Choreography of silk spinning by webspinners (Insecta: Embioptera) reflects lifestyle and hints at phylogeny

Silk spinning defines the morphologically constrained embiopterans. All individuals spin for protection, including immatures, adult males and the wingless females. Enlarged front tarsi are packed with silk glands and clothed with ejectors. They spin by stepping with their front feet and releasing silk against substrates and onto preexisting silk, often cloth-like. Spinning is stereotypical and appears to differ between species in frequency and probability of transition between two spin-step positions. This spinning choreography was assessed using thousands of spin-steps scored in the laboratory for 22 species to test: (1) the body size hypothesis predicting that spinning would be more complex for larger species; and (2) the phylogeny hypothesis which predicted that spinning would display phylogenetic signal. Tests relied on published phylogenies for the order Embioptera. Independent contrast analysis revealed relationships between five spin characteristics and body size, whereby, for example, larger webspinners invested in relatively larger prothoracic tarsi used for spinning and in spin-steps that would yield expansive silk coverings. Spin-step dynamics displayed a phylogenetic signal for the frequency of six spin-steps and for 16 spin-step transitions. Discussion focuses on patterns revealed by analysis of phylogenetic signal and the relationship to life style and to recently discovered chemical characteristics of silk

The spinning apparatus of webspinners – functional-morphology, morphometrics and spinning behaviour

Webspinners (Insecta: Embioptera) have a distinctly unique behaviour with related morphological characteristics. Producing silk with the basitarsomeres of their forelegs plays a crucial role in the lives of these insects – providing shelter and protection. The correlation between body size, morphology and morphometrics of the spinning apparatus and the spinning behaviour of Embioptera was investigated for seven species using state-of-the-art methodology for behavioural as well as for morphological approaches. Independent contrast analysis revealed correlations between morphometric characters and body size. Larger webspinners in this study have glands with greater reservoir volume, but in proportionally smaller tarsi relative to body size than in the smaller species. Furthermore, we present a detailed description and review of the spinning apparatus in Embioptera in comparison to other arthropods and substantiate the possible homology of the embiopteran silk glands to class III dermal silk glands of insects