Slingshot spiders build tensed underdamped webs for ultrafast launches and speedy halts

TL;DR

This study presents a mathematical model of slingshot spider webs, revealing how their conical shape and tension lines enable ultrafast launches and quick halts through underdamped oscillatory dynamics and viscous silk drag.

Contribution

The paper introduces a 2D-coupled damped oscillator model that explains the web's dynamic behavior, highlighting the dual role of tension lines and viscous silk in spider predation and self-preservation.

Findings

Web acts as elastic spring and shock absorber

Tension line enables rapid loading and halting

Viscous silk drag dissipates energy efficiently

Abstract

We develop a mathematical model to capture the web dynamics of slingshot spiders (Araneae: Theridiosomatidae), which utilize a tension line to deform their orb webs into conical springs to hunt flying insects. Slingshot spiders are characterized by their ultrafast launch speeds and accelerations (exceeding 1300 $m/s^2$), however a theoretical approach to characterize the underlying spatiotemporal web dynamics remains missing. To address this knowledge gap, we develop a 2D-coupled damped oscillator model of the web. Our model reveals three key insights into the dynamics of slingshot motion. First, the tension line plays a dual role: enabling the spider to load elastic energy into the web for a quick launch (in milliseconds) to displacements of 10-15 body lengths, but also enabling the spider to halt quickly, attenuating inertial oscillations. Second, the dominant energy dissipation mechanism is viscous drag by the silk lines - acting as a low Reynolds number parachute. Third, the web exhibits underdamped oscillatory dynamics through a finely-tuned balance between the radial line forces, the tension line force and viscous drag dissipation. Together, our work suggests that the conical geometry and tension-line enables the slingshot web to act as both an elastic spring and a shock absorber, for the multi-functional roles of risky predation and self-preservation.