I bought two pairs of cheap black pantyhose, cut off the legs, and stuffed them with old plastic grocery bags that I'd been saving up for this Homemade Spider Costume. The effect was very bumpy, but I liked it.
I took a black long-sleeved shirt, and sewed the legs of the pantyhose to the sides. After that, I tightly tied off each leg into four different segments with string, measuring with a ruler to make sure that the legs were uniformly segmented.
I tied about a foot of string between the place where I tied off the outermost sections of the legs, so that the top and the bottom leg were linked. After that, I tied one end of another piece of string the same size to EACH of the top legs, and then tied each of the other ends to hair elastics, so that I wear the hair elastics on my wrists, and move the legs uniformly, but also release the legs if I needed to use my hands/arms properly. I had to try the shirt part of the costume on a few times, to make sure I'd cut the strings to a manageable length, so the legs wouldn't drag on the ground, etc.
I took the "panty" part of BOTH pairs of pantyhose, turned it inside out, and sewed the holes shut (where I cut off the legs). I then cut large circles out of a scrap of white T-shirt fabric, put a bunch of smaller scraps in the middle of each circle, brought the edges in, and sewed them shut to make eyeballs (if I had it to do again, I'd use something that's more "perfectly round" like Ping-Pong balls, but anyway. After that, I drew a small black circle with a Sharpie in the middle of each rough white "ball" on the smooth side, and then I painted over the circles with black nail polish, to make sure they were vivid enough/didn't run. I then sewed the finished eyeballs to the front of one of the "pantyhose caps" I'd created.
I put on a pair of black yoga pants, the "spider shirt" I'd created, and then layered the "pantyhose cap" with eyeballs over the one without (I used cheap pantyhose that were pretty thin and see-through). After that, I put the hair elastics on my wrists, so I could manipulate my spider legs.
That flashing thing in my hand is a light-up spider wand I found at a discount store. One eye flashes red, and the other green, and the spider is sitting in the middle of a web made of white pipe cleaners. Completely optional, but still cool.
GLITCHES: 1. Since I used cheap pantyhose, my spider legs got a few runs in them, so I'd suggest using thicker hose, if possible. 2. My leg strings also broke at least once, so I'd use fishing line if you have some. 3. Like I said about the eyes--it might be advisable to use something more "round." You don't even have to buy anything special--even just cutting the toes off of two different white socks (or red, yellow, orange, or fluorescent green socks) would work.