113 families, c. 46,000 species
Spiders (order Araneae) are air-breathing arthropods that have eight
legs and chelicerae with fangs that inject venom. They are the largest
order of arachnids and rank seventh in total species diversity among
all other orders of organisms. Spiders are found worldwide on every
continent except for Antarctica, and have become established in nearly
every habitat with the exceptions of air and sea colonization. As of
November 2015[update], at least 45,700 spider species, and 113
families have been recorded by taxonomists. However, there has been
dissension within the scientific community as to how all these
families should be classified, as evidenced by the over 20 different
classifications that have been proposed since 1900.
Anatomically, spiders differ from other arthropods in that the usual
body segments are fused into two tagmata, the cephalothorax and
abdomen, and joined by a small, cylindrical pedicel. Unlike insects,
spiders do not have antennae. In all except the most primitive group,
the Mesothelae, spiders have the most centralized nervous systems of
all arthropods, as all their ganglia are fused into one mass in the
cephalothorax. Unlike most arthropods, spiders have no extensor
muscles in their limbs and instead extend them by hydraulic pressure.
Their abdomens bear appendages that have been modified into spinnerets
that extrude silk from up to six types of glands.
Spider webs vary
widely in size, shape and the amount of sticky thread used. It now
appears that the spiral orb web may be one of the earliest forms, and
spiders that produce tangled cobwebs are more abundant and diverse
than orb-web spiders. Spider-like arachnids with silk-producing
spigots appeared in the
Devonian period about 386 million years
ago, but these animals apparently lacked spinnerets. True spiders have
been found in
Carboniferous rocks from 318 to 299 million
years ago, and are very similar to the most primitive surviving
suborder, the Mesothelae. The main groups of modern spiders,
Mygalomorphae and Araneomorphae, first appeared in the Triassic
period, before 200 million years ago.
A herbivorous species, Bagheera kiplingi, was described in 2008,
but all other known species are predators, mostly preying on insects
and on other spiders, although a few large species also take birds and
lizards. It is estimated that the world's 25 million tons of spiders
kill 400–800 million tons of prey per year. Spiders use a wide
range of strategies to capture prey: trapping it in sticky webs,
lassoing it with sticky bolas, mimicking the prey to avoid detection,
or running it down. Most detect prey mainly by sensing vibrations, but
the active hunters have acute vision, and hunters of the genus Portia
show signs of intelligence in their choice of tactics and ability to
develop new ones. Spiders' guts are too narrow to take solids, so they
liquefy their food by flooding it with digestive enzymes. They also
grind food with the bases of their pedipalps, as arachnids do not have
the mandibles that crustaceans and insects have.
To avoid being eaten by the females, which are typically much larger,
male spiders identify themselves to potential mates by a variety of
complex courtship rituals. Males of most species survive a few
matings, limited mainly by their short life spans. Females weave silk
egg-cases, each of which may contain hundreds of eggs. Females of many
species care for their young, for example by carrying them around or
by sharing food with them. A minority of species are social, building
communal webs that may house anywhere from a few to 50,000
individuals. Social behavior ranges from precarious toleration, as in
the widow spiders, to co-operative hunting and food-sharing. Although
most spiders live for at most two years, tarantulas and other
mygalomorph spiders can live up to 25 years in captivity.
While the venom of a few species is dangerous to humans, scientists
are now researching the use of spider venom in medicine and as
Spider silk provides a combination of
lightness, strength and elasticity that is superior to that of
synthetic materials, and spider silk genes have been inserted into
mammals and plants to see if these can be used as silk factories. As a
result of their wide range of behaviors, spiders have become common
symbols in art and mythology symbolizing various combinations of
patience, cruelty and creative powers. An abnormal fear of spiders is
1.1 Body plan
1.2 Circulation and respiration
1.3 Feeding, digestion and excretion
1.4 Central nervous system
1.5 Sense organs
1.5.2 Other senses
1.8 Reproduction and life cycle
2 Ecology and behavior
2.1 Non-predatory feeding
2.2 Methods of capturing prey
2.4 Social spiders
3 Web types
3.1 Orb webs
3.2 Tangleweb spiders (cobweb spiders)
3.3 Other types of webs
4.1 Fossil record
4.2 Family tree
6 Spiders and people
6.2 Benefits to humans
6.4 Spiders in symbolism and culture
7 See also
10 Further reading
11 External links
Palystes castaneus female
3: carapace of prosoma (cephalothorax)
4: opisthosoma (abdomen)
5: eyes – AL (anterior lateral)
AM (anterior median)
PL (posterior lateral)
PM (posterior median)
Nos 1 to 14 as for dorsal aspect
15: sternum of prosoma
16: pedicel (also called pedicle)
17: book lung sac
18: book lung stigma
19: epigastric fold
21: anterior spinneret
22: posterior spinneret
I, II, III, IV = Leg numbers from anterior to posterior
Spiders are chelicerates and therefore arthropods. As arthropods
they have: segmented bodies with jointed limbs, all covered in a
cuticle made of chitin and proteins; heads that are composed of
several segments that fuse during the development of the embryo.
Being chelicerates, their bodies consist of two tagmata, sets of
segments that serve similar functions: the foremost one, called the
cephalothorax or prosoma, is a complete fusion of the segments that in
an insect would form two separate tagmata, the head and thorax; the
rear tagma is called the abdomen or opisthosoma. In spiders, the
cephalothorax and abdomen are connected by a small cylindrical
section, the pedicel. The pattern of segment fusion that forms
chelicerates' heads is unique among arthropods, and what would
normally be the first head segment disappears at an early stage of
development, so that chelicerates lack the antennae typical of most
arthropods. In fact, chelicerates' only appendages ahead of the mouth
are a pair of chelicerae, and they lack anything that would function
directly as "jaws". The first appendages behind the mouth are
called pedipalps, and serve different functions within different
groups of chelicerates.
