Scopulae, or scopula pads, are dense tufts of hair at the end of a spider's legs. They are found mostly on hunting spiders, for example

Salticidae Jumping spiders are a group of spiders that constitute the family (biology), family Salticidae. , this family contained over 600 species description, described genus, genera and over 6,000 described species, making it the largest family of spide ...

and Sparassidae. Scopulae consist of microscopic hairs, known as

seta In biology, setae (; seta ; ) are any of a number of different bristle- or hair-like structures on living organisms. Animal setae Protostomes Depending partly on their form and function, protostome setae may be called macrotrichia, chaetae, ...

e, which are each covered in even smaller hairs called setules or "end feet", resulting in a large contact area. When the scopulae are splayed out and placed against a surface, remarkable

adhesion Adhesion is the tendency of dissimilar particles or interface (matter), surfaces to cling to one another. (Cohesion (chemistry), Cohesion refers to the tendency of similar or identical particles and surfaces to cling to one another.) The ...

is produced due to the accumulation of adhesion of each individual setule interacting with a substrate. The adhesion may be due to the excretion of liquid from adhesive pads, although setae can adhere in both dry and wet modes. This enables

spider Spiders (order (biology), order Araneae) are air-breathing arthropods that have eight limbs, chelicerae with fangs generally able to inject venom, and spinnerets that extrude spider silk, silk. They are the largest order of arachnids and ran ...

s with scopulae to climb even sheer, smooth surfaces such as glass. The adhesion is so great that the spider could grip using this force and support 170 times its own weight. Possible physical mechanisms may include capillary, electrostatic, viscous, or

Van der Waals force In molecular physics and chemistry, the van der Waals force (sometimes van der Waals' force) is a distance-dependent interaction between atoms or molecules. Unlike ionic or covalent bonds, these attractions do not result from a chemical elec ...

. (Niederegger et al 2002; Betz and Kölsch, 2004) Scopulae have been used in taxonomy to identify families, especially

Mygalomorphae The Mygalomorphae, or mygalomorphs, are an infraorder of spiders, and comprise one of three major groups of living spiders with over 3,000 species, found on all continents except Antarctica. Many members are known as trapdoor spiders due to t ...

. Scopulae are found in addition to, not instead of, the claws at the end of each appendage, called tarsal claws.

References

{{Spider nav Spider anatomy