Use a lollipop stick (or something with a similar shape) to poke 4 holes in either side of each brownie.

Combine powdered sugar and water to create a thick icing that can be used "glue". A little bit of water goes a long way so add only a very small drop, stir, and only add more if necessary.

When you have the proper consistency, add a dab of the icing to the back of each candy eyeball, then stick them on the brownies.

Lastly, dip the end of each "leg" in the icing, then into a hole in the brownie. Repeat until all the "spiders" have 8 legs.