With spiders and silkworms taking center-stage, one could be fooled into thinking they were the only silk-producers around. However, there are at least 23 groups of insects and several other arthropods that have evolved to produce silk naturally.
Some of these creatures have developed innovative silks for some remarkable functions: deceiving, protecting, harnessing energy, and…creeping out neighborhoods. Ten of the most interesting of these are:
Hornets Thermoelectric Silk
When the eggs of the oriental hornet hatch, the larvae begin to secrete silk fibers which they weave into silk caps at the open end of their comb nest, thus immediately protecting them from the outside. The pupae continue spinning silk, forming a layer on the comb walls, and cocooning themselves for further protection.
However, what makes this silk remarkable is not its ability to protect the pupae from the harsh reality of predators but its extraordinary ability to behave as a thermoregulator: storing electrical charge during the day when there is excess heat and releasing the stored energy at night when the temperature drops. The double-stranded silk fiber is composed of an elastic protein called fibroin encapsulated by another protein called sericin, and it is thought this structure and composition, collectively give rise to the organic semi-conductor capabilities of the silk fiber.
Dance Flies Empty Balloons
During courtship or copulation some animals exchange nuptial gifts, ranging from nutritious gifts like insects or nuts to non-nutritional gifts like twigs – with the size of the gift being a huge determinant in how long copulation lasts and the likelihood of successful sperm transfer. The adult male dance fly is no exception and often wraps the prized possession in silk secreted from its dermal glands, located in its forelegs. The male dance flies then swarm together and become all macho as they try and outshine one another in an attempt to attract the female. However, what is interesting about dance flies is that in a few species the males (such as E. snoddyi) appear to have found a cunning way to get some action by offering no more than a cheap date.
Instead of finding a worthy gift to wrap in silk, which frankly takes up a lot of energy and time, E. snoddyi instead create “empty balloons made out of hundreds of silk bubbles”. Once the female has chosen a male, he will give her his silk balloon ahead of copulation. However, unlike other species who are distracted by opening and checking out their new gift, it appears the female E. snoddyi is content just holding onto her gift – a gift she later appears not to hold much value in as she drops it to the floor when copulation ends. It is still unknown how this “deception” entered this species but what we do know is that the males still need a silk balloon to get any kind of action.
Glowworms Twinkling Entrapment
In dark damp caves in New Zealand, there are gnat larvae who secrete silk from their mouth, creating a network of thin, double-stranded, silk threads.
Flash photo of glowworm. the light from it is washed out by the flash, but it is the right hand end (above the sticky thread) of the worm that lights up. Copyright Tony Wills
These threads, of variable length, dangle from the cave, and are coated at regular intervals with droplets of glistening, sticky mucus (that the larvae also secretes) – resembling crystal bead strands running through the cave.
Copyright Jon Sullivan
As the larvae move along the threads they begin to twinkle like fairy lights – thanks to the larvas ability to produce bioluminesence from their backside. This silk network makes for the perfect light show that lures predators, such as flying insects, into the cave, where they get entangled in the sticky silk. With the insect trapped and unable to escape, the larvae reel in their silk thread and consume their prey.
Lacewings Suspended Eggs
Eggs from the Australian Lacewing are easy targets for predators such as ants. In an attempt to circumvent this, adults push out a drop of silk, from their abdomen, onto the underside of a leaf, stretch it out to the point it stiffens, and then ‘bottoms’ it off with an egg. Voilà, just like that, the egg escapes detection, by being suspended from the leaf, and removed from the ants trail. The tough, unique, concertina door-like protein structure of the silk has an added benefit.
Green lacewing eggs hanging from Jasmine (Public Domain Pictures)
With its high lateral stiffness (nearly threefold that of silkworm silk), the silk suspension is able to stay on the leaf, resisting bending, which is great if you are an egg suspended in a windy area.
Shrimps Waterproof Glue
Until 2011 it was thought crustaceans were the only order within arthropods that did not have at least one silk-producing representative.
Silk produced from legs (BBC Nature)
However, this all changed when research scientists at Oxford Silk Group discovered a shrimp-like marine crustacea that had the ability to spin silk from its legs. The silk, which is saltwater resistant, has properties that allow it to be as adhesive as barnacle cement while also being flexible and as strong as spiders silk. These properties allow the silk to be the perfect underwater cement to build its tubular home from bits of algae, sand, vegetation, and (as gross as it is) faeces.
Caddisflies are thought to derive their name from the old English “cadice men”, vendors of yarns, braids, and threads, who displayed their material by pinning them onto their jackets – and if you look at the elaborate homes of these caddisfly, you can see why. Like the crustacea, mentioned above, caddisflies build their homes using their silk, which is also waterproof, however unlike the crustacea, caddisfly larvae secrete their silk from a pair of silk glands found in their spinneret (an organ which is by the side of their mouth), giving the extruded silk the appearance of a “double ribbon with a seam the long way”, and resembling a form of double-sided sticky tape. This ‘tape’ helps the larvae bind together bits of sticks, small stones, and other materials they find as they journey through their natural freshwater habitat, creating masterful architectural mobile homes. Their skill has not gone a miss either, artist Hubert Duprat utilized them to make some rather remarkable, bedazzling jewelery.
