This fortnightly
feature was published on August 16
The first land
animal
By Nutan Shukla
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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