1 Pkg. of styrofoam balls
1 can gold metallic spray paint
The first step is to cut off about 1/3 of the ball to create a flat bottom surface. You can use a serrated knife to accomplish this. I started at the center of the ball in placing the skewers. I cut off about 2/3 of the skewers for the center so the "spines" started small and grew longer as they continued out to the perimeter of the ball.
It was really just a matter of eyeballing it as I continued adding skewers. Once you like the amount you have, head outside to paint them gold. I added a couple of coats, front and back. Letting it dry in between coats.
Finally to attach them to the wall, simply place a nail in the wall and push on the front of the urchin so the nail penetrates the styrofoam ball.
I know you've also seen table versions of these.....those would also be easy enough to make by leaving the ball whole and adding skewers all the way around the ball. Have Fun!