by four boards. I needed the support of a heavy wood frame because I hung a two-way mirror above the well. This way, I could hide behind the wall to operate the spider and still easily see the kids. I bought that mirror at Spencer's Gifts on November 1 a couple of years ago at a big discount. It was not a two way however. So, I looked up a glass house in the yellow pages and asked them the custom build a 12" round two-way mirror. That cost me, surprisingly, only $15. Well worth it.
Sorry for the after-the-fact pictures here. To make the spider's head, I got a large sheet of styrofoam, cut it up and glued the pieces together into approximately the shape I wanted. After the glue dried, I used a knife to smooth off the sharp corners a bit. Note of caution, shaving styrofoam makes a big mess. I did the same for each mandible.
I worked on the mandibles first. After shaping the styrofoam, I covered it with a thin layer of paper mache (water, glue, a little flour and newspaper). This allows for a smooth, paintable surface. I thought about gluing fur onto the mandibles but I decided that if I put fur on those, I would have to make the whole thing hairy. I made the fangs out of Skulpey sculptor's plastic (available at art shops). I incorporated a section of coat hanger wire into the fang to help attach it to the mandible. Some glue and paint and the mandibles are ready for the main head.
I glued the mandibles to the main head, then covered the head with Great Stuff spray foam. After the foam dried, I carved out holes for the eye sockets. I used Skulpey for the small eyes and styrofoam balls for the larger ones. After attaching the eyes, I gave it another layer of spray foam.
I painted the base green and black then striped it with fluorescent orange. The eyes I made fluorescent yellow. Your done. "But wait," you say. "What about those legs?" That is next.
How to Make Giant, Candy-dispensing Spider Legs