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September 23, 2018

Spider's unique engineering techniques

Wolf-spider. Photo/STEVE KINUTHIA
Wolf-spider. Photo/STEVE KINUTHIA

Over the last two weeks since the rains started pounding the country – our region not excepted – I have had occasional visitors in my house. The guests are not the kinds of people who you can ask to stop visiting. They are insects that, though I profess my love for animals, I try as much as possible to resist loving them. They are neither beautiful, nor of any use in my house. Indeed, these visitors pose danger to their hosts, especially a crawling infant.

My guests are spiders. And they come in plenty. Big spiders, small ones, some with blunt colours and some with patterned bodies. I have had to buy a large broom made of tough twigs to help eliminate the menace, but they keep coming. They hide under the rugs at the doorstep and some manage to crawl under the main carpet in the living room. I have tried trimming the grass in the garden, even spraying them with insecticides, but they still keep coming. Now I am on the verge of giving up. I think I will just have to train my family on how to avoid them and let them, exhaust their visit and leave my house.

The spider clan, an ancient group called Araneida, are some of the most uncommon creatures ever to evolve on earth. They are among the most numerous of the insects. According to naturalist WS Bristow, who took an impromptu census, he found 2.2 million individuals within less than an acre of land. You can imagine how many visitors I have if I live on an eighth of an acre.

Spiders are not popular within the human circles. But our lives may be dependent on them and other insects – in that, they spend their entire lives snaring and devouring insects, which if left to multiply, may become hazardous to our lives. They are found virtually everywhere on the planet. No climate is rugged for the clan Araneida. They can be found at 22,000 feet above sea level on Mt Everest, and also at 2,000 feet below sea level. Being pioneers among creatures who left the sea to forge new lives on land, they have highly developed nervous system, brains capable of memory and a remarkable engineering ability.

The spider’s talent for spinning silk and making nets is one of the most common miracles of nature. It is said the silk has a tensile strength far greater than steel, and only second to quartz. Spider silk can be stretched as far as fifth of its length before it snaps. A strand that we see with the naked eye is usually composed of several tiny threads. A single thread may be too small to be seen without visual aids like a microscope or a magnifying glass.

All spiders have a nipple-like structure called spinnerets, usually three pairs, located at the end of the abdomen. On each spinneret are a number of minute orifices through which the secretion of the silk glands is expelled. When spinning a web, the tips of the spinnerets are brought together so that the streams of secretion unite into a single thread. He starts by making the first line of silk, called “the bridge” which is suspended more or less horizontally. The weaver may attach the strand to the top of blade of a tall grass, drop down with it and go up on another blade of grass and attach the other end of the strand, and then pulls tight. The bridge is done.

Some weavers just leave one end of the strand to the power of the wind and let it attach to anything. Once attached, the weaver may only need to strengthen the attached point and tighten the strands. From either side of the bridge, the spider brings down another strand and joins them at a junction to make a triangle.

From the three corners of the triangle, the weaver makes other strands and joins them in the middle of the triangle. Then he starts making circles at the centre, called a hub. Around the hub, the spider builds a temporary inner spiral to give him a hold while he spins the outer circles. All this time, and all what the spinner has done so far, is building a skeleton. This skeleton is non sticky. From here, the rest of the spinning will be very sticky silk, which is what is used to catch prey.

To be continued...

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