Spiders and scorpions are members of one chelicerate group, the
arachnids. Scorpions' chelicerae have three sections and are used
in feeding. Spiders' chelicerae have two sections and terminate in
fangs that are generally venomous, and fold away behind the upper
sections while not in use. The upper sections generally have thick
"beards" that filter solid lumps out of their food, as spiders can
take only liquid food. Scorpions' pedipalps generally form large
claws for capturing prey, while those of spiders are fairly small
appendages whose bases also act as an extension of the mouth; in
addition, those of male spiders have enlarged last sections used for
In spiders, the cephalothorax and abdomen are joined by a small,
cylindrical pedicel, which enables the abdomen to move independently
when producing silk. The upper surface of the cephalothorax is covered
by a single, convex carapace, while the underside is covered by two
rather flat plates. The abdomen is soft and egg-shaped. It shows no
sign of segmentation, except that the primitive Mesothelae, whose
living members are the Liphistiidae, have segmented plates on the
Circulation and respiration
Like other arthropods, spiders are coelomates in which the coelom is
reduced to small areas round the reproductive and excretory systems.
Its place is largely taken by a hemocoel, a cavity that runs most of
the length of the body and through which blood flows. The heart is a
tube in the upper part of the body, with a few ostia that act as
non-return valves allowing blood to enter the heart from the hemocoel
but prevent it from leaving before it reaches the front end.
However, in spiders, it occupies only the upper part of the abdomen,
and blood is discharged into the hemocoel by one artery that opens at
the rear end of the abdomen and by branching arteries that pass
through the pedicle and open into several parts of the cephalothorax.
Hence spiders have open circulatory systems. The blood of many
spiders that have book lungs contains the respiratory pigment
hemocyanin to make oxygen transport more efficient.
Spiders have developed several different respiratory anatomies, based
on book lungs, a tracheal system, or both.
Mygalomorph and Mesothelae
spiders have two pairs of book lungs filled with haemolymph, where
openings on the ventral surface of the abdomen allow air to enter and
diffuse oxygen. This is also the case for some basal araneomorph
spiders, like the family Hypochilidae, but the remaining members of
this group have just the anterior pair of book lungs intact while the
posterior pair of breathing organs are partly or fully modified into
tracheae, through which oxygen is diffused into the haemolymph or
directly to the tissue and organs. The trachea system has most
likely evolved in small ancestors to help resist desiccation. The
trachea were originally connected to the surroundings through a pair
of openings called spiracles, but in the majority of spiders this pair
of spiracles has fused into a single one in the middle, and moved
backwards close to the spinnerets. Spiders that have tracheae
generally have higher metabolic rates and better water
conservation. Spiders are ectotherms, so environmental
temperatures affect their activity.
Feeding, digestion and excretion
Cheiracanthium punctorium, displaying fangs
Uniquely among chelicerates, the final sections of spiders' chelicerae
are fangs, and the great majority of spiders can use them to inject
venom into prey from venom glands in the roots of the chelicerae.
Uloboridae and Holarchaeidae, and some Liphistiidae
spiders, have lost their venom glands, and kill their prey with silk
instead. Like most arachnids, including scorpions, spiders have
a narrow gut that can only cope with liquid food and spiders have two
sets of filters to keep solids out. They use one of two different
systems of external digestion. Some pump digestive enzymes from the
midgut into the prey and then suck the liquified tissues of the prey
into the gut, eventually leaving behind the empty husk of the prey.
Others grind the prey to pulp using the chelicerae and the bases of
the pedipalps, while flooding it with enzymes; in these species, the
chelicerae and the bases of the pedipalps form a preoral cavity that
holds the food they are processing.
The stomach in the cephalothorax acts as a pump that sends the food
deeper into the digestive system. The mid gut bears many digestive
ceca, compartments with no other exit, that extract nutrients from the
food; most are in the abdomen, which is dominated by the digestive
system, but a few are found in the cephalothorax.
Most spiders convert nitrogenous waste products into uric acid, which
can be excreted as a dry material.
Malphigian tubules ("little tubes")
extract these wastes from the blood in the hemocoel and dump them into
the cloacal chamber, from which they are expelled through the anus.
Production of uric acid and its removal via
Malphigian tubules are a
water-conserving feature that has evolved independently in several
arthropod lineages that can live far away from water, for example
the tubules of insects and arachnids develop from completely different
parts of the embryo. However, a few primitive spiders, the
Mesothelae and infra-order Mygalomorphae, retain the
ancestral arthropod nephridia ("little kidneys"), which use large
amounts of water to excrete nitrogenous waste products as ammonia.
Central nervous system
The basic arthropod central nervous system consists of a pair of nerve
cords running below the gut, with paired ganglia as local control
centers in all segments; a brain formed by fusion of the ganglia for
the head segments ahead of and behind the mouth, so that the esophagus
is encircled by this conglomeration of ganglia. Except for the
primitive Mesothelae, of which the
Liphistiidae are the sole surviving
family, spiders have the much more centralized nervous system that is
typical of arachnids: all the ganglia of all segments behind the
esophagus are fused, so that the cephalothorax is largely filled with
nervous tissue and there are no ganglia in the abdomen; in
the Mesothelae, the ganglia of the abdomen and the rear part of the
cephalothorax remain unfused.
Despite the relatively small central nervous system, some spiders
(like Portia) exhibit complex behaviour, including the ability to use
a trial-and-error approach.
This jumping spider's main ocelli (center pair) are very acute. The
outer pair are "secondary eyes" and there are other pairs of secondary
eyes on the sides and top of its head.
Spiders have primarily four pairs of eyes on the top-front area of the
cephalothorax, arranged in patterns that vary from one family to
another. The principal pair at the front are of the type called
pigment-cup ocelli ("little eyes"), which in most arthropods are only
capable of detecting the direction from which light is coming, using
the shadow cast by the walls of the cup. However, in spiders these
eyes are capable of forming images. The other pairs, called
secondary eyes, are thought to be derived from the compound eyes of
the ancestral chelicerates, but no longer have the separate facets
typical of compound eyes. Unlike the principal eyes, in many spiders
these secondary eyes detect light reflected from a reflective tapetum
lucidum, and wolf spiders can be spotted by torch light reflected from
the tapeta. On the other hand, jumping spiders' secondary eyes have no
Other differences between the principal and secondary eyes are that
the latter have rhabdomeres that point away from incoming light, just
like in vertebrates, while the arrangement is the opposite in the
former. The principal eyes are also the only ones with eye muscles,
allowing them to move the retina. Having no muscles, the secondary
eyes are immobile.
