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1. Triangle weaver spiders construct spring-loaded webs using a novel set of genes for exceptionally proline-rich silk

   https://doi.org/10.1093/pnasnexus/pgaf318  

   Casey, Steven; Correa-Garhwal, Sandra M; Baker, Richard H; Stafstrom, Jay A; Reeve, Hudson Kern; Hayashi, Cheryl Y; Garb, Jessica E (October 2025, PNAS Nexus)

   Ma, Li-Jun (Ed.)

   Abstract Spiders amplify their physical capabilities by synthesizing multiple high performing silks. Renowned for its toughness, major ampullate (MA) silk composes the spiderweb frame, providing support and absorbing high-energy impacts. In ecribellate orb-weavers, proline-rich motifs in MaSp2 proteins of MA silk are linked to a range of mechanical properties, including extensibility, elasticity, stiffness, and supercontraction. We show a modification of these motifs outside of this clade in a spider that constructs a spring-loaded web. The triangle weaver spider Hyptiotes cavatus (family Uloboridae) stores energy in the support lines of its triangular web, then rapidly releases the tension to catapult forward, collapsing the web around prey. Hyptiotes has an expanded set of MaSp2 genes which encode proteins with far higher proline contents than typical MaSp2. The predominant GPGPQ motifs present in Hyptiotes spidroins also occur abundantly in MaSp sequences of distantly related spiders that produce the most extensible dragline, implying silk protein convergence. Proline-rich MaSp2 proteins constitute half of all MA gland expression in Hyptiotes, and we show that the resulting fibers are the most proline-rich spider silk measured to date. This unique silk composition suggests a functional importance that may facilitate the spring-loaded prey capture mechanism of this species' web and may inspire the design of novel biomaterials using protein engineering. 

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2. Behavior and Bioadhesives: How Bolas Spiders, Mastophora hutchinsoni, Catch Moths

   https://doi.org/10.3390/insects13121166  

   Diaz, Candido; Long, John H. (December 2022, Insects)

   Spiders use various combinations of silks, adhesives, and behaviors to ensnare and trap prey. A common but difficult to catch prey in most spider habitats are moths. They easily escape typical orb-webs because their bodies are covered in sacrificial scales that flake off when in contact with the web’s adhesives. This defense is defeated by spiders of the sub-family of Cyrtarachninae, moth-catching specialists who combine changes in orb-web structure, predatory behavior, and chemistry of the aggregate glue placed in those webs. The most extreme changes in web structure are shown by bolas spiders, who create a solitary capture strand containing only one or two glue droplets at the end of a single thread. They prey on male moths by releasing pheromones to draw them within range of their bolas, which they flick to ensnare the moth. We used a high-speed video camera to capture the behavior of the bolas spider Mastophora hutchinsoni. We calculated the kinematics of spiders and moths in the wild to model the physical and mechanical properties of the bolas during prey capture, the behavior of the moth, and how these factors lead to successful prey capture. We created a numerical model to explain the mechanical behavior of the bolas silk during prey capture. Our kinematic analysis shows that the material properties of the aggregate glue bolas of M. hutchinsoni are distinct from that of the other previously analyzed moth-specialist, Cyrtarachne akirai. The spring-like behavior of the M. hutchinsoni bolas suggests it spins a thicker liquid. 

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3. The evolution of siphonophore tentilla for specialized prey capture in the open ocean

   https://doi.org/10.1073/pnas.2005063118  

   Damian-Serrano, Alejandro; Haddock, Steven H.; Dunn, Casey W. (February 2021, Proceedings of the National Academy of Sciences)

   null (Ed.)

   Predator specialization has often been considered an evolutionary “dead end” due to the constraints associated with the evolution of morphological and functional optimizations throughout the organism. However, in some predators, these changes are localized in separate structures dedicated to prey capture. One of the most extreme cases of this modularity can be observed in siphonophores, a clade of pelagic colonial cnidarians that use tentilla (tentacle side branches armed with nematocysts) exclusively for prey capture. Here we study how siphonophore specialists and generalists evolve, and what morphological changes are associated with these transitions. To answer these questions, we: a) Measured 29 morphological characters of tentacles from 45 siphonophore species, b) mapped these data to a phylogenetic tree, and c) analyzed the evolutionary associations between morphological characters and prey-type data from the literature. Instead of a dead end, we found that siphonophore specialists can evolve into generalists, and that specialists on one prey type have directly evolved into specialists on other prey types. Our results show that siphonophore tentillum morphology has strong evolutionary associations with prey type, and suggest that shifts between prey types are linked to shifts in the morphology, mode of evolution, and evolutionary correlations of tentilla and their nematocysts. The evolutionary history of siphonophore specialization helps build a broader perspective on predatory niche diversification via morphological innovation and evolution. These findings contribute to understanding how specialization and morphological evolution have shaped present-day food webs. 

