Put real spiderwebs on paper. preserve a spiderweb on paper to explore/look at. or put the black paper behind it so it can be seen in detail and then take a picture so you don't have to destroy the spider's web.
A nice little roundup of fun crafts for kids to make that parents will actually enjoy doing, too! A lot of these crafts and activities are for kids of all ages, but most of them are probably more appropriate for ages