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.
Nature Mandala ~ Take your storytime kids on a nature walk and build a collage out of what you find! Maybe try this as an excursion. Or collect heaps of things from nature, hide them around the room and go on a treasure hunt