The influence of surface energy on the self-cleaning of insect adhesive devices

Abstract

SUMMARYThe ability of insects to adhere to surfaces is facilitated by the use of adhesive organs found on the terminal leg segments. These adhesive pads are inherently ʻtackyʼ and are expected to be subject to contamination by particulates, leading to loss of function. Here, we investigated the self-cleaning of ants and beetles by comparing the abilities of both hairy and smooth pad forms to selfclean on both high and low energy surfaces after being fouled with microspheres of two sizes and surface energies. We focused on the time taken to regain adhesive potential in unrestrained Hymenopterans (Polyrhachis dives and Myrmica scabrinodis) and Coccinellids (Harmonia axyridis and Adalia bipunctata) fouled with microspheres. We found that the reattainment of adhesion is influenced by particle type and size in Hymenopterans, with an interaction between the surface energy of the contaminating particle and substrate. In Coccinellids, reattainment of adhesion was only influenced by particle size and substrate properties. The adhesive organs of Coccinellids appear to possess superior self-cleaning abilities compared with those of Hymenopterans, although Hymenopterans exhibit better adhesion to both surface types.

Self-cleaning in tree frog toe pads; a mechanism for recovering from contamination without the need for grooming

“…Previous studies on geckos (Hansen and Autumn, 2005;Hu et al, 2012) and insects (Clemente et al, 2010;Orchard et al, 2012) have shown that self-cleaning occurs in both dry and wet adhesive pads. In the case of geckos, Hu and colleagues hypothesise that geckos clean their feet through a unique dynamic self-cleaning mechanism via digital hyperextension (Hu et al, 2012), though, as claimed by Hansen and Autumn, it is likely that particles are also shed because they have a greater attraction to the substrate than the animals' skin, which is ultrahydrophobic (Hansen and Autumn, 2005).…”

“…Edwards, 1982;Eigenbrode, 2004). Many organisms, such as insects, will typically clean by grooming (Orchard et al, 2012), and will do so when their adhesive pads prove ineffective regardless of contamination (Hosoda and Gorb, 2011). However, for many climbing animals, grooming is not a complete solution as the adhesive surface of a toe pad cannot be groomed when it is in use, providing adhesive and frictional forces to maintain the animal on, for instance, a vertical surface.…”

Effect of particulate contamination on adhesive ability and repellence in two species of ant (Hymenoptera; Formicidae)

“…As contamination and recovery time are strongly dependent upon contact area with the substrate, this continued presence of particles would slow the recovery process (Federle et al, 2002). This scrambling motion may work in a manner similar to that seen for hairy pads of insects (Clemente et al, 2010) and geckos (Hansen and Autumn, 2005); however, a detailed analysis of the mechanisms of the observed self-cleaning action in ants is beyond the scope of the current paper and is investigated in a separate publication (Orchard et al, 2012).…”

“…Workers of P. dives contaminated with high-energy particles regain adhesion after time spent scrambling at a high-energy smooth substrate in a shearing motion, similar to that seen in geckos and other insects in previous studies. This action may be a further example of 'self-cleaning' in smooth pads (Orchard et al, 2012).…”

“…Insects are able to reduce the detrimental effects of attachment pad contamination by using a number of different strategies that can be categorised under (1) passive 'self-cleaning' mechanisms, which have been found in insects with both smooth and hairy pad types (Clemente et al, 2010;Orchard et al, 2012), as well as geckos (Hansen and Autumn, 2005;Lee and Fearing, 2008); and (2) active grooming behaviours (see Hosoda and Gorb, 2011). In particular, Clemente et al have found that both smooth and hairy pads exhibit self-cleaning properties when contaminated with glass microspheres in a range of sizes (1-45m), finding that adhesion forces can return to normal after several steps (Clemente et al, 2010).…”