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

Abstract

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.

Insects as zoogeomorphic agents: an extended review

“…The Embioptera (webspinners) are members of a small order of insects and live in small colonies in subterranean nests of silk‐lined burrows and galleries (Downing, 2008). The same behaviour of maternal care is observed in the webspinner females, which typically guard the eggs in the burrows and protect them with a silk covering, a particular behaviour shared with burrowing wolf spiders (McMillan et al ., 2016).…”

“…Semi‐social and unsocial insects can also dig complex systems of deep tunnels. The gregarious webspinners (Embioptera) produce networks of silk‐line galleries that can form an extensive tunnel system of aggregated nests (McMillan et al ., 2016). Crickets and mole crickets (Orthoptera: Gryllidae and Gryllotalpidae) individually construct tunnel networks of relative complexity up to 60 cm long (Figures 1D and 6D).…”

Structural and wetting properties of nature's finest silks (order Embioptera)

“…The webspinners are soft-bodied and flexible, and the females are always wingless as shown in figure 1 b ; these features allow them to easily run backwards and forwards within their tightly spun silken tunnels. With stereotypical stepping patterns [ 11 ], they create protective silken domiciles on trees ( figure 1 c ) in humid climes. In dry regions, they live in leaf litter or in underground burrows, which they line with silk.…”

Silk Spinning Behavior Varies from Species-Specific to Individualistic in Embioptera: Do Environmental Correlates Account for this Diversity?

“…2 Downloaded from https://academic.oup.com/isd/article-abstract/4/2/2/5824810 by University of Cambridge user on 13 May 2020 Variation in spinning behavior by adult female embiopterans appears to hold clues about phylogenetic relationships or adaptations related to lifestyle that are not easily observed (McMillan et al 2016). Spinning routines have proven to be very long; individual females display many hundreds, even thousands, of spinsteps executed during hour-long filming sessions (McMillan et al 2016). When spinning, they step with their front feet, swollen with silk glands, and release silk by pressing hair-like ejectors against the substrate (Ross 2000;Fig.…”

“…When they pull their foot back, the silk protein is sheared into nano-scale fibers (Okada et al 2008, Addison et al 2014, Stokes et al 2018), dozens produced with each footfall. The spinning routine includes up to 28 different spin-steps with the right and left front leg placed one step at a time around the body (Edgerly et al 2002;McMillan et al 2016). They spin over and around their dorsum (dubbed 'dorsal spinning') and then turn to face the emerging structure to thicken that with more silk (dubbed 'ventral spinning').…”