Skin of earthworms repels soil adhesion with a thin water film, created by electro-osmotic flow.

Earthworms use self-generated electricity to aggregate minute quantities of water dispersed throughout soil, reducing their drag without toxic lubricants or external energy. At rest, the difference in electric potential between an earthworm’s surface and its environment is essentially zero, but the moment it starts to move, a negative electrical charge forms wherever its body is in motion, attracting positively-charged water molecules out of surrounding soil precisely where friction with the soil is greatest. This auto-lubrication results from small amounts of cutaneous bioelectrical current (e.g., 40 millivolts) extracting locally available water supplies from the interstitial spaces of the soil. Scale-up tests applying 12 volts of electrical current to bulldozer blades have demonstrated soil resistance reductions of up to 32% over conventional blades, representing dramatic potential energy savings, for instance, in site preparation activities.


“When a soil animal is in contact with soil, a microscopic Electro-osmotic system is formed between the stimulated body parts and the other parts nearby. As a result, water in the adjacent soil moves to the contact zones by the action of potential difference, the water film at the contact interfaces become thicker, so that the soil adhesion to the body surfaces would be reduced through lubrication. Although the amplitude of the action potential of soil animals is small, a microscopic Electro-osmostic system can be formed because the distance between the positive pole and the negative pole is very short. The zone of negative polarity produced by stimulation from the contacting soil is on the same surface as the resting body part near to stimulating zone.” (Collins 2004:220)

Design and Nature II: Comparing Design in Nature With Science and Engineering (Design and Nature) (Design and Nature, 6)September 6, 2004
M. W. Collins