Join us on a journey into the silent world of
scorpions, fascinating creatures that thrive in the most remote corners of our planet. The realm
of these arachnids extends from mountains to plains, from deserts to the rocky crawlways of the
tropics and subtropics. Today, we explore their amazing anatomy, which makes them the perfect
hunters of the night. From the fine sensors of their pedipalps to their deadly stingers, every
aspect of their body tells a story of adaptation and survival in a world full of challenges.
Scorpions belong to the class Arachnida and are part of the phylum Arthropoda. There are an
estimated 1,750 to 2,500 species of scorpions worldwide, of which only about 25 are considered
potentially lethal to humans. This impressive diversity is also reflected in their size, from
the tiny Typhlochactas mitchelli, which barely reaches 9 millimetres, to the imposing emperor
scorpion, which can be up to 21 centimetres long. These primitive land arthropods are known
for their remarkable evolutionary resilience and adaptability to extreme conditions.
The body of the scorpion consists of two main parts: the anterior prosoma or cephalothorax
and the posterior opisthosoma or abdomen.
The prosoma is made up of five fused
segments with six pairs of appendages, including chelicerae, pedipalps and four pairs
of walking legs. The eyes are also located here, with one pair of simple median eyes and two
to five pairs of lateral eyes on the sides.
The opisthosoma consists of two parts: the wider
mesosoma or pre-abdomen with seven segments and the narrower, tubular metasoma or post abdomen
with five segments. The mesosoma harbours two special structures, the genital opercula and
the pectines, a pair of comb-like organs.
The metasoma ends in a venomous sting
consisting of the telson and the aculeus. The telson harbours the paired venom glands.
The aculeus, a sharp stinger hardened by heavy metals such as zinc and iron, allows the scorpion
to inject its venom into prey or attackers efficiently. This venom consists of a complex
mixture of neurotoxic peptides and serves both to paralyse prey and to protect it from predators.
Particularly remarkable is the ability of scorpions to adapt the composition of
their venom depending on the threat or type of prey and even to produce a
"pre-venom" with different properties.
Although scorpions can deter some potential
attackers due to their venom, they are still vulnerable to predators such as owls, bats,
snakes, lizards and others who will take the sting for a savoury meal. Certain scorpion
species, particularly in the Buthidae family, exhibit sexual cannibalism, where
females consume males after mating.
The digestive system of scorpions begins in the
preoral cavity, a chamber-like structure at the front end of the cephalothorax. Here, prey is
grasped and crushed by the powerful chelicerae, supported by the pedipalps. The food is then
transformed into a liquid broth, similar to spiders, by secreting enzymes to break down the
prey and absorb the nutrients. The crushed food slurry then enters the mouth, which is a small
transverse opening in the preoral cavity. From here, it leads to the pharynx, a muscular
sucking piston that transports the food into the oesophagus. The salivary glands, positioned
on either side of the oesophagus, produce saliva, which further breaks down the food.
The midgut is the main player in this digestive process. It consists of a small stomach
that merges into a long, narrow intestine. This intestine is divided into the anterior mesosomal
and the posterior metasomal intestine. This is where the actual digestive work takes place.
Finally, the undigested remains are collected in the hindgut and excreted through the anus.
The hepatopancreas, also known as the scorpion's liver, is an impressive organ that occupies
the dorsal part of the abdominal cavity. This glandular mass has a dual function: it
produces digestive enzymes and digests, similar to the pancreas. Its secretion reaches
the intestine via 5-6 pairs of hepatic ducts.
It also stores nutrients such as glycogen and
fats, regulates the water balance and can even store metals such as copper and lead.
It also influences the reproductive cycle of female scorpions by providing nutrients and
water during pregnancy to support the embryos.
The excretory system of scorpions comprises
Malpighian tubules and coxal glands. The Malpighian tubules are fine tubes that
are attached to the intestine and absorb nitrogenous waste products from the haemolymph
and transport them into the intestine.
The coxal glands, near the base of the third leg,
also function as excretory organs. They consist of an end sac, a spiral tube and a bladder that
channels waste products out through a duct.
