Feet Prevent Slipping

macro focus of an insect with large green eyes and micro bristles on its legs stands on a white surface

Biological Strategy

Steam fly

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Attach Temporarily

Living systems must sometimes, temporarily, stay in one place, climb or otherwise move around, or hold things together. This entails attaching temporarily with the ability to release, which minimizes energy and material use. Some living systems repeatedly attach, detach, and reattach for an extended time, such as over their lifetimes. Despite being temporary, these attachments must withstand physical and other forces until they have achieved their purpose. Therefore, living systems have adapted attachment mechanisms optimized for the amount of time or number of times they must be used. An example is the gecko, which climbs walls by attaching its toes for less than a second. Other examples include insects that attach their eggs to a leaf until they hatch, and insects whose wings temporarily attach during flight but separate after landing.

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Insects

Class Insecta (“an insect”): Flies, ants, beetles, cockroaches, fleas, dragonflies

Insects are the most abundant arthropods—they make up 90% of the animals in the phylum. They’re found everywhere on earth except the deep ocean, and scientists estimate there are millions of insects not yet described. Most live on land, but many live in freshwater or saltwater marshes for part of their life cycles. Insects have three distinct body sections: a head, which has specialized mouthparts, a thorax, which has jointed legs, and an abdomen. They have well-developed nervous and sensory systems, and are the only invertebrate that can fly, thanks to their lightweight exoskeletons and small size.

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Feet of insects stick to surfaces using nanometer-thin films of liquid secretions.

“Many insects cling to vertical and inverted surfaces with pads that
adhere by nanometre-thin films of liquid secretion. This fluid is an
emulsion, consisting of watery droplets in an oily continuous phase.
The detailed function of its two-phasic nature has remained unclear.
Here we show that the pad emulsion provides a mechanism that prevents
insects from slipping on smooth substrates. We discovered that it is
possible to manipulate the adhesive secretion in vivo
using smooth polyimide substrates that selectively absorb its watery
component. While thick layers of polyimide spin-coated onto glass
removed all visible hydrophilic droplets, thin coatings left the
emulsion in its typical form. Force measurements of stick insect pads
sliding on these substrates demonstrated that the reduction of the
watery phase resulted in a significant decrease in friction forces.
Artificial control pads made of polydimethylsiloxane showed no
difference when tested on the same substrates, confirming that the
effect is caused by the insects’ fluid-based adhesive system. Our
findings suggest that insect adhesive pads use emulsions with
non-Newtonian properties, which may have been optimized by natural
selection. Emulsions as adhesive secretions combine the benefits of
‘wet’ adhesion and resistance against shear forces.” (Dirks et al. 2009)

Last Updated August 28, 2020

References

Journal article

Insect tricks: two-phasic foot pad secretion prevents slipping

Journal of The Royal Society Interface | 16/09/2009 | J.-H. Dirks, C. J. Clemente, W. Federle

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