Cribellum

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Cribellum literally means "little sieve", and in biology the term generally applies to anatomical structures in the form of tiny perforated plates.

In certain groups of diatoms it refers to microscopically punctured regions of the frustule, or outer layer.

In certain groups of spider species, so-called cribellate spiders, the cribellum is a silk spinning organ. Unlike the usual spinnerets of spiders, the cribellum consists of one or more plates covered in thousands of tiny spigots, tiny holes that hardly project from the surface, in contrast to the elongated spigots that project from spinnerets.^[1] These minute spigots produce extremely fine fibers, merely tens of nanometres thick, which are combed out by the spider's calamistrum, producing silk with a woolly texture.

The fibers are so small in diameter that they are strongly subject to Van der Waals forces.^[2] In addition, the fibres have a surface that absorbs waxes from the epicuticle of insect prey on contact. This creates a powerful adhesion without any liquid glue that tends to dry out.^[3]

The spider cribellum is a functional homolog of the anterior median spinnerets of Mesothelae and Mygalomorphae, which do not have a cribellum.