Glue droplets on orb-weaver spider webs resist slippage through adhesion, elongation under load, and force transfer due to granules.

“Sticky viscous prey capture threads form the spiral elements of
spider orb-webs and are responsible for retaining insects that
strike a web. These threads are formed of regularly spaced aqueous
droplets that surround a pair of supporting axial fibers. When
a thread is flattened on a microscope slide a small, opaque granule
can usually be seen within each droplet. These granules have
been thought to be the glue that imparts thread adhesion.
Both independent contrast and standard regressions showed
that granule size is directly related to droplet volume and
indicated that granule volume is about 15% of droplet volume. We
attempted to find support for the hypothesized adhesive role of
granules by establishing an association between the contact surface
area and volume of these granules and the stickiness of the
viscous threads of 16 species in the context of a six-variable model
that describes thread stickiness. However, we found that granule
size made either an insignificant or a small negative contribution
to thread stickiness. Consequently, we hypothesize that
granules serve to anchor larger, surrounding layers of transparent
glycoprotein glue to the axial fibers of the thread, thereby
equipping droplets to resist slippage on the axial fibers as
these droplets generate adhesion, elongate under a load, and
transfer force to the axial fibers.” (Opell & Hendricks 2010:339)

Last Updated September 14, 2016