What structures on a spider's abdomen produce silk?

What structures on a spider's abdomen produce silk? Spinnerets. These movable organs sit on the underside or rear of the abdomen, also called the opisthosoma, and release silk through microscopic openings called spigots.

Most spiders have three pairs of spinnerets, though some species have two, four, or eight. Each spinneret connects to several silk glands, allowing a spider to produce different fibers for draglines, web frames, sticky capture threads, egg sacs, prey-wrapping, and shelter. Silk begins as a concentrated protein solution and becomes a strong fiber as it is drawn through the spinning apparatus.

Spinnerets are often confused with pedipalps, tarsi, or chelicerae. Pedipalps are the small appendages near the mouth, tarsi are the final segments of the legs, and chelicerae bear the fangs. None of these are the standard silk-producing structures. Not every spider builds a prey-catching web, but even hunting spiders commonly use spinneret-produced silk as a safety line or retreat.

The spinneret's many spigots also help explain why spider silk comes in several forms. A single spider can combine fibers with different thicknesses and properties, making the spinneret a remarkably precise biological spinning system.