The Halloween experts at DIY Network have instructions on how to make a spider costume.
Rubies Costume Co Pet Spider Harness, Medium
Thinking about a Halloween Spider Costume? Check out the Hairy Tarantula Halloween Costume: uses foam for shape so this spider costume is flexible and comfortable.
If you're going for something creepy AND silly, this Halloween hairstyles spider hair bun by SweetHearts Hair Design is just what you're looking for.