Use a pencil to trace around the rice cake on a piece of parchment paper.
Turn the paper over and pipe eight v-shaped legs around the perimeter of the rice cake.
Top with the rice cake.
Allow to set.
Pipe chocolate x's on the back of the candy eyes (or leave them as they are).
Remove the parchment paper from the rice cake, being careful not to pull off the spiders' legs (if this happens, use melted chocolate to 'glue' them back on).
Top with candy eyes.
Pipe a mouth with dark chocolate.
Insert two rod sprinkles for the fangs (or use flaked almonds).