CyberDodo and Spiders (1-56)

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This is a curious yet appropriate question, since we identify insects because they have 6 legs and yet spiders have 8. Furthermore, insects mainly have a body composed of 3 parts, but spiders only have 2. So, contrary to what many people think, spiders are not insects, they belong to the class of arachnids (Aranae).

What are the main characteristics of spiders?

We already know that they have 8 legs and a body divided into two parts, beginning with the anterior (front), which is called the prosoma or cephalothorax (That is, the "head" and "chest") which houses the brain, eyes (most often it has 8 of them), a stomach, a "mouth" which is surrounded by two pairs of "tools", firstly the chelicerae ending in hooks with which the spider bites its prey and injects its venom and, secondly, the pedipalps which are used to recognise and catch prey. The 8 legs are also attached to the cephalothorax .

The posterior (rear) is called the opisthosoma or simply the abdomen. It contains the lungs, heart, liver, sexual organs and glands that produce silk.

The front and rear are interconnected by a much thinner section: the pedicel, which contributes to the flexibility of the spider’s body.

Are males and females the same size?

There may be some species of spiders with large physical differences, where the male is much smaller than the female. This is significant sexual dimorphism.

Are spiders hairy?

Not only are they hairy, but they are covered by different types of hairs. These are proper sense organs which transmit a great deal of information about their environment, here is a non-exhaustive list of examples:

- Trichobothrias are sensitive to movement in the air and help them to identify things such as a fly in flight

- Bristles act as sensors for vibrations in their nets, which is very useful when an insect has been trapped

- Other hairs function as laboratories that will analyse the ambient molecules, they are proper chemoreceptors.

Surprising as this may seem, it is not inconsistent to say that their hairs transmit more information to spiders than their eyes, even though most of them have 8.

Spiders are predators of rare efficiency

Why do spiders molt?

Because, unlike humans, for example, they have no 'internal skeleton", but an outside one, which is called an exoskeleton. This means that as they grow, they find themselves cramped in a hard cuticle which can not stretch. The only solution is to shed the old skin regularly for a new one, this operation is called molting. For most spider species, this happens a dozen times during their lives.

How does molting take place? When its exoskeleton becomes too small, the spider finds a safe place and makes it "crack". It then sheds its old skin with varying degrees of difficulty and taking advantage of the lack of stress, it increases in volume. The new skin will harden quickly, but during this time, it is particularly vulnerable to predators.

It sheds its old skin, which experts call "exuviae" and is often confused with a dead spider.

What is autotomy?

This is the impressive ability that spiders have to cut off a member in case of necessity! This amputation does not occur in just any way but so as not to endanger its life. In addition, it can regenerate the lost limb at its next molt.

How do spiders reproduce?

Most of the time, it's a tragic story for the male which will not survive. It will first produce sperm that is ejaculated onto a web that has been specially woven for this purpose. Then it transfers and stores it in bulbs (Called copulatory bulbs) located at the end of its pedipalps. The male is now ready to fertilise a female, but he must find her, to do this, pheromones will guide him as surely as a light in the night.

Pheromones are chemical substances produced by the body of most species, which are used to attract partners for the purpose of reproduction. The organs that allow spiders to receive and identify these chemical messages are located at the end of their legs.

Once the male has found the female, after a mating ritual specific to their species, they will mate. This is the introduction of the male copulatory bulbs into the female reproductive tract. Note that the shape of their respective sexual organs is unique to each species and prohibits reproduction between different species.

The end of copulation means death or at least a shortened life cycle for the male, who will either be devoured by the female, or die. For the female, the reproductive cycle is just beginning and depending on the species, she will lay eggs and abandon them (they are wrapped in a cocoon of silk), others keep them on their webs or even on themselves.

Spiders are oviparous, the number of eggs varies greatly from one species to another (from one to thousands).

