'Spiders' are
predatory
invertebrate animals that have two
body segments, eight legs, no chewing mouth parts and no wings. They are classified in the
order 'Araneae', one of several orders within the larger class of
arachnids, a group which also contains
scorpions,
whip scorpions,
mites,
ticks, and
opiliones (harvestmen). The study of spiders is known as
arachnology.
All spiders produce
silk, a thin, strong
protein strand extruded by the spider from
spinnerets most commonly found on the end of the abdomen. Many species use it to trap insects in
webs, although there are also many species that hunt freely. Silk can be used to aid in climbing, form smooth walls for burrows, build egg sacs, wrap prey, and temporarily hold sperm, among other applications.
All spiders except those in the families
Uloboridae and
Holarchaeidae, and in the suborder
Mesothelae (together about 350 species) can inject
venom to protect themselves or to kill and liquefy prey. Only about 200 species, however, have
bites that can pose health problems to humans.
[1] Many larger species' bites may be quite painful, but will not produce lasting health concerns.
Spiders are found all over the world, from the tropics to the Arctic, living underwater in silken domes they supply with air, and on the tops of mountains. In 1973
Skylab 3 took two spiders into
space to test their
web-spinning capability in
free-fall.
Morphology
Spider anatomy:
(1) four pairs of
legs
(2) cephalothorax
(3) opisthosoma
Spiders, unlike
insects, have only two
body segments (tagmata) instead of three: a fused
head and
thorax (called a
cephalothorax or
prosoma) and an
abdomen (called the
opisthosoma). The exception to this rule are the
assassin spiders, whose cephalothorax seems to be almost divided into two independent units. Except for a few species of very primitive spiders (family
Liphistiidae), the abdomen is not externally segmented. The abdomen and cephalothorax are connected with a thin waist called the
pedicle or the ''pregenital somite'', a trait that allows the spider to move the abdomen in all directions. This waist is actually the last segment (somite) of the cephalothorax and is lost in most other members of the Arachnida (in scorpions it is only detectable in the embryos).
Cephalothorax
All spiders have eight legs, although a few
ant-mimicking species use their front legs to imitate
antennae, which spiders lack.
Their eyes are single
lenses rather than
compound eyes, ranging from simple light/dark-receptors to eyes rivaling those of a pigeon (some jumping spiders).
They have
pedipalps (or just ''palps''), at the base of which are
coxae or
maxillae next to their mouth that aid in ingesting food; the ends of the palp are modified in adult males into elaborate and often species-specific structures used for mating. Since they don't have any antennae, they use specialised and sensitive hairs on their legs to pick up scent, sounds, vibrations and air currents.
Spiders lack the ability to chew their food. Instead, like other arachnids, they have a tiny proboscis which they use to suck up the liquid parts of their prey. However, they are able to eat their own silk.
Sense organs
Spiders usually have eight eyes in various arrangements, a fact which is used to aid in
taxonomically classifying different species. Most species of the
Haplogynae have six eyes, although some have eight (
Plectreuridae), four (eg.,
Tetrablemma) or even two (most
Caponiidae) eyes. Sometimes one pair of eyes is better developed than the rest, or even, in some cave species, there are
no eyes at all. Several families of hunting spiders, such as
jumping spiders and
wolf spiders, have fair to excellent vision. The main pair of eyes in jumping spiders even see in color.
Net-casting spiders have enormous, compound lenses that give a wide field of view and gather available light very efficiently.
However, most spiders that lurk on flowers, webs, and other fixed locations waiting for prey tend to have very poor eyesight; instead they possess an extreme sensitivity to vibrations, which aids in prey capture. Vibration sensitive spiders can sense vibrations from such various mediums as the water surface, the soil or their silk threads. Also changes in the air pressure can be detected in the search for prey.
Respiration and circulation
Rear side of a spider
Spiders have an
open circulatory system; i.e., they do not have true
blood, or
veins to convey it. Rather, their bodies are filled with
haemolymph, which is pumped through arteries by a
heart into spaces called
sinuses surrounding their internal
organs.
