Adaptive camouflage: What can be learned from the wetting behaviour of the tropical flatbugsDysodius lunatusandD. magnus

Abstract

The neotropical flat bug species Dysodius lunatus and Dysodius magnus show a fascinating camouflage principle, as their appearance renders the animal hardly visible on the bark of trees. However, when getting wet due to rain, bark changes its colour and gets darker. In order to keep the camouflage effect, it seems that some Dysodius species benefit from their ability to hold a water film on their cuticle and therefore change their optical properties when also wetted by water. This camouflage behaviour requires the insect to have a hydrophilic surface and passive surface structures which facilitate the liquid spreading. Here we show morphological and chemical characterisations of the surface, especially the cuticular waxes of D. magnus. Scanning electron microscopy revealed that the animal is covered with pillar-like microstructures which, in combination with a surprising chemical hydrophilicity of the cuticle waxes, render the bug almost superhydrophilic: water spreads immediately across the surface. We could theoretically model this behaviour assuming the effect of hemi-wicking (a state in which a droplet sits on a rough surface, partwise imbibing the structure around). Additionally the principle was abstracted and a laser-patterned polymer surface, mimicking the structure and contact angle of Dysodius wax, shows exactly the behaviour of the natural role model – immediate spreading of water and the formation of a thin continuous water film changing optical properties of the surface.

Passive water collection with the integument: mechanisms and their biomimetic potential

“…The South American flat bug species Dysodius lunatus and Dysodius magnus collect water for camouflage, in which they reduce their surface reflectivity, rather than rehydration (Silberglied and Aiello, 1980;Reiswich, 2013;Hischen et al, 2017). Immediate spreading of water droplets is facilitated by chemical and structural Patchwork of hydrophilic and hydrophobic parts Wetting properties of elytra, gravity Hamilton and Seely, 1976;Seely, 1979;Nørgaard and Dacke, 2010 Onymacris bicolor* Seely, 1979;Nørgaard and Dacke, 2010 Stenocara sp.…”

“…In general, the need for water collection is often for rehydration, but it is also needed for water adsorption, which prevents dehydration of the skin (Lillywhite and Licht, 1974). Furthermore, collected water serves the thermoregulation in elephants and wharf roaches (Hoese, 1981;Lillywhite and Stein, 1987), is transported by adult sandgrouse from water sources to hydrate the young (Cade and MacLean, 1967), and yields reduced reflectivity for camouflage in flat bugs (Silberglied and Aiello, 1980;Hischen et al, 2017).…”

Transparent laser-structured glasses with superhydrophilic properties for anti-fogging applications

“…Examples of superhydrophilic surfaces can be found in nature, e.g., on various plant surfaces [4], lizards [5], or tropical flat bugs [6]. These kind of structures were mimicked on glasses by deposition of nanoparticles [7,8] or (1) cos = r cos 0 .…”

The external scent efferent system of selected European true bugs (Heteroptera): a biomimetic inspiration for passive, unidirectional fluid transport

“…There are many examples that go beyond simple passive interaction. Nature has come up with a variety of systems that allow for influencing of body-surface fluids in very specific ways: lizards harvesting moisture and directing fluid passively to their mouths [ 7 , 8 ] and female fleas being able to direct fluids passively within their spermatheca [ 9 ], or camouflage based on getting wet or staying dry, as observed on the neotropical flat bug Dysodius magnus [ 10 , 11 ], are only a few examples for this. Especially when we have a closer look into the class of insects, the most common interaction is the repellence of water on the surface.…”