Spider and Clydach, Monmouthshire: Difference between pages

Revision as of 15:18, 2 August 2006

Revision as of 13:54, 7 April 2007

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{{infobox UK place|

{{alternateuses}}

|latitude= 51.8086

{{Taxobox

|longitude= -3.1255

| color = pink

|country= Wales

| name = Spider

|official_name= Clydach

| image = Orb weaver spider day web02.jpg

|unitary_wales= [[Monmouthshire]]

| image_width = 250px

|lieutenancy_wales= [[Gwent]]

| image_caption = Orb Weaver Spider at dawn in its web

|constituency_westminster= [[Monmouth (UK Parliament constituency)|Monmouth]]

| regnum = [[Animal]]ia

|postcode_area= NP

| phylum = [[Arthropod]]a

|postcode_district= NP7

| classis = [[Arachnida]]

|dial_code= 01873

| ordo = '''Araneae'''

|os_grid_reference= SO225128

| ordo_authority = [[Carl Alexander Clerck|Clerck]], [[1757]]

|population= <2000

| diversity_link = Araneae families

}}

| diversity = <small>111 families, 40,000 species</small>

| subdivision_ranks = Suborders

| subdivision =

[[Mesothelae]]<br />

[[Mygalomorphae]]<br />

[[Araneomorphae]]<br />

''See [[Araneae families|Table of Families]]''

}}

'''Clydach''' is a village in the [[Historic counties of Wales|Welsh county]] of [[Monmouthshire]], its nearest neighbours being the towns of [[Gilwern]] and [[Abergavenny]].

'''Spiders''' are [[predator]]y [[invertebrate]] [[animal]]s that produce [[spider silk|silk]], and have two [[Tagma (biology)|tagmata]], eight legs, no chewing mouth parts and no wings. Spiders are classified in the [[order (biology)|order]] '''Araneae''', one of several orders within the larger class of [[arachnida|arachnids]], a group which also contains [[scorpion]]s, [[whip scorpion]]s, [[mite]]s, [[tick]]s, and [[Opiliones]] (harvestmen). The study of spiders is known as [[arachnology]].

It is split by the road (the 'Heads of the Valley') into North Clydach and South Clydach.

Many spiders hunt by building [[spider web|webs]] to trap [[insect]]s. These webs are made of [[spider silk]], a thin, strong [[protein]] strand extruded by the spider from [[spinneret]]s most commonly found on the end of the abdomen. For its weight, spider silk is five times stronger than steel. All spiders produce silk, although not all use it to spin elaborate traps. Silk can be used to aid in climbing, form smooth walls for burrows, build egg sacs, wrap prey, temporarily hold sperm, among many other applications.

Historically its main industry was based around the iron-works on the south side of the valley which have long since closed.

All but about 150 species of spiders (the families [[Uloboridae]] and [[Holarchaeidae]], and the [[Mesothelae]]) have the ability to inject [[venom]] to kill and liquefy prey and to protect themselves, but only up to 200 species are suspected to produce [[spider bite]]s by biting humans.<ref name="global">http://www.ajtmh.org/cgi/content/full/71/2/239 Diaz, James H. "The global epidemiology, syndromic classification, management, and prevention of spider bites", ''American Journal of Tropical Medicine and Hygiene'' 71(2), 2004, pp. 239-250</ref> Many other of the larger kinds of spiders can give bites that cause discomfort that may continue for some time but will not produce lasting effects.

The community's only school (Clydach Country Primary School) closed its gates for the final time in July 2006 after a contraversial decision by [[Monmouthshire County Council]] to shut it down, despite the protests of local residents. The reasons for the school's closure appear to have been primarily financial with the Council seeing the school as having too few pupils to justify funding. Local residents claimed however that the closure would force the children affected to travel significant distances in order to attend new schools in the area.

==Morphology==

[[Image:Archindae characters.jpg|thumb|right|180px|Spider anatomy:<br />

(1) four pairs of [[arthropod leg|legs]]<br />

(2) cephalothorax<br />

(3) opisthosoma]]

Spiders, unlike [[insect]]s, have only two [[Tagma (biology)|tagmata]] instead of three: a fused [[head (anatomy)|head]] and [[thorax]] (called a [[cephalothorax]] or [[prosoma]]) and an [[abdomen]] (called the [[:wiktionary:opisthosoma|opisthosoma]]). The exception to this rule are the [[assassin spider]]s, 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).