Some jumping spiders' visual acuity exceeds by a factor of ten that of
dragonflies, which have by far the best vision among insects; in fact
the human eye is only about five times sharper than a jumping
spider's. They achieve this by a telephoto-like series of lenses, a
four-layer retina and the ability to swivel their eyes and integrate
images from different stages in the scan. The downside is that the
scanning and integrating processes are relatively slow.
There are spiders with a reduced number of eyes, of these those with
six-eyes are the most numerous and are missing a pair of eyes on the
anterior median line, others species have four-eyes and some just
two. Cave dwelling species have no eyes, or possess vestigial eyes
incapable of sight.
As with other arthropods, spiders' cuticles would block out
information about the outside world, except that they are penetrated
by many sensors or connections from sensors to the nervous system. In
fact, spiders and other arthropods have modified their cuticles into
elaborate arrays of sensors. Various touch sensors, mostly bristles
called setae, respond to different levels of force, from strong
contact to very weak air currents. Chemical sensors provide
equivalents of taste and smell, often by means of setae. An adult
Araneus may have up to 1000 such chemosensitive setae, most on the
tarsi of the first pair of legs. Males have more chemosensitive hairs
on their pedipalps than females. They have been shown to be responsive
to sex pheromones produced by females, both contact and air-borne.
Spiders also have in the joints of their limbs slit sensillae that
detects force and vibrations. In web-building spiders, all these
mechanical and chemical sensors are more important than the eyes,
while the eyes are most important to spiders that hunt actively.
Like most arthropods, spiders lack balance and acceleration sensors
and rely on their eyes to tell them which way is up. Arthropods'
proprioceptors, sensors that report the force exerted by muscles and
the degree of bending in the body and joints, are well understood. On
the other hand, little is known about what other internal sensors
spiders or other arthropods may have.
Image of a spider leg: 1–coxa; 2–trochanter; 3–femur;
4–patella; 5–tibia; 6–metatarsus; 7–tarsus; 8–claws
Each of the eight legs of a spider consists of seven distinct parts.
The part closest to and attaching the leg to the cephalothorax is the
coxa; the next segment is the short trochanter that works as a hinge
for the following long segment, the femur; next is the spider's knee,
the patella, which acts as the hinge for the tibia; the metatarsus is
next, and it connects the tibia to the tarsus (which may be thought of
as a foot of sorts); the tarsus ends in a claw made up of either two
or three points, depending on the family to which the spider belongs.
Although all arthropods use muscles attached to the inside of the
exoskeleton to flex their limbs, spiders and a few other groups still
use hydraulic pressure to extend them, a system inherited from their
pre-arthropod ancestors. The only extensor muscles in spider legs
are located in the three hip joints (bordering the coxa and the
trochanter). As a result, a spider with a punctured cephalothorax
cannot extend its legs, and the legs of dead spiders curl up.
Spiders can generate pressures up to eight times their resting level
to extend their legs, and jumping spiders can jump up to 50 times
their own length by suddenly increasing the blood pressure in the
third or fourth pair of legs. Although larger spiders use
hydraulics to straighten their legs, unlike smaller jumping spiders
they depend on their flexor muscles to generate the propulsive force
for their jumps.
Most spiders that hunt actively, rather than relying on webs, have
dense tufts of fine hairs between the paired claws at the tips of
their legs. These tufts, known as scopulae, consist of bristles whose
ends are split into as many as 1,000 branches, and enable spiders with
scopulae to walk up vertical glass and upside down on ceilings. It
appears that scopulae get their grip from contact with extremely thin
layers of water on surfaces. Spiders, like most other arachnids,
keep at least four legs on the surface while walking or running.
An orb weaver producing silk from its spinnerets
The abdomen has no appendages except those that have been modified to
form one to four (usually three) pairs of short, movable spinnerets,
which emit silk. Each spinneret has many spigots, each of which is
connected to one silk gland. There are at least six types of silk
gland, each producing a different type of silk.
Silk is mainly composed of a protein very similar to that used in
insect silk. It is initially a liquid, and hardens not by exposure to
air but as a result of being drawn out, which changes the internal
structure of the protein. It is similar in tensile strength to
nylon and biological materials such as chitin, collagen and cellulose,
but is much more elastic. In other words, it can stretch much further
before breaking or losing shape.
Some spiders have a cribellum, a modified spinneret with up to 40,000
spigots, each of which produces a single very fine fiber. The fibers
are pulled out by the calamistrum, a comb-like set of bristles on the
jointed tip of the cribellum, and combined into a composite woolly
thread that is very effective in snagging the bristles of insects. The
earliest spiders had cribella, which produced the first silk capable
of capturing insects, before spiders developed silk coated with sticky
droplets. However, most modern groups of spiders have lost the
Tarantulas also have silk glands in their feet.
Even species that do not build webs to catch prey use silk in several
ways: as wrappers for sperm and for fertilized eggs; as a "safety
rope"; for nest-building; and as "parachutes" by the young of some
Reproduction and life cycle
Mating behaviour of Neriene radiata
The tiny male of the
Golden orb weaver
Golden orb weaver (Nephila clavipes) (near the
top of the leaf) is protected from the female by his producing the
right vibrations in the web, and may be too small to be worth eating.
Spiders reproduce sexually and fertilization is internal but indirect,
in other words the sperm is not inserted into the female's body by the
male's genitals but by an intermediate stage. Unlike many land-living
arthropods, male spiders do not produce ready-made spermatophores
(packages of sperm), but spin small sperm webs on to which they
ejaculate and then transfer the sperm to special syringe-like
structures, palpal bulbs or palpal organs, borne on the tips of the
pedipalps of mature males. When a male detects signs of a female
nearby he checks whether she is of the same species and whether she is
ready to mate; for example in species that produce webs or "safety
ropes", the male can identify the species and sex of these objects by
Spiders generally use elaborate courtship rituals to prevent the large
females from eating the small males before fertilization, except where
the male is so much smaller that he is not worth eating. In
web-weaving species, precise patterns of vibrations in the web are a
major part of the rituals, while patterns of touches on the female's
body are important in many spiders that hunt actively, and may
"hypnotize" the female. Gestures and dances by the male are important
for jumping spiders, which have excellent eyesight. If courtship is
successful, the male injects his sperm from the palpal bulbs into the
female's genital opening, known as the epigyne, on the underside of
her abdomen. Female's reproductive tracts vary from simple tubes to
systems that include seminal receptacles in which females store sperm
and release it when they are ready. Because the sperm is stored in
the epigyne, the eggs are not fertilized while inside the female, but
during oviposition when the stored sperm is released from its chamber.
