Carding

Some spiders have a cribellum or sieve plate on top of the spinnerets, with which very thin spinning threads can be made. Because of the thinness of these threads (about 0.015 µm) the web looks blueish. These threads are being combed over the web, with use of the calamistrum. This is a kind of comb, located on the third or fourth pair of legs. This combing is called carding.