Spiders have developed several different respiratory anatomies, based either 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. This system has most likely evolved in small ancestors to help resist
desiccation. The trachea were originally connected to the surroundings through a pair of spiracles, but in the majority of spiders this pair of spiracles has fused into a single one in the middle, and migrated posterior close to the spinnerets.
Among smaller araneomorph spiders we can find species who have evolved also the anterior pair of book lungs into trachea, or the remaining book lungs are simply reduced or missing, and in a very few the book lungs have developed deep channels, apparently signs of evolution into tracheae. Some very small spiders in moist and sheltered habitats have no breathing organs at all, and instead breathe directly through their body surface. In the tracheal system, oxygen interchange is much more efficient, enabling
cursorial hunting (hunting involving extended pursuit) and other advanced characteristics as having a smaller heart and the ability to live in drier habitats.
Digestion
A spider in the process of wrapping a
bluebottle caught in its web
is carried out internally and externally. Spiders that do not have powerful chelicerae, secrete digestive fluids into their prey from a series of ducts perforating their chelicerae. These digestive fluids dissolve the prey's internal tissues. Then the spider feeds by sucking the partially digested fluids out. Other spiders with more powerfully built chelicerae masticate the entire body of their prey and leave behind only a relatively small residue of indigestible materials. Spiders consume only liquid foods. Many spiders will store prey temporarily. Web weaving spiders that have made a shroud of silk to quiet their envenomed prey's death struggles will generally leave them in these shrouds and then consume them at their leisure.
Spiders are capable of digesting their own silk, so some spiders may eat their used webs. When a spider drops down on a single strand of silk and then returns, it will generally rapidly consume the strand of silk on its way back up.
Spinnerets
The abdomen has no appendages except from one to four (usually three) modified pairs of movable telescoping organs called
spinnerets, which produce
silk. The suborder ''Mesothelae'' is unique in having only two types of silk glands - thought to be the ancestral condition. All other spiders have the spinnerets further towards the posterior end of the body where they form a small cluster, and the anterior central spinnerets on the tenth segment are lost or reduced (suborder Mygalomorphae), or modified into a specialised and flattened plate called the 'cribellum' (parts of suborder ''Araneomorphae''), which produces a thread made up of hundreds to thousands of very fine dry silk fibers resulting in a woolly structure that traps prey. The cribellate spiders were the first spiders to build specialized prey catching webs.
Later some groups evolved (called ecribellate) that use silk threads dotted with sticky droplets to capture prey ranging from small arthropods to sometimes even small bats and birds.
Size
Spiders occur in a large range of sizes. Charles Churchill discovered a spider to be 600 millimeters in diameter. The smallest (members of the subfamily Erigoninae) are less than 1 mm. long (i.e., less than about .05 inches) in body length. The largest and heaviest spiders occur among
tarantulas, which can have body lengths as great as 9 cm. (i.e., about 3.5 inches) and leg spans as great as 25 cm. (i.e., about 10 inches).
[2]
Coloration
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.
[Oxford, G.S. & Gillespie, R.G. (1998). Evolution and Ecology of Spider Coloration. ''Annual Review of Entomology'' 43:619-643. ]
Bilins are found for example in ''
Micrommata virescens'', resulting in its green color. Guanine is 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, ''
Lycosa'' and ''
Josa'' both have areas of modified cuticle that act as light reflectors.
[ ]
''Pisaura mirabilis'' guarding her egg sac
Spiderlings on a web
The
exuvia of a spider after moulting
Life cycle
The spider life cycle progresses through three stages: the
embryonic, the
larval, and the nympho-imaginal.
