Air bubbles on the foot of the green dock beetle enhance foot grip by providing a dry area on underwater surfaces.

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Strongly adhesive oils secreted by microscopic hairs on the green dock beetle’s feet improve grip while the beetle is on land. However, these oils lose effectiveness when they are in contact with water. To compensate, the beetle traps air bubbles between these hairs to create a dry surface for the oils and hair to grip normally, enabling the beetle to walk or climb underwater.

This strategy was contributed by Rachel Major Edit Summary

References

“…our observations showed that these beetles may use air bubbles trapped between their adhesive setae to walk on flooded, inclined substrata or even under water. Beetle adhesion to hydrophilic surfaces under water was lower than that in air, whereas adhesion to hydrophobic surfaces under water was comparable to that in air. Oil-covered hairy pads had a pinning effect, retaining the air bubbles on their feet. Bubbles in contact with the hydrophobic substrate de-wetted the substrate and produced capillary adhesion. Additional capillary forces are generated by the pad's liquid bridges between the foot and the substrate.” (Hosodo et. al. 2012:4236)

"?When the structured polymer with the air bubble was pulled perpendicularly from the substrate in water, the force was rather strong. The air–solid interface on the substrate was affected by the hairy structure. When the shape of the air–solid interface on the substrate changed, the pull force also changed." (Hosodo et. al. 2012:4239)??

"A stable aqueous film (wetting film) is formed between the air bubble and the solid surface if the solid surface is hydrophilic… That is why, in the case of a hydrophobic surface, the aqueous film is not formed between the bubble and the solid surface. The bubble adheres directly to the hydrophobic surface. In beetles, the bubble makes direct contact of setae with the substrate surface possible… The force on the hydrophilic…surface under water might be additionally enhanced by the capillary bridges caused by an oily secretion on the setal tips of the de-wetted dry surface." (Hosodo et. al. 2012:4240-41)


Underwater locomotion in a terrestrial beetle: combination of surface de-wetting and capillary forces

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