quinta-feira, 12 de abril de 2012

Caught In The Web

Imagine you are an insect caught in a spider web. What exactly will happen to you once the spider comes and, as it were, sits down beside you? It’s not a pretty process, that’s for sure but some amazing macrophotography can make even death a thing of beauty...

The fate of a creature caught in a spider web often holds a morbid fascination to the casual viewer. The urge to release them may be strong but many hold back, perhaps afraid that if they assist the struggling animal then a similar fate may well be in store for them.

Yet once you are caught in the web, what exactly is it that happens? Hold on to your hat and perhaps your breath too – and if you are at all squeamish perhaps you should not read on. Murder most horrid, at which perhaps even Agatha Christie might blanch, is about to take place.

Let’s get one thing straight right away – all spiders are poisonous. Not that you should run screaming from a room the minute you see one – the spiders in your house generally will not have enough poison to do you any harm whatsoever. In fact, they will not even be able to pierce your skin. Generally. Size isn’t everything but most are way too small to do you any damage.

A few, of course, have bites that may put you in to the morgue but these are few and far between. That is, though, a digression – this is all about the small insects and other invertebrates (such as the poor snail above) that somehow make it in to the web.

One of the first questions asked is why on earth insects and such can’t escape from spider’s web. The answer is they do – in fairly large numbers – the poor creatures you see here are those that, despite no doubt their best efforts, were unable to get away from the ravenous beastie that created the web in which they floundered.

If every single insect that becomes caught in a web were to be greedily devoured then spiders would indeed be fat little creatures. They might have to appear on reality TV in a pseudo celebrity spider fat club type of show in which they would have weekly confessionals about how little they have eaten (while no doubt skulking back to their rooms to munch on a hidden lady bug or two).

A spider makes its silk in certain glands in its abdomen. Then it is forced through many tiny holes at the tip of the abdomen. It comes out as a liquid but immediately becomes solid when it comes in to contact with the oxygen in our air. There are lots of different silks made by spiders and they use them in a variety of ways, from making their houses, lassos, spring traps and even diving bells. However, we will concentrate mostly on the wondrous orb webs we see every day.

Some insects are lucky and escape, but why doesn’t a spider get caught in its own web? Well, some of the silk is sticky and some of it is, well non-stick as it were. No guesses for which type of silk the spider steps upon when it traverses its web. Stickiness is a big issue. If the silk is too sticky then the trapped insect would not be able to set itself free but its struggles might ultimately destroy the web. So the spider designs its web so that part of the spiral can detach rather than break, so saving the entire web and ensuring that the insect, flaying around for its life, will repeatedly adhere to the silk.

An insect may still escape, however. Webs can be busy places and the spider chooses its prey carefully. Once that prey is singled out it will disable it with a bite, clambering quickly over the web to reach it. It sounds like a form of cannibalism, one insect eating another, but it must be remembered that spiders are not insects. They are from a group that is closely related known as arachnids. The big difference is that they have eight legs and no wings. Can you imagine if there were flying spiders? Your Auntie Agnes wouldn’t leave the house.

Spiders, not surprisingly, do not chew but they must be forgiven their table manners mostly because they have no teeth as we would know them and also because they are, well, spiders. Once they have located their prey they bite it. Then they inject venom in to their victim. Of course, the venom is harmless to the spider itself - a question that some ask is why doesn’t their own venom kill them. If that were the case they would be up for one of those Darwin awards).

Now that the insect has been injected with venom, the looking at the TV screen between your fingers part of the story really begins. The venom will either kill the insect or paralyze it – either way they are going nowhere fast. The insides of the insect will then, inexorably, turn to liquid, leaving their outer shell intact, kind of a flask for the mushy nutrition inside. The spider, once the venom is doing its job, will wrap the insect in silk.

Sometimes, however, the hunter can become the hunted.  Here a spider is devoured by a wasp. Yet more often than not, the spider rules supreme in the web.

If a spider is hungry then it will drink the liquid on the spot. If not, then it will tie the bundle of silk holding the mortal remains of its prey to the web and pop back for a snack later – or perhaps that should be called a night cap, the remains being in liquid form, after all. Sometimes all that is left is a single wing, a reminder of what was once so full of life.

You may even consider that the gruesome demise of these insects could be seen as actually doing us a favor. Spiders, after all, eat many more insects than birds (if the global populations of the two are taken in to account) and can often do away with biting insects, such as yellow flies, which just love to bite humankind. Some people scream if a spider accidentally alights on their person. Can you imagine what the spider might be thinking, being flicked or even squished by a monster many times its size? Believe me, if you were a bus it would want to get off.

Of course, if spiders were our own size there is little doubt what would happen…

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