Ů��С��Ƶ

It’s a spider-eat-spider world. High-speed cameras have recorded the first footage showing how ground spiders hunt other spiders – sometimes bigger than themselves – by tying them up with sticky silk.

Ground spiders, members of the Gnaphosidae family, include 2000 species found all over the world. Unusually, they don’t build webs, instead chasing down their prey and fighting them head-to-head.

To learn more about their hunting technique, Jonas Wolff of Macquarie University in Sydney, Australia and his colleagues put ground spiders in a container with other spiders or crickets and filmed them from below.

Strong grip

In some cases, the ground spiders didn’t use silk at all, instead gripping the prey directly with their front legs and overwhelming it. More often, they tried this technique first but quickly switched to using silk if the prey turned out to be too large. The spiders stuck silk to the floor of the container before running around their prey quickly, sticking the thread to the prey’s legs as they went.

Ground spiders produce this silk in organs called piriform glands. Most spiders use piriform silk to attach the structural threads of their webs to surfaces. In ground spiders, the piriform glands are enlarged and modified to enable them to extrude a thick layer of glue very quickly.

The tubes that extrude the silk are usually retracted inside the body, but when the spider launches an attack, they inflate. This mechanism helps to prevent the tube from getting clogged up.

Taking on bigger prey is undoubtedly a high-risk strategy. One of the spider species Wolff’s team studied counter-attacked by biting the ground spider, and sometimes succeeded in killing the predator. “The risk is there and they can only reduce it by entangling and quickly immobilising the prey, but that doesn’t mean they can totally diminish the risk,” says Wolff.

Superglue silk

Wolff and his colleagues also revealed the material properties of ground spiders’ piriform silk for the first time. The silk is so sticky that collecting pieces of it to analyse is quite a challenge. “The single fibres are extremely small and they stick to the ground; that’s their purpose,” says Wolff. “We used some polymer foam so we could get the silk off without damage.”

The silk combines the properties of superglue with the elasticity of silk fibres. When the prey struggles, it pushes against the silk, but the elasticity means the silk won’t break and the prey remains stuck. “That’s something we don’t have in artificial glues,” says Wolff.

He hopes to study piriform silk in other types of spiders to learn more about how they attach their webs to objects. “I think we could learn a lot from how spiders attach silk when it comes to applying glue or designing adhesives,” he says.

It’s an outstanding study, says Stano Pekar of Masaryk University in Brno, Czech Republic. “Gnaphosids are, however, an extremely diversified family and not all species have such a silk gland configuration, so it remains to be investigated in the future which factors, trophic or environmental, shaped the evolution of this attack tactic.”

Journal reference: Journal of Experimental Biology, doi:10.1242/jeb.154682

Read more: Spiders can hear you walking and talking from across the room

Spiders eat twice as much animal prey as humans do in a year