Whip spiders (Amblypygi) become water-repellent by a colloidal secretion that self-assembles into hierarchical microstructures.

Jonas O. Wolff,Stanislav N. Gorb,Michael Seiter,Thomas Schwaha

doi:10.1186/s40851-016-0059-y

Abstract

BackgroundAmong both plants and arthropods, super-hydrophobic surfaces have evolved that enable self-cleaning, locomotion on water surfaces, or plastron respiration. Super-hydrophobicity is achieved by a combination of non-polar substances and complex micro- and nano-structures, usually acquired by growing processes or the deposition of powder-like materials.ResultsHere we report on a multi-phasic secretion in whip spiders (Arachnida, Amblypygi), which externally forms durable, hierarchical microstructures on the basically smooth cuticle. The solidified secretion crust makes the previously highly wettable cuticle super-hydrophobic. We describe the ultrastructure of secretory cells, and the maturation and secretion of the different products involved.ConclusionWhip spiders represent intriguing objects of study for revealing the mechanisms of the formation of complex microstructures in non-living systems. Understanding the physical and chemical processes involved may, further, be of interest for bio-inspired design of functional surface coatings.Electronic supplementary materialThe online version of this article (doi:10.1186/s40851-016-0059-y) contains supplementary material, which is available to authorized users.

Highlights

Among both plants and arthropods, super-hydrophobic surfaces have evolved that enable self-cleaning, locomotion on water surfaces, or plastron respiration
We found that the whip spider integument is covered with a crust of a solidified secretion that forms globular microstructures with a diameter of 0.3
The secretion is present on all body parts, except regions situated close to and at joint membranes and segment borders, the distitarsi and pretarsi of legs, parts of the chelicerae and the eyes. It may be absent on the tips of tubercles that widely cover the dorsal cuticle of the carapace and parts of the legs

Summary

Introduction

Among both plants and arthropods, super-hydrophobic surfaces have evolved that enable self-cleaning, locomotion on water surfaces, or plastron respiration. Super-hydrophobicity is achieved by a combination of non-polar substances and complex micro- and nano-structures, usually acquired by growing processes or the deposition of powder-like materials. Because small water droplets form a nearly spherical shape, they roll off the surface at a tilted angle below 10° [8]. The report of this phenomenon in plants in the late 1990s [1] generated enormous interest in waterrepellent and self-cleaning surfaces, and led to innovations in artificial super-hydrophobic materials and surface. There are many drawbacks in the production of such materials, and especially the durability of such coatings is often not satisfying [10].

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