Step 1: Materials and Tools
Upholstery foam (I used 1" thick sheets)
Tape (any kind that will stick properly to the wire)
Glass pebbles (the kind usually used to fill decorative vases)
Scissors (or whatever tool you prefer to use to sculpt the foam)
Wire cutters, if your scissors aren't up to the task of cutting the wire
Hot glue gun
Paint brushes (both the normal kind and the foam kind)
Stir sticks (or something else you can use to mix paint)
Step 2: Wire Armature
Once you decide how your spider should look, start planning the size and how the armature should be shaped. You are more or less creating a skeleton for your spider and that skeleton will allow your spider to be posed. Obviously, you need to have your eight legs, but keep in mind that spiders have fangs too. If you want fangs that can be posed from a neutral position to attack mode, you'll need to plan for that at this stage so the prop will be solid when it is complete.
The drawing attached to this step shows basically how I set my spider's armature up.
Some things to note are that the legs are not eight pieces of wire, but four - each crosses over the wire for the body's armature and is taped in place so the legs won't end up falling off. The fangs are also one piece of wire bent in the middle to attach to the main body armature. Make sure you leave enough space for the legs around the wire. You don't want the legs to be overcrowded when you start building up the shape!
If your copper wire feels too flimsy, you can double it up and wrap two pieces together to make it stronger.
Step 3: The Body
The body will have two distinct parts. There's the carapace (the front end of the spider, where the legs attach) and the abdomen. In its most simplistic form, you can picture these parts as two balls glued together. You can deal with this two ways - carve the carapace and abdomen separately then glue them together, or you can do both out of one chunk of foam. For my spider, I did the former rather than the later.
To give your spider's body form, cut out a rectangle of 1" upholstery foam that is the right dimensions for the spider. This piece will be on the underside of your spider. Place it, making sure that the wire for the legs and fangs is properly spaced out. Cut another rectangle the same size and hot glue it on top of the first, sandwiching the wire between.
The key with hot glue is to work in small sections at a time, clamping the glued sections with your hands for a minute or two until it sets properly.
From there, glue additional layers of foam until you have a block big enough to carve the body shape you want out of. Using your scissors, cut away the unneeded foam until you get the shape you want. Be careful with the wire - it will move all over the place while you work and you don't want to poke yourself in the eye.
Step 4: The Legs and Fangs
As with the body, use scissors to carve away excess foam and shape the legs.
The same process goes for the fangs. You may want to cut the strips of foam longer than the wire for the fangs so that you can carve the foam to a point without the wire getting in the way.
For comparison, the photos in this step show the foam both before and after the carving.
Step 5: Painting the Legs (optional)
If you are making the legs contrast with the body, you will want to paint the legs. But paint alone won't work. It'll just seep into the foam and make it all crusty and decidedly unpleasant. The solution? Mix your paint with liquid latex! The latex won't seep in nearly as much and also provides a decent skin-like feel to the legs when it dries.
Fill a jar mostly with the liquid latex and drop a bit of the acrylic paint in. Mix it until the latex is a uniform colour. Don't add too much paint! The paint might seem watered down, but when the latex dries it will significantly darken whatever colour you mixed in. My latex was an elephant grey when I mixed it, but as you can see in the photo in the intro, it dried black.
Using your foam paint brushes, coat the legs and tip of the fangs with the liquid latex. Once it dries, go back and do another coat or two to smooth the surface. Just be sure that the latex over where your joints are going to be isn't overly thick. The thicker it is, the harder it will be to keep the legs posed.
Note: I didn't have as much latex as I would have liked when I did my spider, so the legs aren't as smooth as they could have been. If you want to have your spider's legs less rough than what you see in the intro photo, it's just a matter of more layers.
Step 6: Fur the Body
There's no real trick to this step. Just cut pieces of fur to fit your spider, sew them together and sew them over the spider's body. To deal with the legs and fangs, just sew a few stitches between the legs to keep the fur in place.
For the fangs, simply sew a fabric tube tapered to fit the shape of the bulky part of the fang. If you are opting for a fuzzy-legged spider, the same technique applies.
Step 7: The Eyes
I did mine using small glass pebbles. You can easily find them in craft stores. They're the ones that have a flat back and come in a variety of colours for use as decorative pot or vase filler. I used the clear ones.
To make the eyes, all I did was turn over the pebbles and paint the flat side. The first layer was the black dot for the pupil. After that dried, I painted the rest of the back with brown paint to fill in the rest of the eye. Once it dries, it's just a matter of hot gluing the eyes in place.
The number of eyes you use can vary. Some have six eyes, some have eight. The configuration of how they eyes are laid out is all over the place as well. My suggestion is to go with whatever you think looks good, even if it's not seen on a real spider.
Step 8: And You're Done!
In order to get my spider up the way you see it in the photo in the intro, I simply used fishing line. It's fairly strong and yet nearly invisible, especially after dark.