|
General Information
Spiders are small, eight-legged creatures that are best known for spinning silk
webs. Spiders spin webs so they can catch insects for their food and even larger
and stronger insects cannot escape.
 All
spiders spin silk but some don't spin webs. Bolas spiders spin a single
line with a sticky end. Any insect near, gets trapped when the spider
swings the sticky line near them.
All spiders have
fangs and most kinds have poison glands. They use their fangs and poison
glands to capture their food. A spider's bite can kill insects and other
small animals. A few kinds of spiders are harmful to human beings. In North
America, six kinds of spiders harm people, they are - the Brown Recluse,
Sac, Black Widow, Brown Widow, Red-legged Widow and the Varied Widow. Four
of the Widow females are known to bite humans. The bites of these six
spiders often cause mild reactions. Usually a person irritates a spider
several times for it to bite you. In Australia, the most dangerous spider is
the Funnel-Web with the Red-back, a type of Black Widow spider, also being
dangerous. Spiders are helpful to people because they
eat harmful insects. They eat grasshoppers and locusts which destroy crops.
Spiders also eat flies and mosquitoes which carry diseases. Spiders feed
mostly on insects but some capture and eat tadpoles, small frogs, small fish
and mice. Most females are larger and stronger than the males and
occasionally they eat males. Spiders can live anywhere they can find food
like fields, woods, swamps, caves and deserts. One kind of spider spends
most of its life underwater. Another kind lives near the top of Mount
Everest, the world's highest mountain. Some live in houses, barns, and other
buildings. Others live on the outside of buildings, on walls, windscreens
and corners of doors and windows. The life span of
arachnids in temperate areas is a single season, therefore they rely on eggs
to perpetuate the species from year to year. In warm regions, certain groups
(some scorpions and tarantulas) appear to live more than a single year, in
fact some tarantulas in captivity have survived for as long as 20 years.
 There are more
than 30,000 kinds of spiders. Scientists believe there may be up to 50,000 to
100,000 kinds. Some are smaller than than the head of a pin but some are larger
than a person's hand. One kind of spider, a South American tarantula is measured
at 25 centimetres but that is with its legs extended. Most
people think spiders are insects but scientists classify spiders as
arachnids. Insects are different in a number of ways. Spiders have eight
legs but ants, bees, beetles and other insects have only six legs. Most
insects have wings or antennae which are feelers. Arachnids include daddy
long legs, scorpions, mites and ticks. Scientists
classify spiders as either true spiders or Tarantulas, according to certain
differences in their bodies such as the way their fangs point and move. In
addition, spiders can be grouped according to the way they live. Web
spinning spiders spin webs to catch insects. Others lie and wait for insects
to come.
Spiders' Bodies
Spiders may be all different shapes - short and fat, long
and thin, round, oblong, or flat and one even looks like a stick insect.
Their legs can be short and stubby, or long and thin. Spiders are most
commonly brown, grey, or black but some species have beautiful colours. Many
of these spiders are so small that their colours can be only seen with
a microscope.
A spider has no bones and 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: the
cephalothorax, which consists of the head joined to the thorax
(chest); and the abdomen. Each of these
sections has parts attached to it called appendages Connecting the the
cephalothorax and the abdomen is a thin waist called the
pedicel.
 Eyes.
A spider's eyes are on top and near the front of its head. Different species
have different numbers of eyes and the size and position also varies. Most
species have eight eyes, arranged in two rows of four each. Other kinds have
six, four, or two eyes. Some spiders have can see better than others.
Hunting spiders have good eyesight at short distances and their eyesight
allows them to form images of their prey and mates. Web-building spiders
have poor eyesight and 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. Below the spider's eyes is its mouth
opening. Spiders eat only liquids because they do not have chewing mouth
parts. Around the mouth are various appendages which form a short
"straw" through which the spider sucks the body fluid of its victim.
The spider can only eat some of the solid tissue of its prey by
predigesting it. The spider sprays digestive juices on the tissue and the
powerful juices dissolve the tissue. A large tarantula can reduce a
mouse to a small pile of hair and bones in about 36 hours by predigestion
and sucking.
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. At the end of each chelicera is 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 so that when
a spider bites an insect with its chelicerae, poison flows from the fangs
into the wound and paralyses or kills its prey.
 In
true spiders, the fangs point crosswise, and the poison glands extend back
into the cephalothorax. The fangs of tarantulas point straight down from the
head, and the poison glands are in the chelicerae. 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 parts. In
most kinds of spiders, the part closest to the body has a sharp plate with
jagged edges. The spider uses this plate to cut and crush its food. In adult
male spiders, the last part of each pedipalp has a reproductive organ.
Legs. A spider has four pairs of legs, which
are attached to its cephalothorax and each leg has seven segments. In most
kinds of spiders, the tip of the last segment has two or three claws.
Surrounding the claws is a pad of hairs called the scopula. The scopula
sticks to smooth surfaces and helps the spider walk on ceilings and walls.
Sensitive bristles that serve as organs of touch and perhaps organs of smell
also cover each leg. Some bristles pick up vibrations from the ground or
air, or the spider's leg while 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
so it is the pressure of the blood in their bodies that 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 may have four or two.
The tip of a spinneret is called the spinning field and the surface of each
spinning field is covered by as many as a hundred spinning tubes. Liquid
silk flows through these tubes from silk glands in the spider's abdomen to
the outside of its body and the silk then hardens into a thread.
Respiratory system. Spiders as a group have two
kinds of breathing organs - tracheae and
book lungs. Tracheae
are found in almost all kinds of true spiders and they are small tubes which
carry air directly to the body tissues. In front of the spinnerets in
most kinds of true spiders is an opening called the
spiracle and air enters the tubes through these openings.