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4. Stabilized Morphological Evolution of Spiders Despite Mosaic Changes in Foraging Ecology

   https://doi.org/10.1093/sysbio/syac023  

   Wolff, Jonas O; Wierucka, Kaja; Paterno, Gustavo B; Coddington, Jonathan A; Hormiga, Gustavo; Kelly, Michael B; Herberstein, Marie E; Ramírez, Martín J (March 2022, Systematic Biology)

   Rosindell, James (Ed.)

   Abstract A prominent question in animal research is how the evolution of morphology and ecology interacts in the generation of phenotypic diversity. Spiders are some of the most abundant arthropod predators in terrestrial ecosystems and exhibit a diversity of foraging styles. It remains unclear how spider body size and proportions relate to foraging style, and if the use of webs as prey capture devices correlates with changes in body characteristics. Here, we present the most extensive data set to date of morphometric and ecological traits in spiders. We used this data set to estimate the change in spider body sizes and shapes over deep time and to test if and how spider phenotypes are correlated with their behavioral ecology. We found that phylogenetic variation of most traits best fitted an Ornstein–Uhlenbeck model, which is a model of stabilizing selection. A prominent exception was body length, whose evolutionary dynamics were best explained with a Brownian Motion (free trait diffusion) model. This was most expressed in the araneoid clade (ecribellate orb-weaving spiders and allies) that showed bimodal trends toward either miniaturization or gigantism. Only few traits differed significantly between ecological guilds, most prominently leg length and thickness, and although a multivariate framework found general differences in traits among ecological guilds, it was not possible to unequivocally associate a set of morphometric traits with the relative ecological mode. Long, thin legs have often evolved with aerial webs and a hanging (suspended) locomotion style, but this trend is not general. Eye size and fang length did not differ between ecological guilds, rejecting the hypothesis that webs reduce the need for visual cue recognition and prey immobilization. For the inference of the ecology of species with unknown behaviors, we propose not to use morphometric traits, but rather consult (micro-)morphological characters, such as the presence of certain podal structures. These results suggest that, in contrast to insects, the evolution of body proportions in spiders is unusually stabilized and ecological adaptations are dominantly realized by behavioral traits and extended phenotypes in this group of predators. This work demonstrates the power of combining recent advances in phylogenomics with trait-based approaches to better understand global functional diversity patterns through space and time. [Animal architecture; Arachnida; Araneae; extended phenotype; functional traits; macroevolution; stabilizing selection.] 

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5. Mechanics of the Prey Capture Technique of the South African Grassland Bolas Spider, Cladomelea akermani

   https://doi.org/10.3390/insects13121118  

   Diaz, Candido; Roff, John (December 2022, Insects)

   Spiders use various combinations of silks, adhesives, and behaviors to ensnare prey. One common but difficult-to-catch prey is moths. They easily escape typical orb-webs because their bodies are covered in tiny sacrificial scales that flake off when in contact with the web’s adhesives. This defense is defeated by spiders of the sub-family of Cyrtarachninae—moth-catching specialists who combine changes in orb-web structure, predatory behavior, and chemistry of the aggregate glue placed in those webs. The most extreme changes in web structure are shown by the bolas spiders which create only one or two glue droplets at the end of a single thread. They prey on male moths by releasing pheromones to draw them close. Here, we confirm the hypothesis that the spinning behavior of the spider is directly used to spin its glue droplets using a high-speed video camera to observe the captured behavior of the bolas spider Cladomelea akermani as it actively spins its body and bolas. We use the kinematics of the spider and bolas to begin to quantify and model the physical and mechanical properties of the bolas during prey capture. We then examine why this species chooses to spin its body, an energetically costly behavior, during prey capture. We test the hypothesis that spinning helps to spread pheromones by creating a computational fluid dynamics model of airflow within an open field and comparing it to that of airflow within a tree, a common environment for bolas spiders that do not spin. Spinning in an open environment creates turbulent air, spreading pheromones further and creating a pocket of pheromones. Conversely, spinning within a tree does little to affect the natural airflow. 

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