Intricate silk helps net-casting spiders ensnare prey in webs

For spiders that fling their webs at prey, a sturdy net is essential.

A net-casting spider in search of a meal dangles upside down, holding a web in its legs before launching it at an unsuspecting insect. In the process, parts of the web can stretch to up to 24 times their original size in about a tenth of a second without breaking.

The web of the rufous net-casting spider (Asianopis subrufa) pulls off that feat thanks to looping strands that surround a stretchy silk core, researchers report in the Feb. 3 Proceedings of the National Academy of Sciences. Scanning electron microscope images revealed the spider silk’s intricate structure.

For most materials, there’s a tradeoff: Substances that stretch tend to break more easily. But the webs of these spiders manage to be both strong and stretchy.

As a strand stretches, the loops straighten, and those threads reinforce the core and prevent it from breaking. The spiders customize the amount of coiling in different sections of the web to account for how much each portion needs to stretch. The spider extrudes the loops of silk from a different set of glands than the core fiber, producing a sturdy material.

The resulting fibers are beautiful — but deadly.