Ruud Kleinpaste
Ruud Kleinpaste marvels at the soft and flexible, yet incredibly strong and tough, contraptions that are manufactured by nursery web spiders.
The Bugman explains how and why spiders spin their soft-as-silk web.
at about this time last year, I spotted a Dolomedes female, walking around with a sizeable ball of silk in her mouth. I love Dolomedes and I love silk, so that observation totally made my day!
The nurseryweb spider is a creature you don’t see very easily and often, unless you know what to look for. Their famous nurseries, however, are everywhere; pure white and sizeable contraptions made of the sturdiest quality of silk, and suspended in the tips of gorse bushes and grasses in the New Zealand landscape.
Now everybody knows exactly what I mean.
The backstory to this observation is truly remarkable though, and it is about the way these spiders create such magnificent nurseries for their kids. It’s all to do with the story of silk, technology and construction in the light of a circular economy.
Silk is a versatile proteinaceous material that is made by a number of invertebrate groups on the planet. Caterpillars use it to create cocoons (silkworms) or to descend from a tree down to the soil for pupation (including leafrollers).
Case moths use silk to construct the most impenetrable, cigar-shaped body armour for developing caterpillars. Some Hymenoptera (ants) use silk, as do mites and embioptera (an obscure group of small critters that have silk glands in their forearms).
But spiders take silk to a whole new level. Literally.
When young spiders grow to the stage of having to disperse from the area they were born in, they go ballooning.
This is an extraordinary process of standing on tippy toes and producing whole swathes of very fine strands of silk into the air.
The wind picks these threads up and blows them skywards.
The spiderling will hold on to their leaf for a while, waiting for conditions to be just perfect for takeoff. Then it’s just a matter of letting go and drifting up into the breeze.
Recent studies reveal that it’s not just the wind that assists this form of dispersal (even relatively heavy spiders can take off in the smallest of breezes) but that the earth’s vertical atmospheric electrostatic field may be playing a serious part in this too. It creates electrostatic buoyancy for the silk as well.
As a result, these wingless invertebrates can reach altitudes of a few kilometres on their more or less random journey.
This random trajectory can have serious drawbacks, you may think. What about landing in water, for instance?
This could be a problem, although we now know that some spiders are equipped with Teflon-like legs and can easily walk on a watery surface and literally “sail” with their legs.
What’s more, some spider species can use silk to anchor their floating body to a particular point in that liquid habitat!
So far, we’ve already seen a number of examples of spiders’ use of silk. But there’s far more to the story than this.
Spiders often have a whole series of spinnerets (their silk-spinning organs) and these are festooned with heaps of “spigots” that slowly press out the liquid protein strands, which
Imagine being able to literally create all sorts of stuff from a very light and flexible material that comes from some glands on your bum!
immediately set (on contact with air) into stretchy but strong silk filaments, ready for use. Individual spiders can thus produce up to seven types of silk, all used for different technology or construction. Imagine that: being able to literally create all sorts of stuff from a very light and flexible material that comes from some glands on your bum! Our Dolomedes mother already had done some of the prep work on her egg sac: the dozens of eggs were positioned in the softest nursery silk, which was contained in a sturdy covering of much harder silk and shaped in a perfect ball.
The next thing was to create a larger pouch to hang in a gorse bush. For that, she needed to select a silk nozzle that creates a spacing silk, which needed to be protected by a cover silk, that also needed a rainproof outer layer.
And when all of that was finished, the whole contraption needed to be tethered to the gorse bush. When you find an old, used nursery web in autumn, have a look. Pull it apart and marvel at the incredible technology and silk types involved.
And you know what? I have never ever heard a female Dolomedes exclaim “Bugger!” when she accidentally engages the wrong spigots on her spinneret! ✤