Surface roughness effects on attachment ability of the spider Philodromus dispar (Araneae, Philodromidae)

Abstract

SUMMARYThe morphology of the tarsal attachment system of the running spider Philodromus dispar Walckenaer 1826 (Araneae, Philodomidae) was studied using scanning electron microscopy and its performance was experimentally tested in traction force measurements. Each pretarsus bears a hierarchically built hairy adhesive pad that consists of a dense array of flattened setae covered with numerous microtrichia on the substrate-facing side. Microtrichia carry spatulate end tips that allow close contact with the substrate. Forces were estimated on tethered living specimens on rough epoxy resin surfaces (asperity size 0.3, 1, 3, 9 and 12m) and on a smooth surface as a control. A strong reduction in adhesion was observed for substrates with an asperity size of 0.3 and 1m. Comparison of the present data with previous results of different organisms demonstrates that the difference in force reduction on rough substrata depends on the dimensions of terminal contact elements (spatulae).

Functional morphology of tarsal adhesive pads and attachment ability in ticksIxodes ricinus(Arachnida, Acari, Ixodidae)

“…Although we just evaluated the proportion of animals that remained attached after substrate inversion and did not measure forces during inversion, our observations roughly correspond to previous reports, where roughness values of 0.3, 1.0 and 3.0 µm have been stated to decrease friction forces in insect and spider attachment pads Voigt et al, 2008;Al Bitar et al, 2010;Wolff and Gorb, 2012). This effect is thought to be due to the decrease of contact area between adhesive pads and substrates and to the failure of claw interlocking.…”

Effect of surface roughness on attachment ability of locust Locusta migratoria manilensis

“…Similar phenomena have previously been demonstrated in other insects and animals with hairy-structured pad, as spider P. dispar on substrates with surface asperities of 0.3 and 1.0 mm [15], and beetle G. virigula on surface with root mean square roughness of 0.1 mm or substrate with asperity size of 0.05 mm [13,31], and gecko G. gecko on substrates with root mean square roughness ranging from 0.1 to 0.3 mm [14,32,33]. All these studies confirmed the existence of critical surface roughness which could result in a remarkable decrease of insect's attachment ability, and this significant reduction results from the surface asperities of these substrates can prohibit the hairy-structured pad from acquiring adequate contact area.…”

“…1a). Referring to a similar method previously described [15,[20][21][22][23], the locust was connected to the force sensor (along the load direction) utilizing a thin thread (length approx. 15 cm) fastened its neck position, and then put on the selected substrate (Fig.…”

“…2 When the substrate bears roughness R a values more than 5.103 mm, the corresponding peak-valley distance is about higher than 25.181 mm (value derived from roughmeter TR200, sample length 2.5 mm). For most insects with hairy-structured pad, attributing to the rather small dimension of terminal attachment element (spatula size of single setae in spider 0.9 mm, flies 1-2 mm, beetle 7 mm), these substrates are similar to complanate surfaces and still permit adequate duplication [12,15]. Since the locust pad possesses an overall structure (Fig.…”

“…Behavior observation and force measurement demonstrated that substrates with asperity dimension ranging from 0.3 to 1.0 mm significantly reduce the locomotion ability of fly Musca domestica [12], beetle Gastrophysa viridula [13], lizard Gekko gecko [14], and spider Philodromus dispar [15]. Explanation has been put forward to describe the interaction between rigid claw and substrate, presenting that insect depends upon mechanical interlock to guarantee effective locomotion and quiescence when surface roughness is much greater than the claw tip diameter, but when surface roughness is comparable to or smaller than the claw tip diameter, no effective mechanical interlock can be generated, therefore the attachment ability is drastically reduced [16].…”