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All spiders spin silk, but some kinds of spiders do not make webs. The bolas spider, for example, spins a single line of silk with a drop of sticky silk at the end. When an insect flies near, this spider swings the line at it and traps the insect on the sticky ball.
All spiders have fangs, and most kinds of spiders have poison glands. Spiders use their fangs and poison glands to capture animals for food. A spider's bite can kill insects and other small animals. However, only a few kinds of spiders are harmful to human beings. In North America, six kinds of spiders have bites that can harm people. These are the brown recluse spider, the lynx spider, the black widow, the brown widow, the red widow, and the varied widow. Of the four widow spiders, only the females are known to bite humans. The bites of these six spiders often cause only mild reactions in people. Usually, a person must seriously annoy a spider before it will bite.
Spiders are helpful to people because they eat harmful insects. Spiders eat grasshoppers and locusts, which destroy crops, and flies and mosquitoes, which carry diseases. Although spiders feed mostly on insects, some spiders capture and eat tadpoles, small frogs, small fish, and mice. Spiders even eat each other. Most female spiders are larger and stronger than male spiders, and occasionally eat the males.
Spiders live anywhere they can find food. They can be seen in fields, woods, swamps, caves, and deserts. One kind of spider spends most of its life under water. Another kind lives near the top of Mount Everest, the world's highest mountain. Some spiders live in houses, barns, or other buildings. Others live on the outside of buildings--on walls, on window screens, or in the corners of doors and windows.
There are more than 30,000 known kinds of spiders, but scientists believe there may be as many as 50,000 to 100,000 kinds. Some kinds are smaller than the head of a pin. Others are as large as a person's hand. One spider, a South American tarantula, measured 10 inches (25 centimeters) long with its legs extended.
Many people think spiders are insects. However, scientists classify spiders as arachnids, which differ from insects in a number of ways. Spiders have eight legs. Ants, bees, beetles, and other insects have only six legs. In addition, most insects have wings and antennae (feelers), but spiders do not. Other arachnids include daddy longlegs, scorpions, and ticks. See ARACHNID.
Scientists classify spiders as either true spiders or tarantulas according to certain differences in their bodies, such as the way the fangs point and move. In addition, spiders can be grouped according to their way of life. Web-spinning spiders spin webs to trap insects. Hunting spiders run after insects or lie in wait for them. For more information on the scientific classification of spiders, see the table Common kinds of spiders with this article.
The spider's body
Spiders may be short and fat, long and thin, round, oblong, or flat. Their legs are short and stubby, or long and thin. Most spiders are brown, gray, or black. But some are as beautifully colored as the loveliest butterflies. Many of these spiders are so small that their colors can be seen only with a microscope.
A spider has no bones. Its tough skin serves as a protective outer skeleton. Hairs, humps, and spines (bristles of skin) cover the bodies of most spiders.
A spider's body has two main sections: (1) the cephalothorax, which consists of the head joined to the thorax (chest); and (2) the abdomen. Each of these sections has appendages (attached parts). A thin waist called the pedicel connects the cephalothorax and the abdomen.
Eyes. A spider's eyes are on top and near the front of its head. The size, number, and position of the eyes vary among different species. Most species have eight eyes, arranged in two rows of four each. Other kinds have six, four, or two eyes. Some spiders have better vision than others. For example, hunting spiders have good eyesight at short distances. Their eyesight enables them to form images of their prey and mates. Web-building spiders have poor eyesight. Their eyes are used for detecting changes in light. Some species of spiders that live in caves or other dark places have no eyes at all.
Mouth. A spider's mouth opening is below its eyes. Spiders do not have chewing mouth parts, and they eat only liquids. Various appendages around the mouth opening form a short "straw" through which the spider sucks the body fluid of its victim.
The spider can eat some of the solid tissue of its prey by predigesting it. To do this, the spider sprays digestive juices on the tissue. The powerful juices dissolve the tissue. By predigestion and sucking, a large tarantula can reduce a mouse to a small pile of hair and bones in about 36 hours.
