Ecology

Beyond spiders: other silk insects

Anne Gageby
Strawberry Hill Nature Preserve

(5/2025) Spider silk is one of the most miraculous substances in the world. It has high tensile strength and extensibility which means it can withstand an immense amount of strain before breaking. Pound for pound, spider silk is stronger than steel. It can withstand temperature extremes down to -40 degrees Fahrenheit all the way up to 428 degrees Fahrenheit. Even more fascinating are its uses. Spider silk is used in mating rituals and can be used to transmit pheromones. It can be spun into an air-tight diving bell and, depending on the spider, can be used as a food source. It’s an incredibly unique substance in nature. Or is it?

Actually, no. The ability to produce silk isn’t uncommon. The ability to make silk occurs in most insect orders. The larvae of many insects that go through complete metamorphosis often make silk. This includes bees, butterflies, beetles, flies, and many more. And it doesn’t stop there. Some animals have adapted the same ability.

Spider mites, for example, produce webs used for transportation between plants. Their silk is especially fascinating in that it’s known as the thinnest natural silk fiber produced by silk spinning arthropods. That’s a blessing for them as spider mites can avoid detection until it’s too late and they’ve colonized an area, but a major problem for gardeners for the very same reason. And spider mites aren’t the only creature in a garden spinning webs. Even the often-pesky symphylans, sometimes called garden centipedes, use their silk to build nests and for defense.

Honeybee larvae use silk to reinforce the wax cells in which they grow. Bumblebee larvae spin cocoons within their wax hives and they save the cocoons for later pollen and honey storage. Similarly, oriental hornet eggs begin to secrete silk when they hatch. They weave this silk into caps at the open end of their comb which protects them from the outside. Their pupae continue to spin silk and eventually form a layer within the comb. This silk layer is quite remarkable because it protects the pupae from predators and acts as a thermoregulator. Oriental hornet silk stores electrical charge during the day and releases the heat at night as temperatures fall. This keeps the pupae comfortable with a well-regulated temperature as it develops.

One of our most popular programs at Strawberry Hill is Aquatic Communities. In this program we teach kids of all ages about aquatic macroinvertebrates such as water skippers, water pennies, and gilled snails. We also dive into the world of aquatic insects since many of the insects kids interact with spend their early lives in water. Damselflies, dragonflies, mayflies, etc. all begin as aquatic insects. But the one that piques kids’ interest is the caddisfly.

Caddisflies use silk to make a wide array of aquatic structures from stationary walls to mobile cases. The suborder Annulipalpia builds underwater structures between rocks and debris using their silk. These structures become retreats which afford them protection from predators while also providing a medium for collecting food. And they help channel oxygenated water over caddisfly gills thereby boosting the insects’ ability to absorb the critical gas. This is an incredibly significant adaptation for species adapted to living in lower oxygen environments.

Some species use their silk for other critically important uses. The larvae of the suborder Integripalpia build tiny portable cases that can be found clinging to the undersides of rocks. These cases give the larvae a protective shell that performs double duty as both camouflage and a physical barrier against predators. The cases are constructed of woven silk topped with tiny rock fragments, shells, leaf litter, and anything else the caddisfly can find. Their cases look like teeny tiny, decorated cones that are mobile.

One child commented recently that they reminded her of Tamatoa, the crab from Disney’s Moana. That was a fair assessment, in my opinion. Caddisflies aren’t gathering gemstones or collection ancient artifacts for the pageantry, but they are definitely building something beautiful. Interestingly, caddisfly casing jewelry is apparently a thing. Jewelry makers sometimes raise caddisflies and provide crushed gemstones and jewels for the caddisflies to use as building materials. When the caddisflies grow and move on, their glittering cases are abandoned and repurposed into earrings, necklaces, and so on.

All of the drama and sparkle aside, none of this would be possible without that fundamental building block, silk. Caddisfly silk is particularly unique in the world of arthropods due to its ability to remain sticky underwater. Caddisflies are related to Lepidoptera, the order that includes butterflies and moths and yet both of those insects produce dry silk. Silk is produced by a few other aquatic insects, but most silk-producers are terrestrial, so their silk does best outside of water. But not caddisflies’ silk. Theirs are designed to be sticky while entirely submerged. This has led some researchers to study caddisfly silk for its potential biomedical applications.

This can be confusing, however, because the word ‘silk’ is broadly applied to a variety of substances with vastly different chemical makeup. For example, fan mussels use a byssus, a bundle of filaments with silk-like threads to attach themselves to rocks under the sea. The byssus isn’t made of the same material as spider silk though it has similar properties. Carp use fibroin, a protein found in silkworm silk, to attach their egg clutches to rocks. Spider silk contains spidroin proteins, not fibroin. So, while they have similar properties and are used in similar ways, all silks are not the same.

No matter the uses or properties of silk the practicality of it is rather remarkable. Being able to produce the main component for housing material as well as food collection and storage would be amazing. Even better when that material can then be consumed as a source of nutrition after being used. It’s a wonderful adaptation that demonstrates nature’s creativity. And it’s not limited to spiders. Next time you’re outside and you find a caddisfly, a bumblebee, or even a garden centipede, take a second to appreciate the hard work they’ve already put in to make it this far. And give thanks to that miraculous material, silk.

Anne Gageby is the Environmental Education Manager of the Strawberry Hill Foundation. Strawberry Hill inspires stewardship of our natural world by
connecting the community with educational opportunities.
 Learn more by visiting StrawberryHill.org.