Sticky Feet -- Evidence for Self-Cleaning Adhesive Pads of Insects


Have you ever noticed that insects' feet just never seem to get dirty? No matter that they've been standing on, they still stick to the next surface. The same can't be said for man-made adhesives: sticky tape soon becomes contaminated and fails to bond. And many insects maintain the same adhesive structures throughout the whole of their adult lives, so they have to keep them clean somehow.
 ‘Broadly speaking insects use two adhesive systems: smooth and hairy,’ explains Bullock. Some insects' feet are smooth and covered in a thin fluid film that helps them to hold on tight, while other insects' feet are coated with fluid covered microscopic hairs that mould to surfaces as they attach. Knowing that stick insects have smooth feet while dock beetles have hairy feet, the team decided to find out whether both species could clean their dirty feet by walking across a smooth surface.

Insect Biomechanics Workgroup

Welcome to the Insect Biomechanics Workgroup Cambridge!

We are interested in the functional morphology and comparative biomechanics of insects with a special focus on the mechanisms of surface adhesion and insect-plant interactions.

Design and function of adhesive systems

Animal adhesive organs have come into the focus of scientific attention over the last decade because it is hoped that some of their most interesting properties can be mimicked to make novel, superior adhesives. Although attempts to fabricate "biomimetic" adhesives are meanwhile flourishing worldwide, it is striking that the basic function of many animal "model" adhesives is still not well understood. Animal adhesives can not only stick very well to diverse surfaces, but they are also self-cleaning and rapidly controllable, i.e. they can detach very easily if necessary. How they achieve this impressive performance is not yet entirely clear.

Journal of Experimental Biology 213, 635-642 (2010)

Evidence for self-cleaning in fluid-based smooth and hairy adhesive systems of insects

Christofer J. Clemente, James M. R. Bullock, Andrew Beale and Walter Federle

(A) Experimental setup for recording friction, adhesion and contact area of insect adhesive pads. Contact area images show hairy pad (above) and smooth pad (below). (B) Order and pattern of ‘steps’ performed on the glass plate to test the effect of contamination and self-cleaning. Four initial steps were followed by a ‘contamination step’ and eight steps on clean areas of the glass plate.

 Scanning electron microscopy images of adhesive pads of G. viridula after contamination with beads of different sizes, followed by eight consecutive steps to allow self-cleaning. (A,B) 1 µm-diameter beads; (C,D) 10 µm-diameter beads; (E,F) 45 µm-diameter beads. As pads contaminated with 45 µm beads did not contain any beads after self-cleaning, E and F show a freshly contaminated pad.

Self-cleaning ability is an important property of biological adhesive systems and will be an important criterion for the design of bio-inspired adhesives. Scotch tape is a prime example of an adhesive that is not self-cleaning and consequently it is of no use after several applications. Efforts are underway to manufacture a fibrillar adhesive that is effective after more than one use