Abstract
Among the different species of flower beetles, there is one of particular notoriety: the Goliath beetle. This large insect can grow up to 11 cm long and is well-known for its distinctive black and white shield. In this paper, we focus on a particular Goliathus species: G. orientalis (Moser, 1909). We investigated the variations in properties of both the black and white parts of the upper face of G. orientalis; more precisely, the variation in surface properties with respect to the wettability of these two parts. This work reveals that the white parts of the shield have a higher hydrophobic character when compared to the black regions. While the black parts are slightly hydrophobic (θ = 91 ± 5°) and relatively smooth, the white parts are highly hydrophobic (θ = 130 ± 3°) with strong water adhesion (parahydrophobic); similar to the behavior observed for rose petals. Roughness and morphology analyses revealed significant differences between the two parts, and, hence, may explain the change in wettability. The white surfaces are covered with horizontally aligned nanohairs. Interestingly, vertically aligned microhairs are also present on the white surface. Furthermore, the surfaces of the microhairs are not smooth, they contain nanogrooves that are qualitatively similar to those observed in cactus spines. The nanogrooves may have an extremely important function regarding water harvesting, as they preferentially direct the migration of water droplets; this process could be mimicked in the future to capture and guide a large volume of water.
Highlights
Insect species are ubiquitous and have a significant influence across most of the world
While the black parts were slightly hydrophobic (θ = 92◦ ), the white parts were highly hydrophobic (θ = 131◦ ) with strong water adhesion, similar to what is observed on rose petals
The analysis of the surface roughness and morphology shed light on the hypothesis that the difference in surface wettability observed may be related to the different structures found on the elytra surface
Summary
Insect species are ubiquitous and have a significant influence across most of the world. Insects need to adapt to a wide diversity of environments. Throughout centuries of evolution, insects have managed to adapt perfectly to various environmental stresses specific to these different locales. The success of these adaptations has made insects a very relevant subject of investigation, as well as an infinite source of inspiration for scientists [1,2,3,4,5,6,7,8,9]. Swimming insects need to be perfectly hydrophilic to preserve their hydrodynamic properties and move through an aqueous environment as efficiently as possible [3]
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