Paint the polystyrene semi-circles black with several coats of paint and leave to dry – you will need one for each spider you want to make.
On the flat side of the polystyrene glue four matching pipe cleaners onto the bottom of the spider, crossing them over in the centre. Repeat for all spiders, using a different colour for each one so you can tell them apart. Leave to dry.
Bend the pipe cleaners on the bottom into spider leg shapes. Cut a smile from orange craft foam and stick onto the top of each spider along with a pair of googly eyes.
Making the web is like making a giant snowflake! Cut the top, bottom and sides off a bin bag so you have two square sheets. Put one sheet aside.
Fold your square in half diagonally to form a triangle. Fold again and then again to form a smaller triangle.
Starting at the bottom, cut the sides away keeping a thick line down the middle, as you would a paper snowflake. Continue all the way down the bin bag
Open the bin bag out to reveal a spider web!