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

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"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 glycoprotein 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)

Journal article
The role of granules within viscous capture threads of orb-weaving spidersJournal of Experimental BiologyDecember 28, 2009
B. D. Opell, M. L. Hendricks

Journal article
Adhesive recruitment by the viscous capture threads of araneoid orb-weaving spidersJournal of Experimental BiologyFebruary 3, 2007
B. D. Opell, M. L. Hendricks

Journal article
Humidity affects the extensibility of an orb-weaving spider's viscous thread dropletsJournal of Experimental BiologyAugust 10, 2011
B. D. Opell, S. E. Karinshak, M. A. Sigler

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Living System/s

Orb WeaversAraneidaeFamily

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