Chelicerae are a pair of appendages that the spider uses to seize and kill its prey. The chelicerae are above the mouth opening and just below the spider's eyes. Each chelicera ends in a hard, hollow, pointed claw, and these claws are the spider's fangs. An opening in the tip of the fang connects with the poison glands. When a spider stabs an insect with its chelicerae, poison flows into the wound and paralyzes or kills the victim.
The fangs of tarantulas point straight down from the head, and the poison glands are in the chelicerae. In true spiders, the fangs point crosswise, and the poison glands extend back into the cephalothorax.
Spiders also crush their prey with their chelicerae. Some species use their chelicerae to dig burrows in the ground as nests.
Pedipalpi are a pair of appendages that look like small legs. One pedipalp is attached to each side of the spider's mouth, and they form the sides of the mouth. Each pedipalp has six segments (parts). In most kinds of spiders, the segment closest to the body bears a sharp plate with jagged edges. The spider uses this plate to cut and crush its food. In adult male spiders, the last segment of each pedipalp bears a reproductive organ.
Legs. A spider has four pairs of legs, which are attached to its cephalothorax. Each leg has seven segments. In most kinds of spiders, the tip of the last segment has two or three claws. A pad of hairs called a scopula may surround the claws. The scopula sticks to smooth surfaces and helps the spider walk on ceilings and walls. Each leg is also covered with sensitive bristles that serve as organs of touch and perhaps organs of smell. Some bristles pick up vibrations from the ground or air, or the spider's leg. Others detect chemicals in the environment.
When a spider walks, the first and third leg on one side of its body move with the second and fourth leg on the other side. Muscles in the legs make the legs bend at the joints. But spiders have no muscles to extend their legs. The pressure of the blood in their bodies makes their legs extend. If a spider's body does not contain enough fluids, its blood pressure drops. The legs draw up under the body, and the animal cannot walk.
Spinnerets are short, fingerlike organs with which the spider spins silk. They are attached to the rear of the abdomen. Most kinds of spiders have six spinnerets, but some have four or two. The tip of a spinneret is called the spinning field. The surface of each spinning field is covered by as many as a hundred spinning tubes. Through these tubes, liquid silk flows from silk glands in the spider's abdomen to the outside of its body. The silk then hardens into a thread.
Respiratory system. Spiders have two kinds of breathing organs--tracheae and book lungs. Tracheae, found in almost all kinds of true spiders, are small tubes which carry air to the body tissues. Air enters the tubes through one or, rarely, two spiracles. A spiracle is an opening in front of the spinnerets in most true spiders.
Book lungs are in cavities in the spider's abdomen. Air enters the cavities through a tiny slit on each side and near the front of the abdomen. Each lung consists of 15 or more thin, flat folds of tissue arranged like the pages of a book. The sheets of tissue contain many blood vessels. As air circulates between the sheets, oxygen passes into the blood. Tarantulas have two pairs of book lungs. Most true spiders have one pair.
Circulatory system. The blood of spiders contains many pale blood cells and is slightly bluish in color. The heart, a long, slender tube in the abdomen, pumps the blood to all parts of the body. The blood returns to the heart through open passages instead of closed tubes, such as those of the human body. If the spider's skin is broken, the blood quickly drains from its body.
Digestive system. A digestive tube extends the length of the spider's body. In the cephalothorax, the tube is larger and forms a sucking stomach. When the stomach's powerful muscles contract, the size of the stomach increases. This causes a strong sucking action that pulls the food through the stomach into the intestine. Juices in the digestive tube break the liquid food into molecules small enough to pass through the walls of the intestine into the blood. The food is then distributed to all parts of the body. Food is also pulled through the stomach into a fingerlike cavity called the caeca. The ability to store food in the caeca enables spiders to go for long periods of time, over a year in some cases, without eating.
Nervous system. The central nervous system of a spider is in the cephalothorax. It includes the brain, which is connected to a large group of nerve cells called the ganglion. Nerve fibers from the brain and ganglion run throughout a spider's body. The nerve fibers carry information to the brain from sense organs on the head, legs, and other parts of the body. The brain can also send signals through the nerve fibers to control the activities of the body.
