Evolutionary Ecology Research, 2001, 3: 567-581

© 2001 Brent D. Opell

Changes in the mechanical properties of

capture threads and the evolution of modern

orb-weaving spiders

Brent D. Opell1* and Jason E. Bond2

1Department of Biology, Virginia Tech., Blacksburg, VA 24061 and 2Department of Zoology

Insect Division, Field Museum of Natural History, Roosevelt Road at Lake Shore Drive,

Chicago, IL 60605, USA

ABSTRACT

The capture threads of spider orb-webs retain prey and contribute to a web's ability to absorb

the forces generated when prey strike the web. Primitive orb-webs produced by the Deinopoidea

clade are horizontally oriented and contain dry, fuzzy (cribellar) capture thread, whereas

modern orb-webs constructed by the Araneoidea clade are vertically oriented and contain

viscous adhesive threads. Independent contrast analyses found no relationships between spider

mass or features of web architecture and the tensile strengths, Young's moduli and breaking

energies of capture threads. Cribellar and adhesive threads have similar breaking energies, but

the manner in which they resist breaking differs. The tensile strengths and Young's moduli

of adhesive threads are smaller than those of cribellar threads, rendering adhesive threads

weaker, but better equipped to dissipate force by stretching. This mode of absorbing force is

advantageous for vertical orb-webs, which typically intercept faster flyying prey than horizontal

orb-webs. The greater extensibility of adhesive capture thread allows an orb-web to dissipate

energy locally as capture threads stretch while transferring force and also enhances the web's

overall extensibility, allowing it to flex and dissipate force through air resistance.

Keywords: adhesive thread, breaking energy, character evolution, cribellar thread, tensile

strength, Young's modulus.