Insects known as webspinners, in the relatively understudied order Embioptera, spin the finest silk fibers known in nature. They use that silk to build shelters that, when wet, form a strong, protective film. Here, an Antipaluria urichi webspinner spins silk. (Photo courtesy of Janice Edgerly, Ph.D.)

By Grant Bolton, Ph.D.

Grant Bolton, Ph.D.

If you were to think about silk-spinning creatures, you might imagine spiders toiling away on their webs. Or you’re picturing caterpillars that form cocoons, like Luna moths or the silk moth. Maybe you’ve got a little more entomology under your belt and you listed off weaver ants, caddisflies, or even some braconid wasps.

However, there’s another creature that is often overlooked when it comes to silk production. Webspinners, in the order , are secretive, soft-bodied insects that live tucked under bark or deep in leaf litter. They’re closely related to stick insects but quite distinct from them. Unlike spiders or caterpillars, webspinners don’t spin silk from their mouths or abdomens. Instead, they do it with their feet.

“Webspinners produce the world’s finest silk. That’s silk fibers on the nano-scale,” says Janice Edgerly, Ph.D., an insect behaviorist at Santa Clara University (SCU). “Some species have silk fibers between 35 and 40 nanometers in thickness. Many researchers have wondered how proteins can get that fine. So, we’ve looked at as many species as we could to see how their silks differ and what behaviors embiopterans have as they spin silk.”

Janice Edgerly, Ph.D.

Each front tarsus (the final leg segment, or foot, essentially) of a webspinner is outfitted with dozens of tiny silk ejectors that lay down fresh threads when they press down on surfaces, even their own silk. Webspinners can then build a tunnel system under bark that they use as both shelter and shield.

And for some species, that silk works like a raincoat.

Edgerly and SCU colleagues published a study in July in Environmental Entomology that explores how embiopteran silk interacts with water and whether webspinner species living in humid tropical forests weave silk with different properties than their dryland cousins.

To find out, Edgerly and her team compared silk from four webspinner species—two that live in the tropics on tree bark and two that dwell underground in dry environments. In the lab, the insects were encouraged to spin silk across grooved blocks. Once they had woven their shelters, the researchers placed tiny droplets of water onto the silk and used scanning electron microscopes to see what happened next. The results were striking.

“Something happens when water sticks to their silk,” Edgerly says. “Some of the silk in the tropics looks like a plastic film. An entire tree trunk in the tropics might be covered by this smooth silk film.”

Insects known as webspinners, in the relatively understudied order Embioptera, spin the finest silk fibers known in nature. They use that silk to build shelters that, when wet, form a strong, protective film. Here, scanning electron microscope images (recolored) demonstrate how the same patch of silk transitions from fibers to film for the tropical species Pararhagadochir trinitatis. (Photo courtesy of Janice Edgerly, Ph.D.)

As the team reviewed the results, they noticed distinct differences between the silk types. Silk from the tropical species, which live exposed on bark, was denser to begin with. In contrast, the dryland species spun looser, patchier silk that didn’t form as cohesive a film when wet.

The team also measured how much the silk repelled water by comparing contact angles of droplets. One of the dryland species, Haploembia tarsalis, had contact angles (a measure of how much water beads up on a surface rather than soaking in) nearly identical to a water-resistant control, while the other species showed more moderate water absorption. But, in all four species, the silk’s surface still changed when exposed to water, suggesting an interesting blend of water-resistant and water-absorbing properties.

Insects known as webspinners, in the relatively understudied order Embioptera, spin the finest silk fibers known in nature. They use that silk to build shelters that, when wet, form a strong, protective film. Shown here is a closeup of the tropical webspinner species Antipaluria urichi . (Photo courtesy of Janice Edgerly, Ph.D.)

Insects known as webspinners, in the relatively understudied order Embioptera, spin the finest silk fibers known in nature. They use that silk to build shelters that, when wet, form a strong, protective film. Here, Haploembia tarsalis silk galleries spill out from the insects’ hiding places in the crevices of a stone wall in the Santa Cruz mountains in California. An introduced species from the Mediteranean that is naturalized in California,  H. tarsalis webspinners graze on lichens and dried mosses. (Photo courtesy of Janice Edgerly, Ph.D.)

Insects known as webspinners, in the relatively understudied order Embioptera, spin the finest silk fibers known in nature. They use that silk to build shelters that, when wet, form a strong, protective film. Shown here is a field colony of the tropical webspinner species Antipaluria urichi in Trinidad. (Photo courtesy of Janice Edgerly, Ph.D.)

“Because of the protein components and structure, these silk fibers can almost trap water between their threads. It pins the water and holds it there. Eventually, the protein is solubilized into a thin film,” Edgerly says. “The silk changes into this shiny, beautiful patch. It’s slippery and hydrophobic, so water sheds off it like an umbrella. We’ve probably spent way too much time watching water dry on embiopteran silk!”

Webspinners are especially vulnerable to water when their silk tunnels flood, but the evolution of water-repelling silk has helped them adapt to these challenges in both tropical and arid environments.

This transformation from fiber to film could inspire new ways to create biodegradable coatings, nano-fiber textiles, or moisture-responsive materials in industry. With high crystallinity, extreme fineness, and the ability to interact dynamically with water, webspinner silk could help researchers design the next generation of bioengineered fabrics or smart surfaces.

Insects known as webspinners, in the relatively understudied order Embioptera, spin the finest silk fibers known in nature. They use that silk to build shelters that, when wet, form a strong, protective film. Here, water beads up on Antipaluria urichi silk, and over time the silk transforms to a film-like surface. As dry fibers or as transformed to a film by water, the silk protects the vulnerable insects inside their domicile. (Photo courtesy of Janice Edgerly, Ph.D.)

Beyond their silk, webspinners are full of surprises. While males are easier to identify by their wing venation, it’s the females that drive the show.

“Males don’t eat. They’re not part of the social dynamics. It’s the females that form these colonies, take care of their young, and have the interesting spinning behavior,” Edgerly says. “The females have a fascinating spinning routine they go through with over 10,000 steps!”

Edgerly’s work over the years has highlighted not just how webspinners use silk, but how intricate their lives truly are.

Grant Bolton, Ph.D., is a freelance writer and voice actor with a Ph.D. in entomology based in western Missouri. Email: [email protected].