the fluid excreted by the silk glands of certain arthropods (Arachneidae, Tetranychoidea, Pseudoscorpionidea, Embioptera), which may be drawn in the form of fine threads that rapidly harden in the air. Spider silk, which is similar to the silk of silkworms, consists mainly of very sturdy fibroin that is insoluble in water. The silk is not only resilient and strong but also sticky. It is used by the animal to construct snares, shelters, and egg cocoons.