The only one exception is a spider from Israel, Harpactea sadistica,
which has evolved traumatic insemination. In this species the male
will penetrate its pedipalps through the female's body wall and inject
his sperm directly into her ovaries, where the embryos inside the
fertilized eggs will start to develop before being laid.
Males of the genus
Tidarren amputate one of their palps before
maturation and enter adult life with one palp only. The palps are 20%
of male's body mass in this species, and detaching one of the two
improves mobility. In the Yemeni species
Tidarren argo, the remaining
palp is then torn off by the female. The separated palp remains
attached to the female's epigynum for about four hours and apparently
continues to function independently. In the meantime, the female feeds
on the palpless male. In over 60% of cases, the female of the
Australian redback spider kills and eats the male after it inserts its
second palp into the female's genital opening; in fact, the males
co-operate by trying to impale themselves on the females' fangs.
Observation shows that most male redbacks never get an opportunity to
mate, and the "lucky" ones increase the likely number of offspring by
ensuring that the females are well-fed. However, males of most
species survive a few matings, limited mainly by their short life
spans. Some even live for a while in their mates' webs.
Orange spider egg sac hanging from ceiling
Gasteracantha mammosa spiderlings next to their eggs capsule
Wolf spider carrying its young on its abdomen
Females lay up to 3,000 eggs in one or more silk egg sacs, which
maintain a fairly constant humidity level. In some species, the
females die afterwards, but females of other species protect the sacs
by attaching them to their webs, hiding them in nests, carrying them
in the chelicerae or attaching them to the spinnerets and dragging
Baby spiders pass all their larval stages inside the egg and hatch as
spiderlings, very small and sexually immature but similar in shape to
adults. Some spiders care for their young, for example a wolf spider's
brood cling to rough bristles on the mother's back, and females of
some species respond to the "begging" behaviour of their young by
giving them their prey, provided it is no longer struggling, or even
Like other arthropods, spiders have to molt to grow as their cuticle
("skin") cannot stretch. In some species males mate with newly
molted females, which are too weak to be dangerous to the males.
Most spiders live for only one to two years, although some tarantulas
can live in captivity for over 20 years.
Goliath birdeater (Theraphosa blondi), the largest spider
Spiders occur in a large range of sizes. The smallest,
Patu digua from
Colombia, are less than 0.37 mm (0.015 in) in body length.
The largest and heaviest spiders occur among tarantulas, which can
have body lengths up to 90 mm (3.5 in) and leg spans up to
250 mm (9.8 in).
Only three classes of pigment (ommochromes, bilins and guanine) have
been identified in spiders, although other pigments have been detected
but not yet characterized. Melanins, carotenoids and pterins, very
common in other animals, are apparently absent. In some species, the
exocuticle of the legs and prosoma is modified by a tanning process,
resulting in brown coloration. Bilins are found, for example, in
Micrommata virescens, resulting in its green color.
responsible for the white markings of the European garden spider
Araneus diadematus. It is in many species accumulated in specialized
cells called guanocytes. In genera such as Tetragnatha, Leucauge,
Argyrodes or Theridiosoma, guanine creates their silvery appearance.
While guanine is originally an end-product of protein metabolism, its
excretion can be blocked in spiders, leading to an increase in its
storage. Structural colors occur in some species, which are the
result of the diffraction, scattering or interference of light, for
example by modified setae or scales. The white prosoma of Argiope
results from hairs reflecting the light,
Josa both have
areas of modified cuticle that act as light reflectors.
Ecology and behavior
A jumping spider seen in Chennai.
Although spiders are generally regarded as predatory, the jumping
Bagheera kiplingi gets over 90% of its food from fairly solid
plant material produced by acacias as part of a mutually beneficial
relationship with a species of ant.
Juveniles of some spiders in the families Anyphaenidae, Corinnidae,
Salticidae feed on plant nectar.
Laboratory studies show that they do so deliberately and over extended
periods, and periodically clean themselves while feeding. These
spiders also prefer sugar solutions to plain water, which indicates
that they are seeking nutrients. Since many spiders are nocturnal, the
extent of nectar consumption by spiders may have been underestimated.
Nectar contains amino acids, lipids, vitamins and minerals in addition
to sugars, and studies have shown that other spider species live
longer when nectar is available. Feeding on nectar avoids the risks of
struggles with prey, and the costs of producing venom and digestive
Various species are known to feed on dead arthropods (scavenging), web
silk, and their own shed exoskeletons.
Pollen caught in webs may also
be eaten, and studies have shown that young spiders have a better
chance of survival if they have the opportunity to eat pollen. In
captivity, several spider species are also known to feed on bananas,
marmalade, milk, egg yolk and sausages.
Methods of capturing prey
Phonognatha graeffei or leaf-curling spider's web serves both as a
trap and as a way of making its home in a leaf.
The best-known method of prey capture is by means of sticky webs.
Varying placement of webs allows different species of spider to trap
different insects in the same area, for example flat horizontal webs
trap insects that fly up from vegetation underneath while flat
vertical webs trap insects in horizontal flight. Web-building spiders
have poor vision, but are extremely sensitive to vibrations.
Females of the water spider
Argyroneta aquatica build underwater
"diving bell" webs that they fill with air and use for digesting prey,
molting, mating and raising offspring. They live almost entirely
within the bells, darting out to catch prey animals that touch the
bell or the threads that anchor it. A few spiders use the surfaces
of lakes and ponds as "webs", detecting trapped insects by the
vibrations that these cause while struggling.
Net-casting spiders weave only small webs, but then manipulate them to
trap prey. Those of the genus
Hyptiotes and the family
Theridiosomatidae stretch their webs and then release them when prey
strike them, but do not actively move their webs. Those of the family
Deinopidae weave even smaller webs, hold them outstretched between
their first two pairs of legs, and lunge and push the webs as much as
twice their own body length to trap prey, and this move may increase
the webs' area by a factor of up to ten. Experiments have shown that
Deinopis spinosus has two different techniques for trapping prey:
backwards strikes to catch flying insects, whose vibrations it
detects; and forward strikes to catch ground-walking prey that it
sees. These two techniques have also been observed in other deinopids.