The time between when an egg is fertilized and when the spider begins to take the shape of an adult spider is referred to as the embryonic stage. As the spider enters the larval stage, it begins to look more and more like a full grown spider. It enters the larval stage as a prelarva and, through subsequent
moults, reaches its larval form, a spider-shaped animal feeding off its yolk supply. After a few more moults (also called
instars) body structures become differentiated. Soon, all organ systems are complete and the animal begins to hunt on its own; it has reached the nympho-imaginal stage.
[3]
This stage is differentiated into two sub-stages: the nymph, or juvenile stage and the imago, or adult stage. A spider does not become
sexually mature until it makes the transition from nymph to imago.
Once a spider has reached the imago stage, it will remain there until its death. After sexual maturity is reached, the general rule is that they stop moulting, but the females of some non-araneomorph species will continue to moult the rest of their lives.
Lifespan
Many spiders may only live for about a year, but a number will live two years or more, overwintering in sheltered areas. The annual influx of 'outdoor' spiders into houses in the fall is due to this search for a warm place to spend the winter. It is common for female
tarantulas to live up to twenty years.
Reproduction
Spiders reproduce by means of
eggs, which are packed into silk bundles called ''egg sacs''. Spiders often use elaborate mating rituals (especially the visually advanced jumping spiders) to allow conspecifics to identify each other and to allow the male to approach and inseminate the female without triggering a
predatory response. If the approach signals are exchanged correctly, the male spider must (in most cases) make a timely departure after mating to escape before the female's normal predatory instincts return.
Sperm transmission from male to female occurs indirectly. When a male is ready to mate, he spins a web pad upon which he discharges his seminal fluid. He then dips his pedipalps (also known as ''palpi''), the small, leg-like appendages on the front of his
cephalothorax, into the seminal fluid, picking it up by
capillary attraction. Mature male spiders have swollen bulbs on the end of their palps for this purpose, and this is a useful way to identify the sex of a spider in the field. With his palps thus charged he goes off in search of a female. Copulation occurs when the male inserts one or both palps into the female's genital opening, known as the ''
epigyne''. He transfers his seminal fluid into the female by expanding the
sinuses in his palp. Once the sperm is inside her, she stores it in a chamber and only uses it during the egg-laying process, when the eggs comes into contact with the male sperm for the first time and are fertilized; this may be why the
vivipary has never evolved in spiders.
Very unusual behaviour is seen in spiders of the
genus ''
Tidarren'': the male amputates one of his palps before maturation and enters his adult life with one palp only. The palpi constitute 20% of the body mass of males of this species, and since this weight greatly impedes its movement, by detaching one of the two he gains increased 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.
[4]
Sacrificial males
Main articles: Spider cannibalism
It is a common belief that male spiders, which usually are significantly smaller than the females, are likely to be killed after or during mating, or sometimes even before mating can occur.
Even in some species of
black widow, which are named exactly for this belief, the male may live in the female's web for some time without being harmed. However, the male of the closely related Australian
redback spider is killed ritually by the females after it inserts its second
palpus in the female genital opening; in over 60% of cases the female then eats the male.
[5] Males that 'sacrifice' themselves gain the benefit of increasing their paternity relative to males who do not get cannibalized, by feeding the egg-laying female.
In many other species, males are sometimes killed by females. In at least some of these cases it's likely that the males are simply mistaken as prey. The risk of this happening is greater if the female is hungry. To counter this, some male spiders offer a "bribe" to the female, in form of a fly or other prey, prior to the mating.
Ecology
Spiders have a great range of variation and lifestyle, although all are
predatory.
While spiders are generalist predators, in actuality their different methods of prey capture often determine the type of prey taken. Thus web-building spiders rarely capture
caterpillars, and crab spiders that ambush prey in flowers capture more
bees,
butterflies and some flies than other insects. Groups of families that tend to take certain types of prey because of their prey capture methods are often called ''
guilds''. A few spiders are more specialized in their prey capture. ''
Dysdera'' captures and eats
sowbugs,
pillbugs and
beetles, while
pirate spiders eat only other spiders.
