The body surfaces of dung beetle normally have geometrically non-smooth or rough structures that will be useful to reduce contact area with soil and improve its hydrophobicity. As a result, both the adhesive and frictional forces between the animal body surface and the soil are reduced. The bionic research on anti-adhesion and resistance reduction of the non-smooth surface of dung beetles has been applied in agriculture, construction, mining and electric power, and has been extended to many engineering fields. It has obvious advantages in the multi-functional bionics in non-soil media, such as air, water, oil, and rock, showing their vast development potentials and extensive application prospect.

Dung beetles belong to the Coleoptera, superfamily Scarabaeoidea. After a long period of evolution, it has adapted to the sticky and wet environment. Dung beetles have a unique ability to dig holes. Generally, the depth of holes is over 80 cm, and some of them are over 2 m deep. The adult dung beetles are 40 mm to 80 mm long, oval, black, shiny, and hard. The clypeus is similar to bulldozer plate, and its cutting angle is 52°51'- 45° under normal conditions, and the cutting rear angle is 35°30'- 27°40', which is similar to the cutting angle range of the general bulldozer shovel. Its forefoot has evolved into a digging foot. Its tibia is broad and flat with hard teeth structures in edge, which like a rake and is suitable for excavation. 

Figure1 Various non-smooth morphologies on head and pronotum of dung beetle

The body surfaces of dung beetle normally have geometrically non-smooth or rough structures from macroscale to mesoscale or microscale, such as convex, concave, squama, ripple. The interactions between their nonsmooth body surface and the soil can produce microvibration effect, discontinuous water-film effect and air-film effect at the interface. This will generate microvibrations at the adhesion interface with certain frequencies and amplitudes, which will not only decrease the contact area and static contact time, but will also result in the discontinuous distribution of the water film, hence generating some air films in the interface between the animal body and the soil. As a result, both the adhesive and frictional forces between the animal body surface and the soil are reduced.

The shape of the clypei of dung beetle decreases resistance during earth cutting and burrowing. In addition, dung beetle can automatically reduce resistance by adjusting the wedge angle through rotation of its head to execute efficiently different functions such as bulldozing and earth cutting. By applying a biomimetic curved surface as the stress-bearing surface, adjusting the angle of the components, and switching between various soil-engaging components based on slide cutting principles, the soil-engaging components can be functionally optimized and structurally innovated to minimize resistance.

Figure2 Non-smooth Surface Model  Figure3 Interface state between ideal non-smooth surface and liquid

The bionic research on anti-adhesion and resistance reduction of the non-smooth surface of dung beetles has been applied in agriculture, construction, mining and electric power, and has been extended to many engineering fields. It has obvious advantages in the multi-functional bionics in non-soil media, such as air, water, oil, and rock, showing their vast development potentials and extensive application prospect.

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