The whole is more than the sum of all its parts: collective effect of spider attachment organs

Abstract

Dynamic attachment is the key to moving safely and fast in a threedimensional environment. Among lizards, hexapods and arachnids, several lineages have evolved hairy foot pads that can generate strong friction and adhesion on both smooth and rough surfaces. A strongly expressed directionality of attachment structures results in an anisotropy of frictional properties, which might be crucial for attachment control. In a natural situation, more than one leg is usually in contact with the substrate. In order to understand the collective effect of hairy foot pads in the hunting spider Cupiennius salei (Arachnida, Ctenidae), we performed vertical pulling experiments combined with stepwise disabling of the pads. We found the attachment force of the spider to be not simply the sum of single leg forces because with leg pair deactivation a much greater decrease in attachment forces was found than was predicted by just the loss of available adhesive pad area. This indicates that overall adhesion ability of the spider is strongly dependent on the antagonistic work of opposing legs, and the apparent contact area plays only a minor role. It is concluded that the coordinated action of the legs is crucial for adhesion control and for fast and easy detachment. The cumulative effect of anisotropic fibrillar adhesive structures could be potentially interesting for biomimetic applications, such as novel gripping devices.

Locomotion and attachment of leaf beetle larvaeGastrophysa viridula(Coleoptera, Chrysomelidae)

“…Although the contact area of the pygopod is larger than the summed contact areas of the tarsal pads, the distribution of all synergistically acting seven contact points around the larva's body might be of greater importance for keeping attachment stability and for preventing peeling off, as likewise suggested for caterpillars [30]. Similar results were recently described in spiders, where the collective effect of several legs during simultaneous attachment was stronger than the mathematical sum of adhesive forces generated by individual legs [56]. In centrifugation tests, larvae could withstand greater centrifugal forces on the horizontal than on the vertical Plexiglas drum surface, consistent with experiments performed with other insect species [57].…”

Composition and substrate-dependent strength of the silken attachment discs in spiders

“…In contrast to the experimental data provided by Sahni et al [13], the multiple peeling theory by Pugno et al [12] predicts that such dendritic architecture must be the optimal one for strong attachment at low material cost. The latter paper is based on the so-called theory of multiple peeling suggesting that a simultaneous detachment of opposing adhesive tapes leads to much higher adhesion than the sum of detachment forces needed to peel-off each tape separately [35], a model that is highly applicable to biological locomotory attachment systems, such as gecko feet or arthropod adhesive foot pads [36]. The previous models of the 'staple-pin' architecture [12,13] presume that initially the dragline is directly cemented to the substrate by means of the pyriform threads.…”

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

“…This capability is sufficient for initial attachment of the forelegs to vertebrate hosts during transition from banker plants. However, one has to keep in mind that a single leg in contact commonly generates a lower force when compared with the contribution of legs acting together in concert with each other (Wohlfart et al, 2014).…”