The spider's silk
How spiders make silk. Spider silk is made up of protein and forms in the spider's silk glands. As a group, spiders have seven kinds of silk glands. However, no species of spider has all seven kinds. All spiders have at least three kinds of silk glands, and most species have five. Each kind of gland produces a different type of silk. Some silk glands produce a liquid silk that becomes dry outside the body. Other glands produce a sticky silk that stays sticky. Spider silk cannot be dissolved in water and is the strongest natural fiber known.
The spinnerets, which spin the silk, work somewhat like the fingers of a hand. A spider can stretch out each spinneret, pull it back in, and even squeeze them all together. Using different spinnerets, a spider can combine silk from different silk glands and produce a very thin thread or a thick, wide band.
Some spiders also can make a sticky thread that looks like a beaded necklace. To do this, the spider pulls out a dry thread that is heavily coated with sticky silk. It then lets go of the thread with a snap. This action causes the liquid silk to form a series of tiny beads along the thread. A spider uses beaded threads in its web to help trap jumping or flying insects.
Some kinds of spiders have another spinning organ called the cribellum. It is an oval plate that lies almost flat against the abdomen, in front of the spinnerets. Hundreds of spinning tubes cover the cribellum. These tubes produce extremely thin threads of sticky silk.
Spiders with a cribellum also have a special row of curved hairs called a calamistrum on their hind legs. Spiders use the calamistrum to comb together dry silk from the spinnerets and sticky silk from the cribellum. This combination of threads forms a flat, ribbonlike silk structure consisting of many microscopic fibers. This structure, called a hackled band, is highly effective in catching and restraining insects and other small prey. Spiders use hackled bands in their webs, along with the other silk that they spin.
How spiders use silk. Spiders, including those that do not spin webs, depend on silk in so many ways that they could not live without it. Wherever a spider goes, it spins a silk thread behind itself. This thread is called a dragline. The dragline is also called a "lifeline" because the spider often uses it to escape from enemies.
If danger threatens a spider in its web, it can drop from the web on its dragline and hide in the grass. Or the spider can simply hang in the air until the danger has passed. Then it climbs back up the dragline into its web. Hunting spiders use their draglines to swing down to the ground from high places.
Spiders also use silk to spin tiny masses of sticky threads called attachment disks. They use the attachment disks to anchor their draglines and webs to various surfaces.
Each kind of spider builds a different type of silk nest as its home. Some spiders line a folded leaf with silk to make a nest. Others dig burrows in the ground and line them with silk. Still others build nests in the center of their webs.
Many web-spinning spiders spin sticky bands or wide sheets of silk while capturing their prey. The orb weavers wrap their victims in sheets like mummies so they cannot escape.
The female spider of most species encloses her eggs in an egg sac. This sac is a bag made of a special kind of silk.
Hunting spiders creep up on their prey or lie in wait and pounce on it. Most kinds of hunters have large eyes and can see their prey from a distance. Tarantulas have poor vision and use a system of silk lines radiating away from their nests to locate passing prey. The powerful chelicerae of hunting spiders help them overpower their victims. Some hunting spiders spin simple webs that stretch out along the ground and stop insects. These spiders are grouped as hunters because they run after the insects that land in their webs.
Jumping spiders creep up and pounce on their prey. These spiders have short legs, but they can jump more than 40 times the length of their bodies. Jumping spiders are the most colorful of all spiders. Many thick, colored hairs cover their bodies. Most male jumping spiders have bunches of brightly colored hairs on their first pair of legs.
Water spiders are the only spiders that live most of their life underwater. This spider breathes underwater from air bubbles that it holds close to its body. Its underwater nest is a silk web shaped like a small bell. The spider fills the web with air bubbles, which gradually push all the water out of the bell. The animal can live on this air for several months. Water spiders are found only in Europe and parts of Asia.
Tarantulas are the world's largest spiders. The biggest ones live in the South American jungles. Great numbers of tarantulas also are found in the Southwestern United States. Many kinds of tarantulas dig burrows as nests. The trap-door spider covers the entrance to its burrow with a lid (see TRAP-DOOR SPIDER). A California tarantula builds a turret (small tower) of grass and twigs at the entrance to its burrow. This spider then sits on the tower and watches for insects moving in the nearby grass. A few kinds of tarantulas live in trees. See TARANTULA.