Walking insects form most of the prey of most deinopids, but one
Deinopis subrufa appears to live mainly on tipulid flies
that they catch with the backwards strike.
Mature female bolas spiders of the genus Mastophora build "webs" that
consist of only a single "trapeze line", which they patrol. They also
construct a bolas made of a single thread, tipped with a large ball of
very wet sticky silk. They emit chemicals that resemble the pheromones
of moths, and then swing the bolas at the moths. Although they miss on
about 50% of strikes, they catch about the same weight of insects per
night as web-weaving spiders of similar size. The spiders eat the
bolas if they have not made a kill in about 30 minutes, rest for a
while, and then make new bolas. Juveniles and adult males are
much smaller and do not make bolas. Instead they release different
pheromones that attract moth flies, and catch them with their front
pairs of legs.
A trapdoor spider in the genus Cyclocosmia, an ambush predator
The primitive Liphistiidae, the "trapdoor spiders" of the family
Ctenizidae and many tarantulas are ambush predators that lurk in
burrows, often closed by trapdoors and often surrounded by networks of
silk threads that alert these spiders to the presence of prey.
Other ambush predators do without such aids, including many crab
spiders, and a few species that prey on bees, which see
ultraviolet, can adjust their ultraviolet reflectance to match the
flowers in which they are lurking. Wolf spiders, jumping spiders,
fishing spiders and some crab spiders capture prey by chasing it, and
rely mainly on vision to locate prey.
Portia uses both webs and cunning, versatile tactics to overcome
Some jumping spiders of the genus Portia hunt other spiders in ways
that seem intelligent, outflanking their victims or luring them
from their webs. Laboratory studies show that Portia's instinctive
tactics are only starting points for a trial-and-error approach from
which these spiders learn very quickly how to overcome new prey
species. However, they seem to be relatively slow "thinkers",
which is not surprising, as their brains are vastly smaller than those
of mammalian predators.
An ant-mimicking jumping spider
Ant-mimicking spiders face several challenges: they generally develop
slimmer abdomens and false "waists" in the cephalothorax to mimic the
three distinct regions (tagmata) of an ant's body; they wave the first
pair of legs in front of their heads to mimic antennae, which spiders
lack, and to conceal the fact that they have eight legs rather than
six; they develop large color patches round one pair of eyes to
disguise the fact that they generally have eight simple eyes, while
ants have two compound eyes; they cover their bodies with reflective
hairs to resemble the shiny bodies of ants. In some spider species,
males and females mimic different ant species, as female spiders are
usually much larger than males. Ant-mimicking spiders also modify
their behavior to resemble that of the target species of ant; for
example, many adopt a zig-zag pattern of movement, ant-mimicking
jumping spiders avoid jumping, and spiders of the genus Synemosyna
walk on the outer edges of leaves in the same way as Pseudomyrmex.
Ant-mimicry in many spiders and other arthropods may be for protection
from predators that hunt by sight, including birds, lizards and
spiders. However, several ant-mimicking spiders prey either on ants or
on the ants' "livestock", such as aphids. When at rest, the
ant-mimicking crab spider
Amyciaea does not closely resemble
Oecophylla, but while hunting it imitates the behavior of a dying ant
to attract worker ants. After a kill, some ant-mimicking spiders hold
their victims between themselves and large groups of ants to avoid
Threat display by a
Sydney funnel-web spider
Sydney funnel-web spider (Atrax robustus).
There is strong evidence that spiders' coloration is camouflage that
helps them to evade their major predators, birds and parasitic wasps,
both of which have good color vision. Many spider species are colored
so as to merge with their most common backgrounds, and some have
disruptive coloration, stripes and blotches that break up their
outlines. In a few species, such as the Hawaiian happy-face spider,
Theridion grallator, several coloration schemes are present in a ratio
that appears to remain constant, and this may make it more difficult
for predators to recognize the species. Most spiders are
insufficiently dangerous or unpleasant-tasting for warning coloration
to offer much benefit. However, a few species with powerful venoms,
large jaws or irritant hairs have patches of warning colors, and some
actively display these colors when threatened.
Many of the family Theraphosidae, which includes tarantulas and baboon
spiders, have urticating hairs on their abdomens and use their legs to
flick them at attackers. These hairs are fine setae (bristles) with
fragile bases and a row of barbs on the tip. The barbs cause intense
irritation but there is no evidence that they carry any kind of
venom. A few defend themselves against wasps by including networks
of very robust threads in their webs, giving the spider time to flee
while the wasps are struggling with the obstacles. The golden
wheeling spider, Carparachne aureoflava, of the Namibian desert
escapes parasitic wasps by flipping onto its side and cartwheeling
down sand dunes.
Main article: Social spider
A few spider species that build webs live together in large colonies
and show social behavior, although not as complex as in social
Anelosimus eximius (in the family Theridiidae) can form
colonies of up to 50,000 individuals. The genus
Anelosimus has a
strong tendency towards sociality: all known American species are
social, and species in
Madagascar are at least somewhat social.
Members of other species in the same family but several different
genera have independently developed social behavior. For example,
Theridion nigroannulatum belongs to a genus with no other
social species, T. nigroannulatum build colonies that may contain
several thousand individuals that co-operate in prey capture and share
food. Other communal spiders include several
Agelena consociata (family Agelenidae) and Mallos
gregalis (family Dictynidae). Social predatory spiders need to
defend their prey against kleptoparasites ("thieves"), and larger
colonies are more successful in this. The herbivorous spider
Bagheera kiplingi lives in small colonies which help to protect eggs
and spiderlings. Even widow spiders (genus Latrodectus), which are
notoriously cannibalistic, have formed small colonies in captivity,
sharing webs and feeding together.
The large orb web of
Araneus diadematus (European garden spider).
There is no consistent relationship between the classification of
spiders and the types of web they build: species in the same genus may
build very similar or significantly different webs. Nor is there much
correspondence between spiders' classification and the chemical
composition of their silks.
