Today we will talk about a class of animals, called Arachnids. They are easily distinguished from insects by their four pair of legs. Unlike insects, which are plenty in almost every part of the world, Arachnids are less in number. And out of many different animal species which come under the class of Arachnids, spiders are largest.
So, how these spiders find their food? As we all know, their solution to this problem is, constructing a web. Spider cannot be everywhere at the same time, but a net or a web increases its reach and can catch more insects.
Different species of spiders exist and different types of web shapes also. Some species do not build web at all, and some build circular webs, funnel shaped webs, tangled cobwebs, triangular webs etc. But let’s focus on a circular or orb web for now.
So, how does an orb-weaver spider actually make its delicate web? Surprisingly, the whole process takes about an hour or two. It has nearly seven to eight different silk producing organs (or spinnerets) underside, and there are different glands connected to it for producing silk of varying protein composition. These different types of silk are used in making different parts of the web.
The process, more or less goes something like this: first, the spider starts by flying a silk thread like a kite. The thread is very light and if there is a soft blowing wind, it clings to some surface. It spins another thread and walks along the previous thread tying it down there again. Then it travels to the middle of this second thread and due to its weight the thread takes a V like shape. There, it starts another thread, which it then ties down to some leaf or branch. So now we have a Y like shape. The three spokes of the web are ready. The next step would be to draw all remaining spokes from the center of Y in all directions, called radial threads. After completing the spokes it builds a spiral from center to outward. Then walking along that spiral again, it builds another spiral from outside which is sticky.
Now that we have a perfect orb-web, how do we know that it’s actually going to work. Let’s say a little insect flies into it, it may tear the entire web. So, to catch the insects, the web should be elastic. And it should be sticky too otherwise the insect may bounce off the web. And, the good thing is that the spiders have solution to all these problems.
We know that the spiral part of the web is sticky. When you zoom into these sticky silk thread, you will find a lot of bead like structures there, which are actually tangled threads inside a drop of liquid. The liquid is not just water but a sticky glue and hence it serves two purposes: the tangled threads of the spider silk inside the liquid gives it extra length, and it also helps in capturing the flying insects which stick to it.
In the end, let’s talk about the gossamer silk, another fine and very light silk produced by spiders. Some spiders use it to fly, which is known as spider ballooning. Spider first checks the air current using one of its legs and then shoots the silk threads. Within seconds it’s flying in the air. Although, it’s not quite obvious if spiders can actually control where the silk threads will take them, yet they cover very large distances.
This blog post is inspired by Silken Fetters, a chapter from Richard Dawkins’ awesome book, Climbing Mount Improbable