Fisher spiders live near water and hunt water insects, small fish, and tadpoles. These spiders have large bodies and long, thin legs. But because of their light weight, they can walk on water without sinking. They also can dive underwater for short periods of time. Some fisher spiders are called nursery-web weavers because the female builds a special web for her young.
Wolf spiders are very common and are excellent hunters. Many kinds have large, hairy bodies, and run swiftly in search of food. Others look and act like other types of spiders. For example, some live near water and resemble fisher spiders in appearance and habits. Others live in burrows, or spin funnel-shaped webs.
Web-spinning spiders, like hunting spiders, live in caves, in grass or shrubs, or in trees. They cannot catch food by hunting because of their poor vision. Instead, they spin webs to trap insects. A web-spinning spider does not become caught in its own web. When walking across the web, it grasps the silk lines with a special hooked claw on each foot.
Tangled-web weavers spin the simplest type of web. It consists of a jumble of threads attached to a support, such as the corner of a ceiling. Cobwebs are old tangled webs that have collected dust and dirt.
The cellar spiders spin tangled webs in dark, empty parts of buildings. One cellar spider that looks like a daddy longlegs has thin legs more than 2 inches (5 centimeters) long.
The comb-footed spiders spin a tangled web with a tightly woven sheet of silk in the middle. The sheet serves as an insect trap and as the spider's hideout. These spiders get their name from the comb of hairs on their fourth pair of legs. They use the comb to throw liquid silk over an insect and trap it. The black widow is a comb-footed spider (see BLACK WIDOW).
Some spiders spin a tangled web containing a hackled band of dry and sticky silk. The ogre-faced stick spider spins a web that is made up largely of hackled bands. The web is only about as large as a postage stamp. This spider spins a structure of dry silk to hold the sticky web in place. The spider hangs upside down from the dry silk. It holds the sticky web with its four front legs. When an insect crawls or flies near, the spider stretches the sticky web to several times its normal size and sweeps it over the insect.
Funnel-web spiders live in large webs that they spin in tall grass or under rocks or logs. The bottom of the web is shaped like a funnel. This funnel serves as the spider's hiding place. The top part of the spider's web forms a large sheet of silk spread out over grass or soil. When an insect lands on the sheet, the spider runs out of the funnel and pounces on the victim.
Sheet-web weavers weave flat sheets of silk between blades of grass or branches of shrubs or trees. These spiders also spin a net of crisscrossed threads above the sheet web. When a flying insect hits the net, it bounces into the sheet web. Often, an insect will fly directly into the sheet web. The spider, which hangs beneath the web, quickly runs to the insect and pulls it through the webbing. Sheet webs last a long time because the spider repairs any damaged parts.
Orb weavers build the most beautiful and complicated of all webs. They weave their round webs in open areas, often between tree branches or flower stems. Threads of dry silk extend from an orb web's center like the spokes of a wheel. Coiling lines of sticky silk connect the spokes, and serve as an insect trap.
Some orb weavers lie in wait for their prey in the center of the web. Others attach a trap line to the center of the web. The spider hides in its nest near the web, and holds on to the trap line. When an insect lands in the web, the line vibrates. The spider darts out and captures the insect. Many orb weavers spin a new web every night. It takes about an hour. Such spiders often eat their old webs to conserve silk and to make use of the nutrients of any tiny insects caught in the web. Other orb weavers repair or replace damaged parts of their webs.
The life of a spider
Each species of spider has a different life story. Many kinds of spiders live only about a year. Large wolf spiders live several years. Some female tarantulas have lived up to 20 years in captivity. Spiders become adults at different times of the year. Some mature in the fall, and then mate and die during the winter. Others live through the winter, mate in the spring, and then die.
Except during mating, most spiders are loners. In some species of hackled-band orb weavers, individual spiders will interconnect their webs. But such social behavior is rare among spiders.
