The grand design: Form and colour in animalsJanuary 1, 1970
“Thus, in an aerial system, water can act as an adequate glue by a mechanism commonly referred to as ‘capillary adhesion.’ Aphids appear to use it to adhere to surfaces (Dixon, Croghan, and Gowing 1990). And it almost certainly helps a tree frog rest placidly on a vertical pane of glass.” (Vogel 2003:428)
Comparative Biomechanics: Life's Physical WorldPrinceton University PressJanuary 1, 2003
“1. The adhesive force acting between the adhesive organs and substratum for a number of aphid species has been studied. In the case of Aphis fabae, the force per foot is about 10 µN. This is much the same on both glass (amphiphilic) and silanized glass (hydrophobic) surfaces. The adhesive force is about 20 times greater than the gravitational force tending to detach each foot of an inverted aphid.
“2. The mechanism of adhesion was considered. Direct van der Waals forces and viscous force were shown to be trivial and electrostatic force and muscularforce were shown to be improbable. An adhesive force resulting from surface tension at an air-fluid interface was shown to be adequate and likely.
“3. Evidence was collected that the working fluid of the adhesive organ has the properties of a dilute aqueous solution of a surfactant. There is a considerable reserve of fluid, presumably in the cuticle of the adhesive organ.” (Dixon et al. 1990:243)