Nothing like silk
Spiders are so needed, and yet so misunderstood. They have, in fact, coined a term to describe the fear of spiders! Arachnophobia! And yet, one can but marvel at the amazing shapes, geometric precision and quality of their spun webs.
We all turn up our nose at the sight of cobwebs in our homes and rush for the broom. But did you know that silk, which makes up these cobwebs, is the most unmatched natural fibre for its strength, ductility, smoothness and even beauty? Arachnids like spiders as well as a variety of insects produce silk, whose texture and property varies as per its use. It may astound you to know that the outermost strands of a spider’s web, the anchoring lines, are stronger than steel of the same dimension. The inner strands are of a different calibre – exceptionally sticky to catch and trap prey. If the prey is not to be eaten immediately by the web owner then it produces a different type of silk to wrap it up into a neat package by a rhythmic movement of its legs.
The aquatic spider (Argyroneta aquatic), builds its house out of waterproof silk, well anchored to the underwater plants. It then makes several trips to the water’s surface to fetch air globules which it releases under the silken sheet to give it a bell shape. The family of spiders live in this cosy home, surrounded by water. A dragline of silk is produced by some spiders and caterpillars to escape enemies or even by jumping spiders to avoid falling all the way down. It reminds one of bungee jumping. When the threat dissipates, this bungee jumper eats up its own silk strand to reach its original perch. Meanwhile, the Bola spiders swirl a line of silk with a gluey blob at its end to capture their prey. One species of Bolas, the magnificently coloured Dicrostichus magnificus, a very fussy eater, only feeds on a particular moth species and that too, only the male. So as soon as the hapless prey arrives, drawn by the scent of the female moth that the spider cunningly emits, it uses its bola to capture and enjoy its meal.
You may have come across opaque white silk sheets attached to the surface of leaves. If you dare to lift one end and take a peek, you may be surprised to see hundreds of baby spiderlings sitting pretty inside. These spiderlings, once they have stepped out of their nurseries, often disperse far and wide—they have been found on ships across miles of ocean and on mountains 3000m high. How did they reach there? They use a mind-boggling technique called ‘ballooning’. The first climb to the highest tip of a plant, producing fine silken lines all the time, till they finally feel a tug when the lines are about to snap. They then begin to get wafted by the winds, the silken lines providing buoyancy, much like our hot-air balloons or parachutes.
Among insects, the mulberry silk moth (Bombyx mori) has made history. It was the Chinese who first discovered that a kilometre-long silk strand could be unwound from the moth’s cocoon if the latter was first killed by putting in boiling water. They spun silk robes for the royalty and guarded their secret zealously for many years. They began trading their silk for other wares with other countries, daring to travel on camelback through dangerous terrains. That is how the historic Silk Route was laid down. Ironically, the Bombyx has been cultivated by man to such an extent that the moth has now completely lost its instincts to survive in the wild.
Large numbers of Tent Moth caterpillars live in silken tents that they construct. At night they all crawl out to forage for food, sleeping blissfully in their tents during the day. Some, like the Golden Angle or Banded Awl caterpillars, use silk as glue to make shelters by turning over the leaf margins or rolling up leaves respectively. The Weaver Ant larvae produce silk by which several leaves are joined edgewise to make nests. Birds borrow the cobwebs made by others to line their nests. The very first tailor on our planet, the Tailor Bird, deftly uses its beak to spin thread out of cobwebs and then stitches leaves together for its young ones. Man, as always, has attempted at mimicking this miracle creation of nature. But artificial silk is no match to this fascinating biodegradable material.
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