Daily experience shows that a spider that stays in the center of an orb-web is able to orient itself immediately toward the prey, and capture it, by testing the web at the contact points of its eight legs. Although this is one of the key aspects in the study of spider behavior, the prey catching problem still remains a mystery to a large extent. Previous investigations on dynamic signal transmission through the web caused by prey’s impact focused mainly on one-dimensional models of vibration transmission, typically along a single radial thread, and progress was limited by the lack of two-dimensional models of wave propagation in the orb-web. The first continuum membrane model of a spider orb-web was proposed only in 2017 by Morassi, Soler and Zaera (A continuum membrane model for small deformations of a spider orb-web, Mechanical Systems and Signal Processing, volume 93 (2017) pp. 610–633). In this theory, the actual discrete web, formed by a finite number of radial and circumferential threads, was approximated by a continuous elastic membrane on the assumption that the spacing between threads is small enough. The membrane has a specific fibrous structure, which is inherited from the original discrete web, and it is subject to tensile pre-stress in its referential configuration.
Basing on the continuous membrane model of orb-web, Professor Antonino Morassi from the University of Udine in Italy, in collaboration with Professor Alexandre Kawano at the University of São Paulo in Brazil, developed the first systematic investigation of the prey’s localization problem from dynamic measurements in an orb-web that mimic those made in Nature by a spider. Their work was published in the research journal Mechanical Systems and Signal Processing.
In their approach, Kawano and Morassi used advanced inverse methods of source identification in the membrane orb-web model to show how the mechanical response induced by prey’s impact can be used by the spider to localize the prey, for spiders that stay in the central hub of their web. Specifically, the authors developed a reconstruction algorithm based on the knowledge of the transverse deflection time history at the eight spider legs immediately after the impact. Their results – while performed on a realistic family of orb-webs supported at the boundary – revealed that the dynamic signals propagating through the orb-web immediately after impact contain sufficient information to the spider to capture the prey. The two researchers also reported that the reconstruction of the prey location was rather stable with respect to changes of the input data.
In summary, the study reported on the development of an algorithm for reconstructing the impact region of the prey that is based on a realistic description of the information accessible to the spider in Nature. The approach reported here is substantially different from those available in the literature and can offer valuable insights into understanding how the spider can predict the position of the prey. In a statement to Advances in Engineering, Professor Alexandre Kawano and Professor Antonino Morassi mentioned that their results can offer valuable insights for studying the prey catching problem in other different classes of orb-webs. In addition, from a technical perspective, the benefits that stand to be ripped upon unravelling of the mystery of the prey’s catching problem in an orb-web, may involve numerous real-life applications, including the design of sustainable robust fiber networks and large-scale tensile fiber structures – among others.
Alexandre Kawano, Antonino Morassi. Can the spider hear the position of the prey? Mechanical Systems and Signal Processing, volume 143 (2020) 106838.