Book lungs are in cavities in the spider's
abdomen and 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 colour. The heart,
is a long, slender tube in the abdomen, and 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 particles 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.
Because spiders can store food in the caeca, they can go for long periods of
time without eating.
Nervous system. In the cephalothorax is
the central nervous system including the brain, which is connected to a
large group of nerve cells called the ganglion.
Nerve fibres from the brain and ganglion run throughout a spider's body. The
nerve fibres 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 fibres to control the activities of the body.
 The
spider's silk
Making 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 fibre
known.
The spinnerets, which spin the silk, work like the fingers of a hand. A
spider can stretch out each spinneret, pull it back in, and even squeeze
them all together. A spider can use different spinnerets to 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 spinning field of 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 called a hackled band. 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 sometimes called the spider's "lifeline"
because the animal 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 discs.
They use the attachment discs to anchor their draglines and webs to various
surfaces.
Many kinds of spiders build silk nests as their homes. Some spiders line a
folded leaf with silk to make a nest. Others dig burrows in the ground and
line them with silk. Still other spiders build nests in the centre 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.
Types of Spiders
Hunting spiders
Hunting spiders creep up on their prey or lie in wait and pounce on it. Some
kinds of hunters, including jumping spiders and wolf spiders, have large
eyes and can see their prey from a distance. But other hunters, such as
water spiders, tarantulas, and crab spiders, have small eyes. 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. These spiders are all hunting spiders:
 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 colourful of all spiders. Many thick, coloured
hairs cover their bodies. Most male jumping spiders have bunches of brightly
coloured hairs on their first pair of legs.
Water spiders are the only spiders that live
most of their life underwater. The water 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. 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.
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 the water
without sinking. These spiders 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.
 Crab
spiders have short, wide bodies and look like small crabs. They can
walk backwards and sideways as easily as crabs do. Some brightly coloured
crab spiders hide in flowers and capture bees and butterflies. A few kinds
of crab spiders can disguise themselves by changing the colour of their
bodies to match the colour of the flower blossom.
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
wolf spiders make their homes near water and resemble fisher spiders in
appearance and habits. Others live in burrows, or spin funnel-shaped webs.
Web-spinning spiders
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. These spiders are all
web-spinning spiders:
Tangled-web weavers spin a web that consists of
a jumble of threads attached to a support, such as the corner of a ceiling.
 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 5
centimetres 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 and the Australian redback
spider are both comb-footed spiders.
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 and serves as the spider's hiding place. The top part of the
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.
Dwarf spiders, which are less than 1.3
millimetres long, spin small, square sheet webs near rivers and lakes.
Whip or tailed spiders live in Southeast Asia
and Australia. They have long, thin, tubelike bodies, 2 to 4 centimetres
long. At night the whip spider lets out a few long, thin strands of silk. It
then waits for its prey--mainly smaller spiders--to use these silklines as
"guide ropes." When the unsuspecting small spider climbs up such a rope the
whip spider snares it by wrapping it in a broad band of silk.
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 centre 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 centre of the web. Others
attach a signal thread to the centre of the web. The spider hides in its
nest near the web, and holds on to the signal thread. When an insect lands
in the web, the thread vibrates. The spider darts out and captures the
insect. Many orb weavers spin a new web every night. It takes them about an
hour. Such spiders often eat their old webs to conserve silk. Other orb
weavers repair or replace any damaged parts of their webs.
 Bolus
or angling spiders are classed as orb weavers, but they catch flying
insects by swinging a silk line with a sticky globule at one end. Some bolus
spiders are thought to give off a scent that attracts male moths.
Angling spiders have large, cream-coloured
bodies with pink, yellow, and brown markings. The
magnificent spider of Australia is a type of bolus spider.
The life of a spider
Each species of spider lives a different life. Many kinds of spiders live
for only about a year. Large wolf spiders live several years and some female
tarantulas have lived for up to 20 years in captivity. Spiders become adults
at different times of the year. Some mature in the autumn, and then mate and
die during the winter. Others live through the winter, mate in the spring,
and then die.
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 that identify themselves and attract the females. The
male of some species vibrates the threads of the female's web. Some male
hunting spiders wave their legs and bodies in an unusual courtship dance.
Male jumping spiders use the coloured hairs on their legs to signal females.
Male nursery web spiders present 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. Females can continue to lay eggs for
many months after mating because of the stored sperm.
 Eggs.
The number of eggs that a spider lays at one time varies with the
size of the animal. An average sized female lays about 100 eggs but 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 and then carries the
spiderlings on her back after they have hatched.
Spiderlings hatch inside the egg sac and remain there until warm weather
arrives. If the eggs are laid in autumn, the spiderlings stay quietly inside
their egg sac until spring. After leaving the egg sac, the spiderlings
immediately begin spinning draglines.
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 travelling is called ballooning. A spider may travel a
great distance by ballooning. Sailors more than 300 kilometres from land
have seen ballooning spiders.
Spiderlings moult (shed their outer skin) several times while they are
growing. A new, larger skin replaces the skin that has grown too tight. Most
kinds of spiders moult from five to nine times before they reach adulthood.
Tarantulas moult more than 20 times.
Spiders have many enemies including snakes, frogs, toads, lizards, birds,
fish, and other animals that also eat insects. Even some insects eat spiders
like the wasp which is one of the spider's worst enemies. One group of
spiders called pirate spiders eats nothing but other spiders.
Researched by Stacey (reference source "World Book Encyclopaedia")
Information
and pictures were taken from children's projects and where credited to that
child does not claim to be original information. Where possible, permission
to reproduce has been sought. Any infringement of copyright is purely
unintentional.
Click here to
return to the Other Spider's Home Page
|
