Hunting spiders lose web skills

Adaptations to create sticky traps leaves ground spiders without a safety harness.

Ground spiders (Gnaphosidae) specialize in catching prey that fights back fiercely, including ants and other spiders. They snare their prey with an unusually glue-like silk, which evolved from a thread normally used to anchor a web’s structural silks to surfaces.

Jonas Wolff at Macquarie University in Sydney, Australia, and his colleagues studied 11 species in slow-motion video and examined the biomechanics of their silk and silk-producing structures.

The researchers found that as the gluey silk evolved into a hunting tool, the glands that produce it became bigger, while those that make the main thread shrank. As a result, these ground spiders can no longer spin abseiling ‘draglines’ and are barely able to attach webs to the environment.