Convergent evolution in web construction,
in other words use of similar techniques by remotely related species,
is rampant. Orb web designs and the spinning behaviors that produce
them are the best understood. The basic radial-then-spiral sequence
visible in orb webs and the sense of direction required to build them
may have been inherited from the common ancestors of most spider
groups. However, the majority of spiders build non-orb webs. It
used to be thought that the sticky orb web was an evolutionary
innovation resulting in the diversification of the Orbiculariae. Now,
however, it appears that non-orb spiders are a sub-group that evolved
from orb-web spiders, and non-orb spiders have over 40% more species
and are four times as abundant as orb-web spiders. Their greater
success may be because sphecid wasps, which are often the dominant
predators of spiders, much prefer to attack spiders that have flat
Nephila clavata, a golden orb weaver
About half the potential prey that hit orb webs escape. A web has to
perform three functions: intercepting the prey (intersection),
absorbing its momentum without breaking (stopping), and trapping the
prey by entangling it or sticking to it (retention). No single design
is best for all prey. For example: wider spacing of lines will
increase the web's area and hence its ability to intercept prey, but
reduce its stopping power and retention; closer spacing, larger sticky
droplets and thicker lines would improve retention, but would make it
easier for potential prey to see and avoid the web, at least during
the day. However, there are no consistent differences between orb webs
built for use during the day and those built for use at night. In
fact, there is no simple relationship between orb web design features
and the prey they capture, as each orb-weaving species takes a wide
range of prey.
The hubs of orb webs, where the spiders lurk, are usually above the
center, as the spiders can move downwards faster than upwards. If
there is an obvious direction in which the spider can retreat to avoid
its own predators, the hub is usually offset towards that
Horizontal orb webs are fairly common, despite being less effective at
intercepting and retaining prey and more vulnerable to damage by rain
and falling debris. Various researchers have suggested that horizontal
webs offer compensating advantages, such as reduced vulnerability to
wind damage; reduced visibility to prey flying upwards, because of the
back-lighting from the sky; enabling oscillations to catch insects in
slow horizontal flight. However, there is no single explanation for
the common use of horizontal orb webs.
Spiders often attach highly visible silk bands, called decorations or
stabilimenta, to their webs. Field research suggests that webs with
more decorative bands captured more prey per hour. However, a
laboratory study showed that spiders reduce the building of these
decorations if they sense the presence of predators.
There are several unusual variants of orb web, many of them
convergently evolved, including: attachment of lines to the surface of
water, possibly to trap insects in or on the surface; webs with twigs
through their centers, possibly to hide the spiders from predators;
"ladder-like" webs that appear most effective in catching moths.
However, the significance of many variations is unclear.
Skylab 3 took two orb-web spiders into space to test their
web-spinning capabilities in zero gravity. At first, both produced
rather sloppy webs, but they adapted quickly.
Tangleweb spiders (cobweb spiders)
A funnel web.
Members of the family
Theridiidae weave irregular, tangled,
three-dimensional webs, popularly known as cobwebs. There seems to be
an evolutionary trend towards a reduction in the amount of sticky silk
used, leading to its total absence in some species. The construction
of cobwebs is less stereotyped than that of orb-webs, and may take
Other types of webs
Linyphiidae generally make horizontal but uneven sheets, with
tangles of stopping threads above. Insects that hit the stopping
threads fall onto the sheet or are shaken onto it by the spider, and
are held by sticky threads on the sheet until the spider can attack
Spider preserved in amber
Although the fossil record of spiders is considered poor, almost
1000 species have been described from fossils. Because spiders'
bodies are quite soft, the vast majority of fossil spiders have been
found preserved in amber. The oldest known amber that contains
fossil arthropods dates from 130 million years ago in the Early
Cretaceous period. In addition to preserving spiders' anatomy in very
fine detail, pieces of amber show spiders mating, killing prey,
producing silk and possibly caring for their young. In a few cases,
amber has preserved spiders' egg sacs and webs, occasionally with prey
attached; the oldest fossil web found so far is 100 million
years old. Earlier spider fossils come from a few lagerstätten,
places where conditions were exceptionally suited to preserving fairly
The oldest known exclusively terrestrial arachnid is the trigonotarbid
Palaeotarbus jerami, from about 420 million years ago in the
Silurian period, and had a triangular cephalothorax and segmented
abdomen, as well as eight legs and a pair of pedipalps. Attercopus
fimbriunguis, from 386 million years ago in the
bears the earliest known silk-producing spigots, and was therefore
hailed as a spider at the time of its discovery. However, these
spigots may have been mounted on the underside of the abdomen rather
than on spinnerets, which are modified appendages and whose mobility
is important in the building of webs. Hence
Attercopus and the similar
Permarachne may not have been true spiders, and
probably used silk for lining nests or producing egg-cases rather than
for building webs. The largest known fossil spider as of 2011 is
the araneid Nephila jurassica, from about 165 million years ago,
recorded from Daohuogo,
Inner Mongolia in China. Its body length
is almost 25 mm, (i.e., almost one inch).
Carboniferous spiders were members of the Mesothelae, a
primitive group now represented only by the Liphistiidae. The
mesothelid Paleothele montceauensis, from the Late
299 million years ago, had five spinnerets. Although the
Permian period 299 to 251 million years ago saw rapid
diversification of flying insects, there are very few fossil spiders
from this period.
The main groups of modern spiders,
Mygalomorphae and Araneomorphae,
first appear in the
Triassic well before 200 million years ago.
Triassic mygalomorphs appear to be members of the family
Hexathelidae, whose modern members include the notorious Sydney
funnel-web spider, and their spinnerets appear adapted for building
funnel-shaped webs to catch jumping insects.
Araneomorphae account for
the great majority of modern spiders, including those that weave the
familiar orb-shaped webs. The
Cretaceous periods provide
a large number of fossil spiders, including representatives of many
Xiphosura (horseshoe crabs)
Solifugae (sun spiders)
Palpigradi (microwhip scorpions)
Amblypygi (whip spiders)
Thelyphonida (whip scorpions)
Ricinulei (hooded tickspiders)
Shultz (2007)'s evolutionary family tree of arachnids – †
marks extinct groups.
