The stars of silk and the webs they weave

Silk is one of our oldest associations with bugs. It had been thought humans had been making use of silk for around 5000 years, but silk proteins have been found in 9500 year old tombs in Jihau, China, suggesting a much older relationship. Clothing silk comes from the cocoons of silk worm moths. The cocoon consists of a single strand of silk that may be up to 900m long. At around 10 microns in diameter, it’s much finer than a human hair. Many strands are woven together to make thread. 

Spider silk has also been used by humans in quite a variety of ways. Cross-hairs for gun sights and surveying instruments, dressings on wounds (silk has wonderful antimicrobial properties) and even fishing nets are just a few examples. Of course, it’s far easier rearing a lot of silkworms in a limited space than it is to do the same with spiders. Spiders like their space and eat other spiders that get too close. They’re really not that keen on having silk drawn from their spinnerets either!

Silk is a fibre mostly made up of proteins and a few other chemical components. It’s used quite widely in the bug world, but most bugs that use it are like the silk moth and use it for only one stage of their lives. The real masters of silk, are the spiders. From moment they emerge from their eggs (usually wrapped in silk), spiders are ready to put silk to use in a number of ways.

We can get a taste of that with the katipo is our Silk area star. You have to look up to see her as she’s high on a wall. This species is a member of the widow spiders, a group that includes more infamous cousins such as the black widow of North America and the Australian redback. However, as the smallest of this group and gives a proportionately smaller dose of venom in a bite. It’s unlikely to be fatal, but it may prove to be a deeply unpleasant experience. This species is also one of only two species of spider protected under The Wildlfide Act (the other is the Nelson cave spider). Once common up and down most of the sandy coastal dune systems of New Zealand, the geographic range of katipo has become fragmented over the years as we change the landscape.

Katipo can be found under driftwood and even litter like old cans, but their typical natural habitat is in the bases of native dune grasses. They can make use of introduced plants like marram grass, but eventually the plants thicken up too much and don’t allow enough room for the web. A katipo web has sticky elastic threads stretched out and anchored to the ground. Should a ground-dwelling insect like a beetle blunder into them, they snap and contract like a broken rubber band, lifting the prey off the ground and robbing it of traction.  The katipo plays out silk and wraps up the suspended prey in a nice neat bundle before delivering a bite. Silk also has a role in many other aspects of the life of a katipo. During mating, the male will secrete sperm on a special web. Eggs are wrapped up like a silken ball. If the spider is moving around it will play out silk as it goes, anchoring it every so often to make a safety line. Katipo spiderlings can even use silk to disperse to new areas. They’ll release silk that’s caught by a breeze that carries them aloft, eventually depositing them somewhere else.

While silk has a long history of use by humans, its remarkable properties mean the best is yet to come. Gram for gram it’s tougher than steel, it’s biodegradable and waterproof too. Scientists have been trying to crack the code of replicating silk for years and while they can’t quite do as well as a spider just yet, that doesn’t mean there aren’t any promising developments. At Tufts University they’ve taken the goo that gets spun as silk and turned it into 3D printer bio-ink. We’ve got a number of surprising examples of things made this way in the exhibition. However, this is only the beginning. Silk has potential in a vast array of applications including medicine, construction, bulletproof vests and even lasers! And who knows what incredible properties we might yet uncover from studying spider silk? Each spider can make a range of different silk types each with their own particular qualities, and this is also different for each species. We currently know of over 47000 different spider species with many more still awaiting discovery. That’s a huge array of silk types to study and learn from.

Dr Phil Sirvid looks after the entomology collection at Te Papa and has an inordinate fondness for spiders. He is one of the swarm of people that helped develop the Bug Lab exhibition.