Sunday, August 16, 1998
The first land animal
EVERYBODY knows that scorpions are vicious creatures, but the females of the species are loving and caring mothers. As the young scorpions are born, their mother carefully twists her pincers to provide them an easy climb up. The young clamber slowly up the claws and then they hold on to her back as tightly as they can with their own tiny pincers. Packed closely together they ride with her for several days and if they are accidentally knocked to the ground she stops and searches for them.
When she finds them she waits while they climb back up again before setting off once more. After a few days the young jump off and fend for themselves. If danger threatens the young while they are on their mothers back, the female will defend them from enemies by threatening them with her sting-tipped tail.
Among these arachnids, during mating, the male deposits its sperm in a small mucus packet, the spermatophore, and leaves it on the ground. After this clasping the females claws with his own, taking care not to get stung by her tail, he manoeuvres her carefully over his dropped sperm and these are picked up by the cloacal lips of the female, thus enabling internal fertilisation. Usually it is believed that all scorpions lay eggs, while the fact is that the members of the family scorpionidae are viviparous, they produce living young instead of eggs.
Being the most primitive arachnids, scorpions have been recorded from the Silurian Period (beginning 430 million years ago and terminating 35 million years later). A Silurian scorpion was perhaps the first terrestrial (land) animal. The number of eyes varies up to 12 in some scorpions, but their vision is poor, many species being nocturnal and equipped with sensory hairs to detect prey. Their sensory organs include slit sense organs, sensory setae (stiff hair-like structure) as well as peculiar comb-like structures with innervated tips responding to touch and vibration frequencies above 100 Hz.
These arachnids are usually yellow to brown or black, more rarely greenish or bluish, and all are fluorescent in ultraviolet light. Most scorpions sting in defense or to subdue their prey, and although the poison may be strong and even effective against vertebrates, they themselves are immune against it. Members belonging to the family Buthidae are dangerous to humans because the poison is neurotoxic in action, which means the toxin that affects the functioning of the nervous system.
There are 700 or so known species of scorpions, most of which are tropical and subtropical. Of these species Pandinus imperator of Africa is the largest scorpion reaching 170mm in length.
These creatures may chew their food, which they hold with large pincers called pedipalps. The chewing is not so much to break up the prey into small pieces as to release its fluids. These are sucked in by the scorpions sucking pharynx. This is the fore-part of the gut and has a number of muscles attached to it. When the muscles contract, the pharynx expands and lowers the pressure inside it, drawing the liquid in through the mouth. Spiders suck their prey in a similar way.
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