Comparative study of the fluid viscosity in tarsal hairy attachment systems of flies and beetles

Abstract

Wet adhesive systems of insects strongly rely for their function on the formation of capillary bridges with the substrate. Studies on the chemical composition and evaporation dynamics of tarsal secretions strongly suggest a difference in chemistry of secretion in beetles and flies, both possessing hairy attachment devices. This difference is assumed to influence the viscosity of the secretion. Here, we applied a microrheological technique, based on the immersion of nanometric beads in the collected tarsal footprints, to estimate secretion viscosity in a beetle (Coccinella septempunctata) and a fly (Calliphora vicina). Both species studied possess distinct differences in viscosity, the median of which was calculated as 21.8 and 10.9 mPa s, respectively. We further present an approximate theoretical model to calculate the contact formation time of spatula-like terminal contact elements using the viscosity data of the covering fluid.

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

“…Due to its polarity it can work as a bonding agent between two surfaces, and therefore have a substantial effect on adhesion [18–21]. In insects the terminal contact elements of tenent setae are not dry, but rather wetted by a fluid secretion that is usually a micro-emulsion of water and oil, with varying fractions of substances [22–31]. The mixture of both polar and non-polar substances presumably helps to wet both hydrophobic and hydrophilic surfaces building a fluid meniscus between the seta and the substrate to yield high capillary forces (wet adhesion).…”

“…The mixture of both polar and non-polar substances presumably helps to wet both hydrophobic and hydrophilic surfaces building a fluid meniscus between the seta and the substrate to yield high capillary forces (wet adhesion). The fluid can increase the contact area by filling minute cavities of micro- and nano-rough surfaces, where setae otherwise cannot adapt to, and prevents slipping of the foot due to its specific rheological properties [31–35]. It was demonstrated that the presence of these secretions is crucial for the function of insect adhesive organs [6,36].…”

It's Not a Bug, It's a Feature: Functional Materials in Insects

“…This finding provides insight into the role that viscous forces play in general insect adhesion: fly secretions are suited for shorter detachment times to escape from predators, while beetles sacrifice rapid mobility for increased adhesive force. [65] …”

“…In a comparative study of adhesive secretion viscosities, Peisker et al found that fly secretions (from Calliphora vicinia) have a much lower viscosity (10.9 mPa s) than secretions from beetles (Coccinella septempunctata, 21.8 mPa s). [65] Both of these insects have fibrous adhesive feet, so the difference can be attributed to the composition of the fluid. This finding provides insight into the role that viscous forces play in general insect adhesion: fly secretions are suited for shorter detachment times to escape from predators, while beetles sacrifice rapid mobility for increased adhesive force.…”

“…Chemoreceptive sensilla Gypsy moths, [433][434][435] nun moths, [433] silk moths, [629] tobacco hawk moths [440,441] Collective materials Building and fungus cultivation Termites [630] Built structures Honeybees [2] Group thermoregulation Termites, [528] bees, [512,563] wasps [512,563] Wind harvesting Termites [511,631] Locomotion Locomotive appendages Jumping insects, [128] locust, [632,633] cicadas [634] Emulsions and biphasic solutions Adhesion Permanent adhesives Flies, [635,636] praying mantis, [68] asparagus beetle, [637] gum moths [57] Temporary adhesives Locusts, [58] grasshoppers, [59] flies, [65] beetles [65] Chemical sensing and defense…”