Courtship and mating. As soon as a male spider matures, it seeks a mate. The female spider may mistake the male for prey and eat him. But most male spiders perform courtship activities to identify themselves and attract females. The male of some species vibrates the female's web. Some male hunting spiders wave their legs and bodies in a courtship dance. Male jumping spiders use the colored hairs on their legs to signal females. In some species of nursery web spiders, the male presents the female with a captured fly before mating.
Before mating, the male spider spins a silk platform called a sperm web. He deposits a drop of sperm from his abdomen onto the platform. Then he fills each of his pedipalpi with sperm. He uses the pedipalpi to transfer the sperm to females during mating. After mating, the female stores the sperm in her body. When she lays her eggs, several weeks or even months later, the eggs are fertilized by the sperm. Usually, the female does not eat the male after mating as is commonly believed.
Eggs. The number of eggs that a spider lays at one time varies with the size of the animal. A female of average size lays about 100 eggs. Some of the largest spiders lay more than 2,000 eggs.
In most species, the mother spider encloses the eggs in a silken egg sac. The sac of each species differs in size and shape. In many species, the mother dies soon after making the egg sac. In other species, she stays with the eggs until they hatch. Some spiders hang the sac in a web. Others attach the sac to leaves or plants. Still others carry it with them. The female wolf spider attaches the sac to her spinnerets, and drags it behind her.
Spiderlings hatch inside the egg sac. They do not leave the sac immediately because they are not yet able to spin silk. After molting (shedding their outer skin) once within the egg sac, the spiderlings are developed enough to leave. But they remain in the sac until warm weather arrives. If the eggs are laid in autumn, the spiderlings stay inside their egg sac until spring. After leaving the sac, most spiderlings begin spinning draglines. In a few species, the spiderlings remain for a time in the mother's web and share the food she captures.
Many spiderlings travel to other areas. To do this, a spiderling climbs to the top of a fence post or some other tall object and tilts its spinnerets up into the air. The moving air pulls silk threads out of the spinnerets. Then the wind catches the threads and carries the spiderling into the air. This unusual way of traveling is called ballooning. A spider may travel a great distance by ballooning. Sailors more than 200 miles (320 kilometers) from land have seen ballooning spiders.
Spiderlings molt several times. A new, larger skin replaces the skin that has grown too tight. Most kinds of spiders molt from five to nine times before they reach adulthood. Tarantulas molt more than 20 times.
Enemies of spiders include snakes, frogs, toads, lizards, birds, fish, and other animals that also eat insects. Even some insects eat spiders. The wasp is one of the spider's worst enemies (see WASP [Food]). Pirate spiders eat only other spiders.
It is quite obvious to me that you are copying text from other digital sources (online website?!) Due to copyright issues i do not suggest to keep copy/pasting vast text data. The forum is meant to share OWN opinions and knowledge, and there is nothing wrong that ocassionally you support your opinions/ideas/knowledge from external sources, BUT there is no need to start a new topic and (eg Spiders in this case) and copy the text from an encyclopaedia or other external sources and paste it in the post unless specifically requested by a member.
In such case, giving reference to the external source is recommended. Hope you can understand the point.
As a thumb rule, the forum is sharing of OWN stuff!
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http://www.google.co.uk/search?sourceid ... eir+bodies
Of course no one knows WHO wrote the original articles, so
- Posts: 34
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You tend to jump to conclusions.
1) Spiders are certainly not a vague subject to write about.
2) I thought I followed is from a prompt from
Cocholin, one of this forum's members.
3) It was him that was writing about WOLF SPIDERS, before my post.
4) Just to put the record straight, David Cilia happens to be
one of the my extended relatives.
5) I have always had great regards for David. He was always
a great lover of nature and also a collector of stones from different parts of the world.
6) It would be intresting to know , whether he has the
pendant with a shark's tooth that we got for him about
twenty years ago.
Thanks for you the prev posts and was interesting to see how small the word is.
Ref. to the spider post, than it would have more appropriate to write info specifically on "Wolf spiders" as a reply on the Conch's topic, the same as you generously did for my Lichens post. What do you think? Please regard it just as comformity guidelines.