Free-standing spider silk webs of the thomisid Saccodomus formivorus are made of composites comprising micro- and submicron fibers

Christian Haynl,Thomas Scheibel,Hendrik Bargel,Mark A Elgar,Mark J Tobin,Jitraporn Vongsvivut,Kai R H Mayer,Vanessa J Neubauer

doi:10.1038/s41598-020-74469-z

Abstract

Our understanding of the extraordinary mechanical and physico-chemical properties of spider silk is largely confined to the fibers produced by orb-weaving spiders, despite the diversity of foraging webs that occur across numerous spider families. Crab spiders (Thomisidae) are described as ambush predators that do not build webs, but nevertheless use silk for draglines, egg cases and assembling leaf-nests. A little-known exception is the Australian thomisid Saccodomus formivorus, which constructs a basket-like silk web of extraordinary dimensional stability and structural integrity that facilitates the capture of its ant prey. We examined the physical and chemical properties of this unusual web and revealed that the web threads comprise microfibers that are embedded within a biopolymeric matrix containing additionally longitudinally-oriented submicron fibers. We showed that the micro- and submicron fibers differ in their chemical composition and that the web threads show a remarkable lateral resilience compared with that of the major ampullate silk of a well-investigated orb weaver. Our novel analyses of these unusual web and silk characteristics highlight how investigations of non-model species can broaden our understanding of silks and the evolution of foraging webs.

Highlights

Our understanding of the extraordinary mechanical and physico-chemical properties of spider silk is largely confined to the fibers produced by orb-weaving spiders, despite the diversity of foraging webs that occur across numerous spider families
We reveal that micro- and submicron fibers, exhibiting a distinct chemical composition, yield threads that are extraordinarily resilient against lateral loads compared with the major ampullate silk of orb webs
The moths of the family Urodidae build cage-like, protective c ocoons[34,35,36], which seem to possess a similar dimensional stability compared with the webs of S. formivorus

Summary

Introduction

Our understanding of the extraordinary mechanical and physico-chemical properties of spider silk is largely confined to the fibers produced by orb-weaving spiders, despite the diversity of foraging webs that occur across numerous spider families. A little-known exception is the Australian thomisid Saccodomus formivorus, which constructs a basket-like silk web of extraordinary dimensional stability and structural integrity that facilitates the capture of its ant prey. We showed that the micro- and submicron fibers differ in their chemical composition and that the web threads show a remarkable lateral resilience compared with that of the major ampullate silk of a well-investigated orb weaver. Crab spiders (Thomisidae) are typically described as ambush predators, remaining concealed in the vegetation before seizing their prey, but do not build foraging webs[15,16,17,18] These spiders produce draglines and attachment d iscs[19], form egg cases and use silk to construct protective leaf nests[15]. We further reveal that the base of the basket web contains spider eggs: this is arguably the first documented example of an elaborate spider foraging web that has evolved as an extension of the protective egg case

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Conclusion