Bolas spiders in the family Araneidae use sex
pheromone analogs to capture only the males of certain moth species. Despite their generally broad prey ranges, spiders are one of the most important links in the regulation of the populations of
insects.
Behavior
Spiders show a wide variety of behavior, from the ballet-like mating dances of certain jumping spiders to the seeming athletics of bolas spiders snatching their prey.
Most diversity comes with the mode of predation, for example whether the spider waits for it in its orb web, or hunts it down.
Predatory techniques
Main articles: Spider diversity
A spider hiding in its leaf (located at the center of its web)
Although spider predatory technique is diverse, as soon as a spider makes contact with its prey, it will usually bite it.
Spiders bite their prey, and occasionally animals that cause them pain or threaten them, for two reasons: First, they inflict mechanical damage, which, in the case of a spider that is as large as or larger than its prey, can be severe. Second, they can inject
venom via their hollow
fangs. Many genera, such as the
widow spiders, inject
neurotoxins that can spread through the prey's entire body and interfere with vital body functions. Other genera inject venom that produces
tissue damage at the bite location. In the larger victims that do not die from these attacks,
painful lesions over a wide area can remain for an extended time. The
spitting spiders have modified their poison glands to produce a mixture of venom and sticky substance that works as glue and immobilises the prey.
Although there are no
herbivore spiders, some species in the families
Anyphaenidae,
Corinnidae,
Clubionidae,
Thomisidae and
Salticidae feed on plant
nectar.
[ Jumping spiders (Araneae: Salticidae) that feed on nectar, Jackson, R.R. ''et al.'', , , J. Zool. Lond., 2001 ] Several spider species are also known to feed on
bananas,
marmalade,
milk,
egg yolk and
sausages in captivity.
Spider webs
Main articles: Spider web
Having completed its web, a spider in the forests of Malaysia awaits its prey. Appears to be some species of
Nephila.
Some spiders spin funnel-shaped webs, others make sheet webs, spiders like the black widow make tangled, maze-like, webs, and still others make the spiral "orb" webs that are most commonly associated with spiders. These webs may be made with sticky capture silk, or with "fluffy" capture silk, depending on the type of spider. Webs may be in a vertical plane (most orb webs), a horizontal plane (sheet webs), or at any angle in between. Most commonly found in the sheet-web spider families, some webs will have loose, irregular tangles of silk above them. These tangled obstacle courses serve to disorient and knock down flying insects, making them more vulnerable to being trapped on the web below. They may also help to protect the spider from aerial predators such as birds and wasps.
The spider, after spinning its web, will then wait on, or near, the web for a prey animal to become trapped. The spider can sense the impact and struggle of a prey animal by vibrations transmitted along the web lines.
Other species of spiders do not use webs for capturing prey directly, instead pouncing from concealment (e.g. trapdoor spiders) or running them down in open chase (e.g. wolf spiders). The net-casting spider balances the two methods of running and web-spinning in its feeding habits. This spider weaves a small net which it attaches to its front legs. It then lurks in wait for potential prey and, when such prey arrives, lunges forward to wrap its victim in the net, bite and paralyze it. Hence, this spider expends less energy catching prey than a primitive hunter such as the Wolf spider. It also avoids the energy cost of weaving a large orb-web. The diving bell spider does not use its web directly in prey capture, but has modified it into an underwater diving bell. Even species whose ancestors were building spiral orb webs have given rise to spiders who no longer make webs, for instance some Hawaiian spiny-legged spiders (genus ''Tetragnatha'', family Tetragnathidae) have abandoned web construction entirely.
Some spiders manage to use the 'signaling snare' technique of a web without spinning a web at all. Several types of water-dwelling spiders will rest their feet on the water's surface in much the same manner as an orb-web user. When an insect falls onto the water and is ensnared by surface tension, the spider can detect the vibrations and run out to capture the prey.
