Spiders inhabit almost all ecosystems – they have been recorded on the Arctic and Antarctic, in deserts, caves, lakes and even at the altitude of 7 000 m. They are primarily ground dwelling creatures although there are also those that have started to inhabit water.

The spider’s body consists of two main regions, namely the cephalothorax (head-region) and the abdomen (stomach-region). These two regions are connected with a thin waist called the pedicle. The body surface is covered with chitin layer which also represents and exoskeleton.
Eight eyes (sometimes six), mouthparts, pedipalps and four pairs of legs are located on the cephalothorax. In front of the mouth there are tow chelicerae which are used to catch and kill the prey. The pedipalps are found laterally from the mouth. In females they are similar to the eight legs, but in males their structure is more complex, being used for copulation during the mating process. They are also used for taxonomical identification.

The four pairs of legs are placed laterally from the cephalothorax region. There are different groups of specialised hairs and spines on them and the longest among these are the sensory hairs (trichobothrium), providing the spiders with the capability to feel vibrations on the web or the ground. In addition to these tactile sensory organs, spiders also have scent sensory organs, which resemble to crack openings on the legs or some other parts of their body. Males use their scent sensory organs to find nearby females’ scent. In addition to these sensory organs, some spiders also have sound producing organs. These sounds are sometimes so loud that even a man can hear them.

In most cases the spider’s abdomen is oval in shaped, without traces of segmentation. It is mainly soft, diverse in shape, size and colour and sometimes has very distinct spines. On the ventral side (under-side) of the abdomen there is a small opening called the epigastric. This is where the spider’s genital opening can be found. The respiratory openings of the book-lungs or tracheas are placed laterally from the epigastric fold.

Spiders are well-known for their highly emphasised sexual dimorphism. In some species, like Nephila, the female is almost a thousand times larger than the male. All species show typical and specific behaviour during mating. Smaller males usually wait for a female to fall into a kind of cataleptic state so that they can fulfil their function and run away on time to avoid being eaten by a female.

Families of Lycosidae and Salticidae are known for their wedding dances. Males wave their pedipalps and drum their legs in a certain rhythm, moving constantly from side to side, or in a forward-backward motion. The Pisaura mirabilis males bring “wedding gifts” to their chosen female, a fly wrapped in the web, while males of the Xisticus gulosus species spin silk around the head and front legs of their brides in order to perform the act of mating.

All spiders lay eggs. These eggs are laid in silk sacks which are different in size and shape for different species. Some females carry the egg sacks with them until the young spiderlings hatch, while others keep them in the vicinity of the hunting webs. There are also those species that take no care of their eggs at all. The spiderlings stay in their silk sacks until their first moult (shedding of its skin in order to grow).

Spiders are best known for their web spinning capability. The spinnerets or silk producing glands can be found on the ventral (under) side of abdomen, closer to the posterior part of the body. Using their hind legs spiders extrude the web silk from these spinnerets. They use this silk to create different types of webs: hunting webs, dwelling webs, different shelters and cocoons for their eggs.

Spiders are predators and they feed on other organisms. While some species spin webs to catch their prey, other species attack their victims by means of stalking and jumping. Once the prey is caught, spiders use their chelicerae and venom to kill the victim. A spider’s venom can be either neurotoxic (acting on the nervous system) or cytotoxic (acting on the body tissue). General poisoning by spiders’ venom is called Aaneism, while more specifically poisoning by the venom of a button spider is called Latrodectism. Latrodectism creates a serious condition that can be fatal for little children or elderly people. It has been said that a button spider’s venom is fourteen times stronger than that of a rattlesnake (if measured drop by drop).

Spider related research is not directed towards the faunistic, taxonomical and toxicological areas only. Extensive research has also been made on spider silk. Scientists are currently researching spider silk as a possible replacement for Kevlar, the material used in bullet-proof vests, because of its natural strength and elasticity, while bridge builders have been known to study spider webs because of the webs' remarkable ability to absorb tension. And then moving off the silk topic there is also an interesting possibility of using spiders as bio-pesticides in greenhouse production of organic food.

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