The area around the village is a haven for walkers and hikers with many routes tracing the beauty of the nearby Clydach Gorge.

===Spinnerets===

The abdomen has no appendages except from one to four (usually three) modified pairs of movable telescoping organs called [[spinneret]]s, which produce [[spider silk|silk]]. Originally, the common ancestor of spiders had four pairs of spinnerets, with two pairs on the tenth body segment and two pairs on the eleventh body segment, located in the middle on the ventral side of the abdomen. 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''' (suborder ''Araneomorphae''). The cribellum (usually separated into a left and a right half) produces a thread which is made up of hundreds to thousands of very fine dry silk fibers (about 0.00001 mm thick) around a few thicker core fibers, which then are<!--guessing plural here, section needs to be revised to make shorter, more intelligible sentences--> combed into a woolly structure by using a group of specialized hairs (setae) on their fourth pair of legs. It is suspected their woolly silk is charged with static electricity, causing its fine fibres to attach to trapped prey. Once all araneomorph (modern) spiders had a cribellum, but today it only remains in the cribellate spiders (although it is sometimes missing even here), which are widespread around the world. Often, this plate lacks the ability to produce silk, and is then called the '''colulus'''; an organ which zoologists have not identified a function for. The colulus is reduced or absent in most species. The cribellate spiders were the first spiders to build specialised prey catching webs, later evolving into groups which used the spinnerets solely to make webs, instead using silk threads dotted with droplets of a sticky liquid (like pearls on a necklace) to capture small arthropods, and a few large species even small bats and birds. Other spiders don't build webs at all, but have become active hunters, like the highly successful jumping spiders.

== External Links ==

===Cephalothorax===

Spiders also have eight legs (insects have six), no [[antenna (biology)|antennae]], and their eyes are single [[lens (optics)|lenses]] rather than [[compound eye]]s. They have [[pedipalp]]s (or just ''palps''), at the base of which are [[coxa]]e 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 are using specialised and sensitive hairs on their legs to pick up scent, sounds, vibrations and air currents.

[http://www.btinternet.com/~brynmawrcavingclub/caves.html Caves in the Clydach Gorge area]

Because they can't chew their food, they have, like other Arachnids, a tiny mouth they use as a short drinking straw to suck up the liquid parts of their prey. But they are able to eat their own silk (and some [[mites]] are able to eat solid particles such as spores).

[http://freespace.virgin.net/paul.benham/aber/clydach.htm Walks in the Clydach Gorge area]

== Images ==

===Respiration and circulation===

Spiders have an [[open circulatory system]]; i.e., they do not have true [[blood]], or [[vein]]s to convey it. Rather, their bodies are filled with [[haemolymph]], which is pumped through arteries by a [[heart]] into spaces called [[sinus]]es surrounding their internal [[organ (anatomy)|organs]].

((Left justified[[Image:Cldach_gorge.jpg|thumb|400px|Clydach Gorge]]))

Spiders have developed several different respiratory anatomies, based either on [[book lungs]], a [[trachea]]l 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 was 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 don't have any breathing organs at all, as they are breathing 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 dryer habitats.

===Vision===

[[Image:Jumping-spider-WA-eyes.jpg|250px|thumb|right|Multiple eyes of the jumping spider ''[[Platycryptus undatus]]''.]]

Spiders usually have eight eyes in various arrangements, a fact which is used to aid in [[taxonomic]]ally 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 [[blind spiders|no eyes]] at all. Several families of hunting spiders, such as [[jumping spider]]s and [[wolf spider]]s, have fair to excellent vision. The main pair of eyes in jumping spiders even sees in colors.

