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Tuesday, November 30, 2010

Spiders defence defence strategies strategies

ByCheong Ah Kwan

BEFORE the advent of online Spiderman games, little boys used to hunt down the real McCoys, put them carefully in small matchboxes and primed them for sport.
These ‘fighting spiders’, known to display aggressive behaviour when put together with another of its species, were trophies by themselves to be flashed at potential opponents in contests. A champion spider
could elevate a young boy’s status more than a few notches.
Joseph Koh, the current High Commissioner of Singapore to Brunei, was one of those little boys who carried around matchboxes with a prized spider in each of them.
What began as a simple hobby turned into a life-long passion.
His book on the spiders of Singapore has gained him recognition as the authority in the region.
The Malaysian Nature Society Kuching Branch has never had an expert talk about spiders and it was indeed a rare treat to have the mysteries of some of these spectacular web sites unravelled.
Spiders have an array of predators ranging from birds, frogs, wasps and other spiders.
As a result, these arachnids have evolved a host of defence strategies to protect themselves.
Some of these strategies to escape predation are ingenious and include camouflage, the building of shelters, intimidation with threat posture and the use of mimicry.
Camouflage is a very common defence strategy and we are not unfamiliar with animals that can blend into their surroundings to render themselves invisible to potential enemies. In fact, this is such an effective strategy that human beings have exploited the technique in warfare.
Spiders that resemble tree nodes are often found sitting on the bark or branch of a tree.
The wraparound spider simply ‘vanishes’ by wrapping itself around a twig during the day.
Instead of constructing webs, some spiders build shelters or burrows on the ground.
The entrance to such contraptions is often plugged with leaves and pebbles during the rainy season to protect against flood waters.
The waterproof trapdoor also keeps uninvited guests at bay.Most spiders possess great agility that enables them to escape with speed when danger lurks. Some slower moving spiders do play dead when they feel threatened.
CAMOUFLAGE: The bird-dropping spider takes mimicry to a whole new level.

The use of intimidation as a defence strategy is relatively common.As a deterrence to their enemies, many spiders are armed with thorny projections and may be colourful in their appearance in an effort to present themselves as unpalatable.
Defensive stances and threat postures such as the spreading open of legs, raising the body and exposing fangs are used to intimidate potential enemies.
Of all the defence strategies employed by spiders, the most fascinating one has to be that of mimicry.
Spiders have fantastic mimicry that they employ for protection as well as hunting.
To escape predation, several species of spiders have resorted to ant mimicry.
Ants are known to be unpalatable because of the formic acid they contain, and it is therefore advantageous to look like them.
In protective mimicry, these eight-legged creatures wave their forelegs in the air to fake antennae reducing the number of functional legs to six. In addition, their bodies also seem appropriately segmented to look like an insect.
Very often, protective mimicry extends into aggressive mimicry whereby the spiders use anatomical and behavioural ant mimicry to hunt ants.
Their stunning deception gets them accepted into ant colonies which they willlater destroy. The bird-dropping spider
takes disguise to a whole new level. It not only looks like bird dropping on a leaf, but comes complete with a wafting odour of dung. Such a devious strategy is effective against birds and wasps.
The smell is a plus as it attracts flies which are devoured.
The macro photographs of the spiders projected onto the big screen during Koh’s talk were a feast for the eyes. Certainly the Spiderman weaved us into his multi-dimensional web.
As we queued to sign up for the night walk to hunt for spiders, he promised a session on the feeding strategies of our eight-legged friends when he returns.
Meanwhile, to all the Miss Muffets out there, do stock up on curds and whey.

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