Arthropod adhesion
[3] Additionally, tree frogs and some mammals such as the arboreal possum and bats also make use of smooth adhesive pads.
[1][2] The use of adhesive pads for locomotion across non-horizontal surfaces is a trait that evolved separately in different species, making it an example of convergent evolution.
[2] The exact mechanisms of arthropod adhesion are still unknown for some species, but this topic is of great importance to biologists, physicists, and engineers.
[6] Since these effects are based on fundamental physical principles and highly related to the shape of the structure, they are also the same for artificial surfaces with similar geometry.
[5] Adhesive chemical secretions are also used for predation defence, mating, holding substrates, anchor eggs, building retreats, prey capture, and self-grooming.
[4] Smooth adhesion has evolved in many families of organisms independently, which creates structures that appear unrelated to each other but generate the same function.
[1] There are different types of smooth adhesive pads in these organisms such as the arolia, pulvilli, and euplantulae, all of which have a cuticle that is extremely soft and deformable.
[2] Some functional principles of smooth pads (adaptability, viscoelasticity, pressure sensitivity) are similar to those known from industrial pressure-sensitive adhesion.
[3] The internal fibrous structure of smooth pads might be vital to their ability to deform, for shear-induced lateral increase in contact area, or for efficient transfer of tensile forces, yet at this point its specific function is unknown.
[4] Hairy attachment pads employed few other features, such as flaw tolerance, lower sensitivity to contamination, and roughness.
[6] Hairy attachment systems are typical for evolutionary younger and successful insect groups, such as Coleoptera and Diptera.
[6] The acanthae are hollow inside, and some have pores under the terminal plate, which presumably deliver an adhesive secretion directly to the contact area.
[6] Hairy attachment pads of reduviid bugs,[8] flies [9] and beetles[10] secrete fluid into the contact area.
[6] At low humidity, adhesion strongly depends on the amount of liquid deposited on the surface, and therefore contact duration.
[12] Adhesive foot pads only stick when pulled toward the body, but unstick when moved away from it, which allows for effortless and rapid detachment.
(Bullock, Drechsler, & Federle, 2008) Adhesive chemical secretions are also used for predation defence, mating, holding substrates, anchoring eggs, building retreats, prey capture, and self grooming.
Structures for use in repelling attackers or temporarily or permanently adhering to a substratum or a mating partner have been found in the developmental stages of the egg, larvae, pupae, and adult.
[4] Epidermal glands and their secretions are highly diverse and vary in their function for: protection from adverse environmental conditions and microbial contamination, regulation of water balance, communication with pheromones and alelochemicals, defense from predators and parasites, construction and making food accessible.
[4] Natural adhesives used by both plants and animals are composed of only a few basic components, such as proteins, polysaccharides, polyphenols, and lipids that are mixed in various combinations.
[4] Adhesives that are for mechanical work are often composed of high-molecular compounds containing proteins, resins, mixtures of long-chain hydrocarbons and mucopolysaccharides, or waxes.
[4] Defensive adhesive secretions often combine their mechanical effect with a low molecular weight chemical irritant to deter predators.
[3] Smooth adhesive pads are an example of convergent evolution between amphibians (geckos and frogs), arthropods, and mammals (possum).
[7] Hairy attachment systems of the gekkonid lizards and spiders do not produce fluids; these organisms rely on van der Waals interactions for the generation of strong attractive forces.
[4][6] Additionally, some research indicates that the wrinkling effect that occurs in human fingers when submerged in water acts to increase grip on wet objects.