Hunting spiders
Many spiders do not build webs for catching prey. Some examples include:
★ Brazilian wandering spider
★ Brown recluse spider
★ Huntsman spiders
★ Jumping spiders
★ Lynx spiders
★ Nursery web spiders
★ Spitting spiders
★ Tarantulas
★ Wolf spiders (Lycosidae)
★ Yellow sac spider
★ Assassin spider
Ambush predators
Some actively lure prey (the Bolas spiders) and may capture them with a sticky ball of silk on a line; others (like the crab spiders, trapdoor spiders, or the six-eyed sand spider) wait in a high-traffic area and directly attack their prey from ambush.
Defense
All spiders will attempt to protect themselves by biting, especially if they are unable to flee. Some tarantulas have a second kind of defense, a patch of urticating hairs, or urticating setae, on their abdomens, which is generally absent on modern spiders and Mesothelae. These ultra-fine hairs causes irritation and sometimes even allergic reactions in the attacker. Certain other species have specialized defense tactics. For example, the golden wheeling spider (''Carparachne aureoflava'') of the desert of Namibia escapes tarantula hawks (a species of wasp that lays its eggs in a paralyzed spider so the larvae have enough food when they hatch) by flipping onto its side and cartwheeling away.
Social spiders
A few species of spiders that build webs live together in large colonies and show social behavior, albeit not as well evolved as in social insects. The most social species is probably ''Anelosimus eximius'', which can form colonies of up to fifty thousand individuals.
Web types
Tangleweb spiders
Members of this group (family Theridiidae) are characterized by irregular, messy-looking, tangled, three-dimensional (non-sticky) webs, generally low and anchored to the ground or floor and wall. They are commonly found in or near buildings; some build webs in bushes. The spider generally hangs in the center of its web, upside-down. Prey is generally ground-dwelling insects such as ants or crickets, in addition to small flying insects. These include the infamous black widows, the minute happyface spider, and thousands of other species.
Orb web spiders
Spiders in several families (eg., Araneidae, Tetragnathidae, Nephilidae) spin the familiar spiral snare that most people think of as the typical spider web. On average, an orb-weaving spider takes 30 minutes to an hour to weave a web. They range in size from quite large (6+ cm) to very small (<1 cm), but all are quite harmless to humans, beyond the shock entailed from walking into a face-height web and having a large spider dangling from your nose. Many of the daytime hunters have a 'ferocious' appearance, with spines or large 'fangs', but they are almost invariably inoffensive, preferring to drop on a dragline to the ground when disturbed, rather than bite, which can nevertheless be quite painful.
Other forms of webs
Many other groups spin webs in a variety of structural styles.
Some (the Linyphiidae) make various forms of bowl- or dome-shaped webs with or without a flat sheet or a tangled web above or below. Some make a flat platform extending from a funnel-shaped retreat, with generally a tangle of silk above the web. The common northern hemisphere 'funnel-web', 'house' or 'grass' spiders are only superficially similar to the notorious Sydney funnel-web spider, and are generally considered to be quite harmless. Some of the more primitive group Atypidae may make tubular webs up the base of trees, from inside which they bite insects that land on the webbing. These spiders look quite ferocious, but are not generally considered to be particularly dangerous to humans.
Evolution
Main articles: Spider evolution
Trigonotarbids, spider-like arachnids, were among the oldest known land arthropods. Like spiders, they were terrestrial, respired through book lungs, and walked on eight legs with two additional legs adapted to use around their mouth. However, they were not true spiders, not even ancestral to them, but represented independent offshoots of the Arachnida.
True spiders (thin-waisted arachnids) evolved about 400 million years ago, and were among the first species to live on land. They are distinguished by abdominal segmentation and silk producing spinnerets. The Pedipalpi (including whip scorpions) are believed to constitute the sister group to the Araneae.[ Systematics and Evolution of Spiders (Araneae), Coddington, J.A. & Levi, H.W., , , Annu. Rev. Ecol. Syst., 1991 ]
Most of the early segmented fossil spiders belonged to the Mesothelae, a group of primitive spiders with the spinnerets placed underneath the middle of the abdomen, rather than at the end as in modern spiders (Opisthothelae). They were probably ground dwelling predators of other primitive arthropods. Silk may have been used simply as a protective covering for the eggs, a lining for a retreat hole, and later perhaps for simple ground sheet web and trapdoor construction.
