Cut twenty-four 7cm-long, thin strips from licorice. Using damp hands, shape 1 tablespoon of crackle mixture into a 5cm round. Lay 4 licorice strips across round, overhanging evenly on each side. Sandwich with another round of crackle mixture. Use icing to secure M&Ms as eyes. Place on prepared tray. Repeat with remaining crackle mixture, licorice strips, icing and M&Ms to make 5 more spiders.