Elastocapillarity in insect adhesion: IRM investigation

The feet of many insects are covered with dense arrays of micrometric hair-like structures called setae. Liquid capillary bridges formed at the tip of these slender structures are responsible for the controlled adhesion of the insect on a large variety substrates. The resulting adhesion force is very efficient: it can exceed several times the body weight of the insect and yet vanish in a few milliseconds for fast detachment. The high aspect-ratio of setae suggests that flexibility is a key ingredient in this capillary-based adhesion mechanism. There is indeed a strong coupling between their elastic deformation and the shape of the liquid meniscus. In this experimental work, we observe and quantify the local deflection of dock beetle (Gastrophysa viridula) seta tips under perpendicular loading using interference reflection microscopy (IRM). Our results are then interpreted in the light of an analytic model of elastocapillarity through which we gain information about the optimal regime that these insects target