As plant and insect life diversified so also did the spider's use of silk. Spiders with spinnerets at the end of the abdomen (Mygalomorphae and Araneomorphae) appeared more than 250 million years ago, presumably promoting the development of more elaborate sheet and maze webs for prey capture both on ground and foliage, as well as the development of the safety dragline.
By the Jurassic, the sophisticated aerial webs of the orb weaving spiders had already developed to take advantage of the rapidly diversifying groups of insects. A spider web preserved in amber, thought to be 110 million years old, shows evidence of a perfect orb web. It is believed that adhesive capture threads, as opposed to cribellate threads, evolved about 135 million years ago.[Opell, B. D. (1997). The material cost and stickiness of capture threads and the evolution of orb-weaving spiders. ''Biological Journal of the Linnean Society'' 62:443-458. ]
The ability to weave orb webs is thought to have been "lost", and sometimes even re-evolved or evolved separately, in different breeds of spiders since its first appearance.
Taxonomy
Main articles: Spider taxonomy
Almost 40,000 species of spiders (order ''Araneae'') have been identified and are currently grouped into 111 families by arachnologists, but because of difficulties in collecting these often very minute and evasive animals, and because of many specimens stored in collections waiting to be described and classified, it is believed that up to 200,000 species may exist.
The order is composed of three suborders. In the non-venomous primitive ''Mesothelae'', body segmentation is clearly visible, demonstrating the link of spiders with their segmented arthropod ancestors.
The two other suborders, the ''Mygalomorphae'' (trapdoor spiders, funnel-web spiders, tarantulas) and the ''Araneomorphae'' ("modern" spiders), are sometimes grouped together as ''Opisthothelae''. The latter account for about 94% of all spider species.
Mesothelae
''Liphistius sp.''
Main articles: Mesothelae
The Mesothelae include the only recent family Liphistiidae. Two more families (Arthrolycosidae and Arthromygalidae) are recognized from fossil evidence only.
The Liphistiidae are burrowing spiders only found in Southeast Asia, China, and Japan with about 90 species in 5 genera. Spiders of this remnant suborder are very rare, and are among the most "primitive" types of spiders in existence.
Recent Mesothelae are characterized by the narrow sternum on the ventral side of the prosoma. Several plesiomorphic characters may be useful in recognizing these spiders: there are tergite plates on the dorsal side and the almost-median position of the spinnerets on the ventral side of the opisthosoma.
Mygalomorphae
Main articles: Mygalomorphae
The Mygalomorphae are also called the Orthognatha, referring to the orientation of the fangs which point straight down and do not cross each other (cf Araneomorphae). This suborder includes the heavy bodied, stout legged spiders popularly known as tarantulas as well as the dangerous Australasian funnel-web spiders. They have ample poison glands that lie entirely within their chelicerae. Their chelicerae and fangs are large and powerful. Occasionally members of this suborder will even kill small fish, small mammals, etc. Most members of this suborder occur in the tropics and subtropics, but their range can extend farther toward the poles, e.g. into the southern and western regions of the United States and Canada, the northern parts of Europe and south into Argentina and Chile.
Araneomorphae
Main articles: Araneomorphae
The Araneomorphae, (previously called the Labidognatha), are often known as the ''modern spiders''.
They are distinguished by having chelicerae that point diagonally forward and cross in a pinching action, in contrast to the Mygalomorphae (tarantulas and their close kin), where they point straight down. Most of the spiders that people encounter in daily life belong to this suborder, which makes up 94% of all spider species.
There are approximately 95 families in this suborder, ranging from the minute ''Patu digua'' (0.37 mm) to the big and flashy ''Argiope'', from the common orb-weaver spiders to the abstruse assassin spiders, from the reclusive tree trapdoor spiders to the inquisitive jumping spiders.
