The influence of humidity on the attachment ability of the spiderPhilodromus dispar(Araneae, Philodromidae)

Abstract

Hairy attachment devices that are not supplemented with fluid secretion have evolved independently in lizards and spiders. van der Waals forces have previously been shown to be responsible for excellent adhesive properties of these structures, but it has recently been reported that wetting phenomena also play an important role in such 'dry adhesives'. To investigate the effect of ambient humidity on the attachment of the living spider Philodromus dispar, traction force was measured on a smooth epoxy resin surface at relative humidities (RHs) of 15, 50, 70, 80 and 99 per cent. The results show that attachment ability is significantly higher at an intermediate humidity compared with that in a dry atmosphere and at high humidity. Water condensation on the substrate surface almost completely abolishes adhesion. Experimental results obtained may be explained by an increase in capillarity or changes in mechanical properties of setae and spatulae owing to water absorption by the cuticle at an intermediate RH. The results obtained show dry adhesion limits under different environmental conditions and are important for understanding spider biology.

Influence of ambient humidity on the attachment ability of ladybird beetles (Coccinella septempunctata)

“…Temperature was continuously monitored in the chamber to ensure that the use of the heater did not lead to temperature increase within the chamber. For details, see [14]. …”

“…The traction force is dependent on the attachment ability of the pulling animal. This method has been used in previous studies [7,14,40]. We let the beetle pull for one minute and then repeated the experiment in a second run, to make sure that the performance of individual animals was stable.…”

“…Several studies showed that not only the intrinsic structure of an attachment organ determines its function, but also environmental parameters, such as the surface roughness or/and chemistry of the substrate [1,3–9]. Also the ambient temperature and humidity may affect the attachment ability of adhesive organs, as it was shown in the dry adhesive pads of geckoes [10–13] and spiders [14]. For small arthropods these conditions may highly vary micro-spatially, especially in the boundary layer of plant leaves [15].…”

Evaporation dynamics of tarsal liquid footprints in flies (Calliphora vicina)and beetles (Coccinella septempunctata)

“…In the dry attachment systems of geckos and spiders, humidity in the range of 60-80% has been found to be responsible for the observed increase in adhesion (Huber et al, 2005;Wolff and Gorb, 2011). Interestingly, the time spent in dry environments has only a negligible effect on the changes in attachment ability of the Colorado potato beetle over time .…”

Sticking to the story: outstanding challenges in gecko-inspired adhesives

“…Two prominent examples of other factors potentially contributing to gecko adhesion include contact electrification (Izadi et al, 2014) and capillary forces (Huber et al, 2005;Sun et al, 2005;Bhushan, 2007;Kim and Bhushan, 2008;Puthoff et al, 2010;Wolff and Gorb, 2012). Contact electrification is a phenomenon in which electric charges move between surfaces that come into contact with each other, such that one surface forms a net negative and the other a net positive charge.…”