Spiders are carnivorous predators that eat the prey they hunt in many ways. According to where spiders live, their diet is very wide, ranging from insects such as flies, mosquitoes, wasps, grasshoppers, butterflies and cockroaches, etc., to lizards or mice and tadpoles, frogs and even birds.

But spiders that cannot chew can only absorb liquids, so they must liquefy their prey by injecting venom into them (which contains digestive enzymes) because arachnids do not have a digestion process within their bodies (as with humans, for example) but externally (specialists call this process "lysis”).

It is important to note that unlike other mosquitoes and ticks, spiders do not feed on blood and are therefore not attracted to humans, which they consider, on the contrary, to be dangerous.

Are spiders useful?

In conjunction with the previous paragraph, it is no exaggeration to say that spiders are irreplaceable regulators, for example they get rid of insects, including mosquitoes. In this regard, they predate on insect pests, which should encourage us to treat them more leniently.

What is the geographical distribution of spiders? 

There are spiders all over the surface of the planet, with the exception of frozen regions, the highest mountains and salt water because although it may seem unbelievable, there are even spiders that live in water!

For example, take the Argyroneta, which weaves a bell-shaped web and attaches it to aquatic plants and fills them with air, making trips to and from the surface. Located in a submarine shelter, she can then hunt all kinds of prey.

How many species of spiders are there?

Approximately 40,000, you can find them by clicking here (http://research.amnh.org/iz/spiders/catalog/INTRO3.html), the worldwide catalogue of spiders established by Norman I. Platnick from the American Museum of Natural History.

This scientific site - in English – has a wealth of information on spiders, ranging from ‘Abacoproeces’ to ‘Zyngoonops’.

Wasp Spider (Argiope bruennichi)

Are spiders dangerous?

Few spiders are dangerous to humans, firstly because, as we have seen, they avoid contact and most are too small to bite or even inject enough venom.

However, the bad reputation of black widows, brown recluse spiders and tarantulas is not overrated, because they represent a real danger to humans. The black widow and brown recluse because of their venom and tarantulas, because they rub the bristles on their abdomen and eject them when they feel attacked, which can cause severe allergic reactions.

Spider silk

The ability of spiders to produce silk is a marvel of evolution that deserves a whole CyberDodo casefile. The silk glands (sericteria) are located in the abdomen (Opthisoma), producing the silk which remains in liquid form when it is in the body of the spider.

The silk will come out of holes (usually 6 in number) located under the abdomen, which are called spinnerets. Upon contact with the air, the silk will solidify and the spider will be able to use it. Silk? It would be more correct to describe them as silks, because spiders are capable of producing several different types of silk, depending on the intended use.

For example, a very strong silk, which will support it as it spins its web and then another very sticky one with which it will weave the thread, etc. Note that when it is the same size, spider silk is stronger than steel.

The qualities of strength, lightness and elasticity of spider silk have been researched a great deal in order to produce it industrially for uses as diverse as fishing line or tennis racquet strings. The military is also interested in using it to create bulletproof vests.

This strong interest in this extraordinary silk has even led to research that may surprise the defenders of the environment. The cells of the spider silk glands and those of the mammary glands of goats are similar; goats have been manipulated genetically in Canada and the United States to make them produce fibroin (which is the basic protein of spider thread).

Have spiders completed their evolution? 

This question would probably shock the famous English naturalist Charles Darwin (1809-1882), author of "The Origin of Species”, which laid the foundations of evolutionary theory, yet the history of spiders enables us to ask this question.

The answer is obviously "no" because it is known, thanks to Charles Darwin, that natural selection is continuously at work and that all species are constantly under pressure from their environment so that the most adapted individuals survive and transmit their genes to the next generations.

So why ask? Because spider fossils (Plectreuridae), as old as 150 to 200 million years, were found in China and their exceptional state of preservation showed that their descendants of today are almost identical to them!

To see the cartoon on spiders, click here

To see the spider game, click here

To do the quiz, click here

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