Creatures often mistaken for spiders
In addition to the true spiders, there are several arachnids commonly mistaken for spiders, but which are not true spiders.
★ Camel spider, a species of solifugid (also commonly called sun-spiders or wind-scorpions), are the source of many urban legends. Although they have no venom the camel spider has been known to attack humans, focusing on exposed skin, and with fangs capable of tearing human flesh.
★ The 'daddy long-legs' or 'harvestman' is a member of the order Opiliones. These round-bodied arachnids have only two eyes and their heads are fused to their bodies. However, the name "daddy long-legs" is sometimes used to refer to cellar spiders, which have a similar leg shape; these are true spiders. Both are also often said to produce a deadly venom. While the harvestmen do not produce venom at all, the cellar spider's venom is completely harmless to humans.
Spiders and people
Spider bites
Main articles: Spider bite
Most spiders are unlikely to bite humans because they do not identify humans as prey. Spiders, even small ones, may however bite humans when pinched. For instance, a common jumping spider (Family: Salticidae), around ⅜ inch (1 cm) long, when pinched between the folds of a human's palm may inflict a bite that is about as painful as a bee sting.
Spiders in the world which have been linked to fatalities in humans, or have been shown to have potentially fatal bites by toxicology studies of their venom, include:
★ The Brazilian wandering spider
★ The Australasian funnel-web spider
★ The widow spiders, including the Australian redback spider
★ The six-eyed sand spider, and possibly other spiders of genus ''Sicarius''
★ The recluse spiders
Spiders which likely are not deadly to humans, but which are nonetheless medically significant include:
★ The hobo spider (this is doubtful, however)
★ The yellow sac spider
★ Certain species of tarantulas
★ The false black widows
Spiders which can inflict painful bites (often similar to a bee sting), but whose bites generally do not cause any systemic or long-lasting effects, include:
★ The huntsman spider
★ The redback jumping spider (not to be confused with the very dangerous redback spider, the latter being one of the widow spiders).
None of these spiders will intentionally "come after you," but they should be removed from one's house to avoid accidental injury. Many authorities warn against spraying poisons indiscriminately to kill all spiders, because doing so may actually remove one of the biological controls against incursions of the more dangerous species by ridding them of their competition.
If dangerous spiders are present in your area, be mindful when moving cardboard boxes and other such objects that may have become the shelter of a venomous spider. There is no need to be fearful; just do not grab a spider.
Spiders as food
Spiders, especially larger sorts, are eaten routinely or as a delicacy in various parts of the world, including Cambodia, Thailand, the Solomon Islands, and parts of South America.
Arachnophobia
Moche Ceramic Depicting Spider. 300 A.D.
Main articles: Arachnophobia
'Arachnophobia' is a specific phobia, an abnormal fear of spiders. It is among the most common of phobias. The reactions of arachnophobics often seem irrational to others (and sometimes to the sufferers themselves). People with arachnophobia tend to feel uneasy in any area they believe could harbor spiders or that has visible signs of their presence, such as webs. If they see a spider they may not enter the general vicinity until they overcome the panic attack that is often associated with their phobia. They may feel humiliated if such episodes happen in the presence of peers or family members. The fear of spiders can be treated by any of general techniques suggested for specific phobias.
''Arachnophobia'' is also the title of a 1990 film, as well as a spin-off video game, in which (fictitious) deadly spiders overrun a small California town.
Spiders in symbolism and culture
Main articles: Cultural depictions of spiders
There are many references to the spider in popular culture, folklore and symbolism. The spider symbolizes patience for its hunting with web traps, and mischief and malice for its poison and the slow death this causes. It symbolizes possessiveness and storage for its spinning of its prey into a ball and taking it to its burrow (for burrowing species).