It is now agreed that spiders (Araneae) are monophyletic (i.e.,
members of a group of organisms that form a clade, consisting of a
last common ancestor and all of its descendants). There has been
debate about what their closest evolutionary relatives are, and how
all of these evolved from the ancestral chelicerates, which were
marine animals. The cladogram on the right is based on J. W. Shultz'
analysis (2007). Other views include proposals that: scorpions are
more closely related to the extinct marine scorpion-like eurypterids
than to spiders; spiders and
Amblypygi are a monophyletic group. The
appearance of several multi-way branchings in the tree on the right
shows that there are still uncertainties about relationships between
the groups involved.
Arachnids lack some features of other chelicerates, including
backward-pointing mouths and gnathobases ("jaw bases") at the bases of
their legs; both of these features are part of the ancestral
arthropod feeding system. Instead, they have mouths that point
forwards and downwards, and all have some means of breathing air.
Spiders (Araneae) are distinguished from other arachnid groups by
several characteristics, including spinnerets and, in males, pedipalps
that are specially adapted for sperm transfer.
Spiders are divided into two suborders,
Mesothelae and Opisthothelae,
of which the latter contains two infraorders,
Araneomorphae. Nearly 46,000 living species of spiders (order Araneae)
have been identified and are currently grouped into about 114 families
and about 4,000 genera by arachnologists.
(numbers are approximate)
Segmented plates on top of abdomen
Ganglia in abdomen
Striking direction of fangs
Four pairs, in some species one pair fused, under middle of abdomen
Downwards and forwards
Only in some fossils
One, two or three pairs under rear of abdomen
From sides to center, like pincers
Ryuthela sasakii, a member of the Liphistiidae
Main article: Mesothelae
The only living members of the primitive
Mesothelae are the family
Liphistiidae, found only in Southeast Asia, China, and Japan. Most
Liphistiidae construct silk-lined burrows with thin trapdoors,
although some species of the genus
Liphistius build camouflaged silk
tubes with a second trapdoor as an emergency exit. Members of the
Liphistius run silk "tripwires" outwards from their tunnels to
help them detect approaching prey, while those of genus
not and instead rely on their built-in vibration sensors. Spiders
of the genus
Heptathela have no venom glands although they do have
venom gland outlets on the fang tip.
The extinct families Arthrolycosidae, found in
Permian rocks, and Arthromygalidae, so far found only in Carboniferous
rocks, have been classified as members of the Mesothelae.
A Mexican red-kneed tarantula Brachypelma smithi
Main article: Mygalomorphae
The Mygalomorphae, which first appeared in the
are generally heavily built and hairy, with large, robust chelicerae
and fangs. Well-known examples include tarantulas, ctenizid
trapdoor spiders and the Australasian funnel-web spiders. Most
spend the majority of their time in burrows, and some run silk
tripwires out from these, but a few build webs to capture prey.
However, mygalomorphs cannot produce the pirifom silk that the
Araneomorphae use as instant adhesive to glue silk to surfaces or to
other strands of silk, and this makes web construction more difficult
for mygalomorphs. Since mygalomorphs rarely "balloon" by using air
currents for transport, their populations often form clumps. In
addition to arthropods, mygalomorphs are capable of preying on frogs,
small mammals, lizards, and snails.
Leucauge venusta, an orb-web spider
Main article: Araneomorphae
In addition to accounting for over 90% of spider species, the
Araneomorphae, also known as the "true spiders", include orb-web
spiders, the cursorial wolf spiders, and jumping spiders, as well
as the only known herbivorous spider, Bagheera kiplingi. They are
distinguished by having fangs that oppose each other and cross in a
pinching action, in contrast to the Mygalomorphae, which have fangs
that are nearly parallel in alignment.
Spiders and people
All symptoms associated with toxic spider bites
Although spiders are widely feared, only a few species are dangerous
to people. Spiders will only bite humans in self-defense, and few
produce worse effects than a mosquito bite or bee-sting. Most of
those with medically serious bites, such as recluse spiders and widow
spiders, would rather flee and bite only when trapped, although this
can easily arise by accident. Funnel web spiders' defensive
tactics include fang display and their venom, although they rarely
inject much, has resulted in 13 attributed human deaths over 50
years. They have been deemed to be the world's most dangerous
spiders on clinical and venom toxicity grounds, though this claim
has also been attributed to the Brazilian wandering spider.
There were about 100 reliably reported deaths from spider bites in the
20th century, compared to about 1,500 from jellyfish stings.
Many alleged cases of spider bites may represent incorrect
diagnoses, which would make it more difficult to check the
effectiveness of treatments for genuine bites. A review published
in 2016 agreed with this conclusion, showing that 78% of 134 published
medical case studies of supposed spider bites did not meet the
necessary criteria for a spider bite to be verified. In the case of
the two genera with the highest reported number of bites, Loxosceles
and Latrodectus, spider bites were not verified in over 90% of the
reports. Even when verification had occurred, details of the treatment
and its effects were often lacking.
Benefits to humans
Cooked tarantula spiders are considered a delicacy in Cambodia.
Spider venoms may be a less polluting alternative to conventional
pesticides, as they are deadly to insects but the great majority are
harmless to vertebrates. Australian funnel web spiders are a promising
source, as most of the world's insect pests have had no opportunity to
develop any immunity to their venom, and funnel web spiders thrive in
captivity and are easy to "milk". It may be possible to target
specific pests by engineering genes for the production of spider
toxins into viruses that infect species such as cotton bollworms.
The Ch'ol Maya use a beverage created from the tarantula species
Brachypelma vagans for the treatment of a condition they term
'tarantula wind', the symptoms of which include chest pain, asthma and
Possible medical uses for spider venoms are being investigated, for
the treatment of cardiac arrhythmia, Alzheimer's disease,
strokes, and erectile dysfunction. The peptide GsMtx-4,
found in the venom of Brachypelma vagans, is being researched to
determine whether or not it could effectively be used for the
treatment of cardiac arrhythmia, muscular dystrophy or glioma.
Because spider silk is both light and very strong, attempts are being
made to produce it in goats' milk and in the leaves of plants, by
means of genetic engineering.
Spiders can also be used as food. Cooked tarantula spiders are
considered a delicacy in Cambodia, and by the
Piaroa Indians of
southern Venezuela – provided the highly irritant hairs, the
spiders' main defense system, are removed first.
