The mechanical properties of the non-sticky spiral inNephilaorb webs (Araneae, Nephilidae)

Abstract

SUMMARYDetailed information on web geometry and the material properties of the various silks used enables the function of the webʼs different structures to be elucidated. In this study we investigated the non-sticky spiral in Nephila edulis webs, which in this species is not removed during web building. This permanent non-sticky spiral shows several modifications compared with others, e.g. temporary non-sticky spirals -it is zigzag shaped and wrapped around the radial thread at the elongated junctions. The material properties of the silk used in the non-sticky spiral and other scaffolding structures (i.e. radii, frame and anchor threads) were comparable. However, the fibre diameters differed, with the non-sticky spiral threads being significantly smaller. We used the measured data in a finite element (FE) model of the non-sticky spiral in a segment of the web. The FE analysis suggested that the observed zigzag index resulted from the application of very high pre-stresses to the outer turns of the non-sticky spiral. However, final pre-stress levels in the non-sticky spiral after reorganisation were down to 300MPa or 1.5-2 times the stress in the radii, which is probably closer to the stress applied by the spider during web building.

Tuning the instrument: sonic properties in the spider's web

“…Interface 13: 20160341 supercontraction in their webs could be controlled by actively altering radial thread tension during or after web building [18 -20], as well as co-spinning minor ampullate silk during web building. Minor ampullate silk is often co-spun with major ampullate and does not supercontract [44], but its biological role in webs is still unclear [54,55]. It could have a role in controlling the extent of supercontraction of major ampullate threads, as minor ampullate is often seen to be 10% longer than their co-spun counterparts, which suggests that 'supercontraction stress' can also create slack in minor ampullate threads [50].…”

Uncovering changes in spider orb-web topology owing to aerodynamic effects

“…Regarding the influence of permanent spiral threads, retained by Nephila spiders in their webs, their structural role has been recently studied by Hesselberg & Vollrath [40]. Considering exclusively aerodynamic aspects, it is reasonable to think that the presence of non-sticky spiral silk would not result in a higher drag because it is placed within gaps of the sticky spiral, replacing it rather than adding one.…”

Wet webs work better: Humidity, supercontraction and the performance of spider orb webs

“…Nephila webs also retain their auxiliary spiral, a temporary structure that is removed upon web completion in Argiope and likely functions to mechanically stabilize the closely packed capture spirals in Nephila webs (Foelix, 1987;Hesselberg and Vollrath, 2012;Kuntner et al, 2008). While it has sometimes been assumed that the temporary spiral is made of minor ampullate silk, evidence suggests it is actually made of MA silk (Hesselberg and Vollrath, 2012;Work, 1981b). Based on these differences, we expect Nephila webs to remain stiffer at high humidity compared with Argiope webs.…”

“…Furthermore, Nephila orb webs have ~50% more radii and their capture area is ~60% larger than Argiope webs (Sensenig et al, 2010) so that they likely deform less under the same impact energy (Fig.1). Nephila webs also retain their auxiliary spiral, a temporary structure that is removed upon web completion in Argiope and likely functions to mechanically stabilize the closely packed capture spirals in Nephila webs (Foelix, 1987;Hesselberg and Vollrath, 2012;Kuntner et al, 2008). While it has sometimes been assumed that the temporary spiral is made of minor ampullate silk, evidence suggests it is actually made of MA silk (Hesselberg and Vollrath, 2012;Work, 1981b).…”