In spiders, the calamistrum is a row of specialized leg bristles used to comb out fine bands of silk. It is only found on cribellate spiders, that is, spiders that possess the spinning organ known as the cribellum. The calamistrum and cribellum are used to form the hackled bands of silk which are characteristic of the webs of these spiders. The calamistrum is found on the upper margin of the metatarsus of the hind legs. Each bristle of the calamistrum is serrated on one side and smooth on the other.