Tribology of a snail (terrestrial gastropod)

Abstract

The locomotion characteristics of a snail (terrestrial gastropod) that can move forward extremely smoothly not only on the horizontal substratum but also even on walls and reverse on ceilings, are examined experimentally in the tribological standpoint. The locomotion can be achieved by the combination of the progressive wave (pedal wave) of the ventral surface of the foot and the secreted viscous mucus. From pulling off force experiments, the holding force of a snail to a substratum does not depend on the sole area. According to NMR analysis, viscous secreted mucus of consists of about 93% of water and 7% of glycoprotein. From the experimental examinations of mechanical properties such as viscosity variation versus shear rate, the relationship between shear strength and mucus film thickness and the relationship between shear rate and shear stress, the secreted viscous mucus of a snail is a non-Newtonian fluid that has visco-plastic characteristics. The movement of snails is obtained by a fine peristalitic motion, based on the combination of the concave shaped contraction of the ventral surface muscle during the passage of the pedal wave and the stretched ventral surface muscle without pedal wave passing. The driving force is generated at the anterior part of the ventral surface as a whole and the posterior part is only dragged. The ventral surface of the foot has a sucking in function and snails circulate secreted mucus around the sole and reuse it skillfully.