Why are they called cobwebs?

I was taking photos of the mist on the canal early this morning when I spotted this web. Then I spotted another one, and another and another .... 

I suppose they must always be there but we don't normally notice them until they are covered in water droplets.

Thank you all very much for yesterdays hearts and stars, I was not expecting that for my humble hoverfly.  You are all very nice people :-)