The scorpion's respiratory system consists of
lungs that enable them to utilise atmospheric oxygen efficiently. These lungs consist
of four pairs and open through stigmata, narrow slits on the sternum of the third to
sixth pre-abdominal segments. The structure of the book lungs is fascinating. They are
compressed sacs with an inner membrane folded into numerous fine leaflets. This increases
the surface area for gas exchange enormously. Gas exchange takes place through the rhythmic
expansion and contraction of the abdomen.
The heart of the scorpion extends over
several segments of its back. It has ostia, small openings, that regulate the blood flow. The
scorpion's haemolymph, which serves as a blood substitute, is indigo-coloured and transports
the respiratory pigment haemocyanin.
The nervous system of scorpions consists of a
central nervous system, a peripheral nervous system and a visceral nervous system. The
central nervous system comprises the brain, suboesophageal ganglia and a double ventral
ganglionic nerve cord. The brain is located directly under the middle eyes in the prosoma and
controls complex behaviours such as hunting.
The peripheral nervous system extends
from the ganglia of the central nervous system and sends nerve impulses to
the sensory organs and extremities to help scorpions explore their environment,
hunt and defend themselves from danger.
The visceral nervous system autonomously controls
important bodily functions such as heart rate, respiration and digestion, which enables scorpions
to react quickly in fight or flight situations.
The sensory organs of scorpions include
eyes, pectines and sensory hairs, which are distributed over the body.
Scorpions have a fascinating eye configuration with two median eyes and up to ten lateral eyes,
supplemented by a light-sensitive sensor in the metasoma. The median eyes on the carapace provide
clear vision and spatial resolution thanks to a visible lens and photoreceptor cells surrounded
by light-sensitive rhabdomeres and pigment cells. The lateral eyes, without a vitreous body and
connected by rhabdomeres, offer less optical acuity but act as highly sensitive light sensors.
These specialised eyes enable scorpions to detect differences in brightness even in dim light.
The pectines, comb-like limbs of the scorpions below the walking legs, are covered with
tooth-like projections on which hundreds of pin-shaped, sensitive sensory organs, the
so-called pegs, are located. These structures are primarily responsible for chemical perception
by picking up chemical signals, such as odours and pheromones, from the environment with the
help of 100,000 sensory neurons. In addition, the pectines act as mechanosensors that detect
physical changes in the substrate, such as surface structures or ground vibrations. This ability
enables the scorpions to explore their environment and detect prey or mates.
Scorpions are asexual.
The male reproductive system
consists of testicles, vas deferens and other specialised structures.
The female system comprises an ovary, oviducts and a common genital chamber. Fertilisation is
internal, and most scorpions are viviparous, with embryos being nourished in the womb.
In the secretive realm of scorpions, complex mating behaviour takes place, including
a ritualised dance, the promenade à deux. Male scorpions use visual, mechanical and
chemical signals to attract females. They recognise potential mates using pheromones,
which are perceived by their pectines, and also differentiate between pregnant and
non-pregnant females. The mating dance culminates in the transfer of the spermatophore from the
male to the female. Some species even reproduce parthenogenetically. Scorpions are viviparous,
with different forms of prenatal development: apoicogenic and catoicogenic. After
birth, the young spend their first stage of life on their mother's back,
where they receive protection and care.
Scorpions go through up to nine moults
in their lifetime in order to grow and reach sexual maturity. This process, during
which they emerge from their old exoskeleton, is crucial for their development. The first moult
takes place on the mother's back, and the young scorpions are particularly vulnerable. After
the last moult, which marks sexual maturity, the moult cycle ends. Scorpions have the
potential to live for 15 to 25 years or even longer due to their slow metabolic rate.
In the nocturnal deserts, scorpions display a fascinating green-blue fluorescence under UV light
that covers their entire cuticle and remains even after their death. Scientists have discovered
that special chemical compounds in the cuticle are responsible for this glow. The exact function
is still unclear, but it is thought that the fluorescence may play a role in UV detection.
Our journey through the mysterious world of scorpions ends but leaves us with a deep
understanding of these amazing creatures. Their role as natural hunters helps to maintain the
ecological balance. The scorpions teach us respect and admiration for the small but mighty heroes
of our ecosystems and encourage us to appreciate the diversity and beauty of life on our planet.
Thank you for joining us today to learn more about the fascinating world of scorpions. If you want
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