However, not all caddisfly species are inclined to be travelers, some prefer a more sedentary life and utilize their silk for another cool feat…food entrapment. The amazing resilience of their silk, which is able to stretch to twice its size, and then spring back slowly to its normal size, make it an ideal material to weave underwater nets. These nets which are set up on the upper surface of rocks (and other areas in their freshwater habitat) allow for easy capture and sieving of food as they stretch with great resilience as the water flows past them. The larvae alter the size of their nets in response to water flow and food abundance – large nets when there is a short supply of food in the area and small nets when there is fast flowing water.
Webspinners Live Life in Homemade Silk Tunnels
Larval webspinner in gallery. (Wiki Images)
Like spiders but unlike other insects, webspinners produce and use silk throughout their life. With over a hundred silk glands found in the swollen forelegs of webspinners, they are capable of quickly spinning large sheets of very fine silk (known as galleries) onto tree bark, beneath rocks and in leaf litter. They spend their lives under these silk sheets (females often stitch their eggs into the silk for protection and when they hatch they remain in the gallery and begin to spin silk) – expanding their food source by building new tunnels within galleries. Although little is known about these reclusive insects, we do know they have mastered a highly choreographed spin-step dance routine: spinning silk around the front and back of their body.
Not only are their spinning skills to be admired but the silk they produce is quite remarkable too: it is one of the finest silks in nature but is still capable of building very functional homes. Once the gallery-home is built, the silk behaves as a screen to predators, blocking the webspinner from sight and smell – the predators walk along the silk oblivious to the prey underneath; and the silk is waterproof, thus protecting the home during storms.However, the silk goes a step further as it does not just protect from rain but it harvests the water by sticking the droplets onto its surface – the bond is one of the “strongest adhesions to water of any natural hydrophobic surface”. The water droplet remains on the silk and can be later accessed by the webspinner who cuts a hole into the silk and drinks from the droplet.
Creepy Moth Caterpillar
Silk from Ermine Moth covering car in Rotterdam
If you happen to wake up to find your street and car looking eerily creepy, you may discover an ermine moth infestation. Like the webspinner, ermine moth caterpillars build large silk sheets which they use as protection while feeding. However, when several female adults lay their eggs in close proximity, it can results in hundreds of caterpillars spinning huge sheets, joining together to make superwebs. These superwebs have led to some alarming sights, including one where a tree-lined street in Rotterdam was covered in webs…engulfing a car with it.
Weaver Ants Silk Tool
Weaver Ant building nest with larvae silk. (Credit Wildsingapore)
What is innovative about these tree dwelling ants is that they use their larvae as a tool when building their nest. Ants work very well together, they are a great example of team work and what it can achieve. Weaver ants are no exception and are brought into the workforce from a very young age: constructing their nests by sticking leaves together using the glue of larvae.
Working cooperatively, the ants draw together leaves, closer and closer until they are perfectly positioned and close enough to stick (a chain of ants can be seen while this structural feat of engineering is commencing). Once ready, they pull out a rather cool “tool” – larva are taken from the queen’s chamber and sent to the construction site where workers squeeze them with their mandibles. The larvae release a fine sticky silk fiber from their labial gland, gluing the leaves together. This process continues over and over again, shuttling the larvae back and forth between leaves as a nest is woven together. Upon completion of the nest, the larvae are delivered to one of the new nests while the worker ants move on to more construction.
Genetically Engineered Goats
Randy Lewis with genetically modified goats. (Credit Utah State University)
Okay, so up until now, everything on this list has been an arthropod and evolved to produce its own silk; although this animal does not quite fit the bill, it is too extraordinary not to include, and that is because it is a goat. Although it is not a natural process and has needed a big helping hand from man – in this case it was one particular scientist, Randy Lewis – a small group of goats are now able to produce spiders silk protein.
For years humans have admired the spinning skills of spiders and have been particular fascinated by the strength of their silk, which is stronger than any man-made material and could have a huge impact in various medical and technological applications. However, spiders do not produce a lot of silk…certainly not enough for humans to produce anything significant, and scaling up quantities have a major limiting factor…spiders. Unfortunately, spiders are territorial and as such do not get on well with each other (preferring to kill each other) preventing any possibilities of farming them for silk. This has led to lots of innovations, in an attempt to scale up the production of spiders silk; including this one made by Lewis who decided to insert the silk producing gene from spiders into the genes of a goat, enabling the genetically engineered goat to produce the spiders silk protein in its milk. When the genetically engineered goats begin lactating, the milk is collected and the silk protein is purified in the lab (allowing silk fibers to be identified). This technique yields much larger quantities of silk fiber than could have been achieved through spiders. So far the goats that carry this gene have the same appearance and health as any ordinary goat and thus this innovation may well be the winning deal when it comes to producing spiders silk commercially.