So I put the ideas down on paper and after some tweaking (and lots of cajoling) here's how the big, bad but awfully cute spider-boy came to be:
The spider legs were made with black socks stuffed with newspaper and plastic groceries bags. A chopstick tightly taped to a strip of cardboard and inserted into each of the socks kept them from bending.
The legs were then secured on a hard cardboard base with hockey-clear tape and hockey-stick tape: the cardboard base was light but sturdy; the clear tape would not ruin the socks just in case I want to reuse them for another project; hockey-stick tapes are stretchable and very strong, good enough to hold everything together!
The spider body was simply a black garbage bag (just the bottom portion only) that was shaped into an oblong shape with bunched up newspapers and covered with a piece of black fuzzy fabric.
The body and legs were attached to my son's back (very much like a backpack) using shoulder straps fashioned out of large black elastics and green fasteners from an old Old Navy lunch box.
I decided to try face painting but had the feeling that my 7-year-old boy was not the best candidate to let me experiment on him (not a surprise, right?). So I used Autodesk Sketchbook Mobile Express and sketched out a few different designs a couple of days before Halloween. My son liked the sample sketches so much that he decided it was definitely worth sitting still - all of the 15 minutes it took me to apply the makeup.
We were quite happy with the results and needless to say, the costume was a big hit at school! The 'legged-backpack' was a perfect fit over a long sleeve black shirt and jacket, the makeup was dramatic and great theater as it was really spooky looking in the dark Halloween night, and my son was channeling his fellow Arachnids with glee. And no. No brown paper bag for me. But I did bug my son a million times - "You DID say that your mom made it, right? right?".