Though all spiders do not spin gossamer webs, spiders have been attributed by numerous cultures with the origination of basket-weaving, knotwork, weaving, spinning and net making. Spiders are pervasive throughout folklore and mythology. Spinning and binding is evident in the etymologies of the terms religion, yoga, tantra and wyrd.
The Moche people of ancient Peru worshipped nature.[6] They placed emphasis on animals and often depicted spiders in their art. [7]
See also
★ Spider diversity
★ Identifying spiders
★ Spider webs in space
★ Endangered spiders
Footnotes
1. The global epidemiology, syndromic classification, management, and prevention of spider bites, Diaz, James H., , , American Journal of Tropical Medicine and Hygiene, 2004
2. ''Spiders and their Kin'', Herbert W. Levi and Lorna R. Levi, Golden Press, p. 20 and p. 44
3. Biology of Spiders, Foelix, Rainer F, , , , 1996,
4. {{cite journal |quotes=no |author=Knoflach, B. & van Harten, A. |year=2001 |title=''Tidarren argo'' sp. nov. (Araneae: Theridiidae) and its exceptional copulatory behaviour: emasculation, male palpal organ as a mating plug and sexual cannibalism |journal=Journal of Zoology |volume=254 |pages=449–459 |id=
5. Risky mate search and male self-sacrifice in redback spiders, Andrade, Maydianne C.B., , , Behavioral Ecology, 2003
6. Benson, Elizabeth, The Mochica: A Culture of Peru. New York, NY: Praeger Press. 1972
7. Berrin, Katherine & Larco Museum. ''The Spirit of Ancient Peru:Treasures from the Museo Arqueológico Rafael Larco Herrera.'' New York: Thames and Hudson, 1997.
References
★ Bilger, Burkhard. "Spider Woman". ''The New Yorker'', 5 March 2007, pp. 66-73.
★ The World of Spiders, W. S. Bristowe, , , Taplinger Pub Co, 1976, ISBN 0-8008-8598-8
★ Crompton, John. ''The Life of the Spider'', Mentor, 1950.
★ Hillyard, Paul. ''The Book of the Spider'', Random House, New York, 1994.
★ Kaston, B. J. ''How to Know the Spiders'', Dubuque, 1953.
★ Main, Barbara York. ''Spiders'', Collins (The Australian Naturalist Library), Sydney, 1976.
★ Ubick, Darrell; Pierre Paquin, Paula E. Cushing, and Vincent Roth. ''Spiders of North America: an Identification Manual'', American Arachnological Society, 2005.
★ Wise, David H. "Spiders in Ecological Webs." Cambridge University Press. Great Britain: 1993.
External links
General
★ The Arachnology Home Page: Araneae - Spiders
★ Spider info by Ed Nieuwenhuys
★ Deutsche Arachnologische Gesellschaft e. V. - German Arachnologic Society (EN/DE)
★
★ Spider webs in space
★ Indoor Spiders of New England Harvard University
Regional
★ Australian spiders
★ List of spiders found in Great Britain
★ University of Southern Queensland's Find-a-spider guide
★ Watson, L., and Dallwitz, M.J. 2004 onwards. The families of spiders represented in the British Isles.
★ Czech spiders with photos
★ Spiders of the Caucasus (caucasus-spiders.info)
★ Spiders of Wisconsin
Morphology
★ Histology of Salticid Spiders
Taxonomy
★ Platnick, N.I. 2005. World Spider Catalog
★ Canadian Arachnologist & Nearctic Spider Database
★ Total number of described spider genera and species
Pictures
★ Tarantulas.us - Gallery - The largest photo gallery of all tarantula's species.
★ Spiders of North America Library of reference quality large format photographs with taxonomy and descriptions.
★ Free Nature Photos, spiders
★ Macro Photography - Pictures of spiders, image gallery (commercial, but very good pictures)
Other
★ Webs made by spiders fed on drug-dosed flies
★ Spiders Research on Spiders from Science Daily.
★ University of California evaluations of spider bite severity
★ http://www.tarantulatour.com
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