Main article: Arachnophobia
Arachnophobia is a specific phobia—it is the abnormal fear of
spiders or anything reminiscent of spiders, such as webs or
spider-like shapes. It is one of the most common specific
phobias, and some statistics show that 50% of women and 10%
of men show symptoms. It may be an exaggerated form of an
instinctive response that helped early humans to survive, or a
cultural phenomenon that is most common in predominantly European
Spiders in symbolism and culture
Main article: Cultural depictions of spiders
This Moche ceramic depicts a spider, and dates from around 300 CE.
Spiders have been the focus of stories and mythologies of various
cultures for centuries. Uttu, the ancient Sumerian goddess of
weaving, was envisioned as a spider spinning her web.
According to her main myth, she resisted her father Enki's sexual
advances by ensconcing herself in her web, but let him in after
he promised her fresh produce as a marriage gift, thereby
allowing him to intoxicate her with beer and rape her. Enki's
Ninhursag heard Uttu's screams and rescued her, removing
Enki's semen from her vagina and planting it in the ground to produce
eight previously-nonexistent plants. In a story told by the Roman
Ovid in his Metamorphoses,
Arachne was a Lydian girl who
challenged the goddess
Athena to a weaving contest. Arachne
Athena destroyed her tapestry out of jealousy,
Arachne to hang herself. In an act of mercy, Athena
Arachne back to life as the first spider. Stories
about the trickster-spider
Anansi are prominent in the folk traditions
of the Asante people of Ghana.
In some cultures, spiders have symbolized patience due to their
hunting technique of setting webs and waiting for prey, as well as
mischief and malice due to their venomous bites. The Italian
tarantella is a dance to rid the young woman of the lustful effects of
a spider bite. Web-spinning also caused the association of the spider
with creation myths, as they seem to have the ability to produce their
own worlds. Dreamcatchers are depictions of spiderwebs. The Moche
people of ancient
Peru worshipped nature. They placed emphasis on
animals and often depicted spiders in their art.
Glossary of spider terms
List of endangered spiders
List of animals that produce silk
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Find more aboutSpiderat's sister projects
Definitions from Wiktionary
Media from Wikimedia Commons
News from Wikinews
Quotations from Wikiquote
Texts from Wikisource
Textbooks from Wikibooks
Learning resources from Wikiversity
Spiders at Curlie (based on DMOZ)
Picture story about the jumping spider Aelurillus v-insignitus
New Mexico State University "The Spiders of the Arid Southwest"
Online Videos of Jumping Spiders (Salticids) and other arachnids
list of field guides to spiders, from the International Field Guides
Spider hunts on YouTube
Spider World Record: https://peerj.com/articles/3972/
Liphistiidae (segmented spiders)
Actinopodidae (mouse spiders and relatives)
Antrodiaetidae (folding trapdoor spiders)
Atypidae (atypical tarantulas or purseweb spiders)
Barychelidae (brushed trapdoor spiders)
Ctenizidae (cork-lid trapdoor spiders)
Cyrtaucheniidae (wafer trapdoor spiders)
Dipluridae (funnel-web tarantulas)
Hexathelidae (funnel-webs or venomous funnel-web tarantulas)
Mecicobothriidae (dwarf tarantulas)
Migidae (tree trapdoor spiders)
Nemesiidae (funnel-web tarantulas)
Paratropididae (bald-legged spiders)
Theraphosidae (true tarantulas)
Diguetidae (coneweb spiders)
Drymusidae (false violin spiders)
Dysderidae (woodlouse hunters)
Filistatidae (crevice weaver spiders)
Gradungulidae (large-clawed spiders)
Hypochilidae (lampshade spiders)
Leptonetidae (leptonetid spiders)
Ochyroceratidae (midget ground weavers)
Oonopidae (goblin spiders)
Pholcidae (cellar spiders)
Plectreuridae (plectreurid spiders)
Scytodidae (spitting spiders)
Segestriidae (tube-dwelling spiders)
Sicariidae (violin spiders, assassin spiders)
Telemidae (long-legged cave spiders)
Tetrablemmidae (armored spiders)
Agelenidae (araneomorph funnel weavers)
Amaurobiidae (tangled nest spiders)
Ammoxenidae (termite hunters)
Amphinectidae (including Neolanidae)
Anyphaenidae (anyphaenid sac spiders)
Araneidae (orb-weaver spiders)
Archaeidae (pelican spiders)
Clubionidae (sac spiders)
Corinnidae (dark sac spiders)
Ctenidae (wandering spiders or tropical wolf spiders)
Deinopidae (net-casting spiders)
Desidae (intertidal spiders)
Dictynidae (dictynid spiders)
Eresidae (velvet spiders)
Gnaphosidae (flat-bellied ground spiders)
Hahniidae (dwarf sheet spiders)
Hersiliidae (tree trunk spiders)
Lamponidae (white-tailed spiders)
Linyphiidae (sheet weavers or money spiders)
Liocranidae (liocranid sac spiders)
Lycosidae (wolf spiders)
Malkaridae (shield spiders)
Mimetidae (pirate spiders)
Miturgidae (long-legged sac spiders)
Mysmenidae (spurred orb-weavers)
Nesticidae (cave cobweb spiders)
Nicodamidae (red and black spiders)
Oecobiidae (disc web spiders)
Oxyopidae (lynx spiders)
Palpimanidae (palp-footed spiders)
Philodromidae (running crab spiders)
Pisauridae (nursery web spiders) (including Halidae)
Prodidomidae (long-spinneret ground spiders)
Salticidae (jumping spiders)
Senoculidae (bark hunters)
Sinopimoidae (member of Linyphiidae?)
Sparassidae (huntsman spiders)
Symphytognathidae (dwarf orb-weavers)
Tetragnathidae (long jawed orb-weavers)
Theridiidae (tangle-web spiders)
Theridiosomatidae (ray spiders)
Thomisidae (crab spiders)
Uloboridae (cribellate orb weavers)
Zodariidae (ant spiders)
Zoropsidae (zoropsid spiders)
List of families of spiders
List of spider common names
Bold are families with more than 1000 species
List of families of spiders
Lists of spider species
Palpigradi (microwhip scorpions)
Solifugae (camel spiders)
Amblypygi (cave spiders)
Schizomida (shorttailed whipscorpions)
Ricinulei (hooded tickspiders)
Classification is based on Shultz (2007)
Items in green are possibly paraphyletic groups
Fauna Europaea: 10626