1 box cake mix - or use your own favorite recipe
1 (3 ounce) box Jell-O (green or red)*
1 can chocolate or fudge frosting
Black or blue food coloring
6 black licorice sticks
2 large gumballs - either green or the "eyeball kind found in
    gumball vending machines OR decorator frosting of any color

* Prepare Jell-O according to package and chill to set. Stir occasionally so that the Jell-O is lumpy looking rather than holding the shape of the bowl.

Bake cake in two 8-inch round cake pans according to directions on box or recipe. Cool completely according to box and remove from pans when instructed.

Slice one cake layer in half. Place one half of cake on foil covered cardboard large enough to hold the 2 cakes side by side. (A platter would work too if you have one big enough) Cut a circle out of the center of the other cake layer, leaving about 1 1/2 - 2-inch thick ring. Carefully place ring on top of the half layer. (You can put a thin layer of frosting or jam on top of solid cake to help hold the ring in place if you want, but it's not crucial to do so.) Spoon set Jell-O into hole, as much as it will hold, but not deeper than the cake itself. Top with other half of layer. (Again, a thin layer of frosting between layers will help hold it in place.) This is the spider body.

Take the small center piece you cut out and trim a small thin crescent shape out of one side, just enough to help it fit tightly against the other cake to form the spider's head.

Mix the food coloring with the frosting to turn it black. Frost cake completely. Create legs by inserting the licorice into the cake. Place gumballs on face to make eyes.

Store in refrigerator until ready to serve.

When the cake is cut, the Jell-O goo will spurt out.

Footsie Note: The original instructions for building the body didn't really work so I had to tweak them a bit. I also only used 4 pieces of licorice and cut them in half to form the legs. (I thought spiders had 8 legs, but if you want to give it 6 that's fine.) Since I didn't have any gumballs, I just used red decorating frosting for the eyes. I added the dots on top to make it resemble a black widow spider, but it should have been an hourglass shape instead.

I used black paste food coloring in hot fudge frosting. The darker the chocolate frosting is to start with, the easier it will be to turn it black.

You could also just use chocolate frosting and chocolate flavored licorice if you don't like black licorice.

* While the effect of the red or green Jell-O is probably better, I can't help thinking that pudding goes better with cake than Jell-O does. The next time I make this, I'm going to use pudding as the filling. Perhaps (depending on the flavors available) even those neon colored snack size puddings instead of instant or cooked pudding in a box. I've also discovered powdered food coloring which would probably be the best way to color pudding from a box, next to paste coloring, liquid food coloring might thin it out too much to set properly.