Preheat the oven to 375 degrees F and line a baking sheet with parchment paper.
Cut the mozzarella into 8 sticks, about 2 inches long, for the spider bodies.
Separate the crescent dough into its 8 triangles (or pinch the seams and cut into 8 strips).
Wrap a piece of dough around each stick of cheese so the cheese is covered, leaving a little dough extending past both ends.
Flatten the dough at each end, then use kitchen scissors to snip two slits into each flattened end, creating the spider legs.
Place the spiders on the baking sheet and brush each one with the beaten egg.
Bake for 12 -14 minutes, until the dough is golden.
While the spiders are still warm, attach two edible candy eyes to each one using a tiny dab of mustard to hold them in place. Serve with warm marinara sauce for dipping.