[[Category:Towns in Monmouthshire]]

[[Net-casting spider]]s have enormous, compound lenses that give a wide field of view and gather available light very efficiently. The lenses have an F number of 0.58 which means they can concentrate available light more efficiently than a cat (F 0.9) or an owl (F 1.1). Each night a large area of light sensitive membrane is manufactured within these eyes (and rapidly destroyed again at dawn). <ref>[http://www.amonline.net.au/spiders/toolkit/hairy/see.htm Australian Museum: How spiders see the world]</ref>

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.

==Life cycle==

[[Image:Spiderlings.jpg|thumb|right|250px|Spiderlings on a web]]

The spider life cycle progresses through three stages: the embryonic, the [[larva]]l, and the nympho-imaginal.<ref name="Foelix1996">Foelix, Rainer F. ''Biology of Spiders'', 2nd edition, [[1996]].</ref>

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.<ref name="Foelix1996"/> As the spider enters the larval stage, it begins to look more and more like an adult spider.<ref name="Foelix1996"/> It enters the larval stage as a prelarva and, through subsequent [[ecdysis|moults]], reaches its larval form, a spider-shaped animal feeding off its yolk supply.<ref name="Foelix1996"/> 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.<ref name="Foelix1996"/>

[[Image:Spider-skin.jpg|thumb|right|250px|The exoskeleton of a spider after moulting]]

This stage is differentiated into two sub-stages: the nymph, or juvenile stage and the imago, or adult stage.<ref name="Foelix1996"/> A spider does not become [[sexual maturity|sexually mature]] until it makes the transition from nymph to imago.<ref name="Foelix1996"/> 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-araneomorphae species will continue to moult the rest of their lives.

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 [[tarantula]]s to live around twenty years.

===Reproduction===

[[Image:Bird dropping spider03.jpg|250px|thumb|right|[[Bird Dropping Spider]] with its unusual eggs]]

[[Image:spider_egg_sac.jpg|thumb|250px|right|''Pisaura mirabilis'' guarding her egg sac, Jerusalem, Israel]]

Spiders reproduce by means of [[egg (biology)|eggs]], which are packed into silk bundles called egg sacs. Spiders often use elaborate mating rituals (especially in 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 [[predator]]y 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 [[Yemen]]i 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. <ref name="JoZo254">''Journal of Zoology'' (2001), 254:449–459 [[Cambridge University Press]] {{DOI|10.1017/S0952836901000954}}</ref>

<br clear=all />

===Sacrificial males===

It is often said that the male (usually significantly smaller than the female, down to 1% of her size as seen in ''[[Tidarren sisyphoides]]'') is likely to be killed by the female after the coupling, or sometimes even before intercourse has been initiated. This supposed propensity is what gave the [[black widow spider]], ''Latrodectus mactans'', its name. However, the three species of [[North America]]n black widows do not seem to usually kill the male (although they have been known to). Males can sometimes even live in the web of a female for a while without being harmed in any way. The male Australian [[red-back spider|redback spider]] ''Latrodectus hasselti'' 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.

Although the male ''Latrodectus hasselti'' may sometimes die during mating without the female actually consuming it, this species represents a possible strategy of "male sacrifice". The male redback, while copulating, 'somersaults' and twists its abdomen directly onto the fangs of its mate. Most males get consumed at this stage (Maydianne CB Andrade reports 65%).<ref name="Andrade2003">Andrade, Maydianne C.B. ''Behavioral Ecology'' (2003), 14:531–538</ref> Males that 'sacrifice' themselves gain the benefit of increasing their paternity relative to males who do not get cannibalized.<ref name="Andrade2003"/>

[[Image:Spider.jpg|thumb|250px|left|''Miturga species'' in web under rock]]

However, despite these examples and many other similar reports, the theory of the 'sacrificial male' has become greater than the truth. Mating of spiders is not always followed by cannibalism. Foelix writes, "The supposed aggressiveness of the female spider towards the male is largely a myth... only in some exceptional cases does the male fall victim to the female." <ref name="Foelix-1982">Foelix, Rainer F. ''Biology of Spiders'', [[1982]].</ref> Michael Roberts says, "It is rare for a fit male to be eaten by the female."<ref name="Roberts">Roberts, Michael J. ''Spiders of Britain and Northern Europe'', Collins, London, [[1995]].</ref> And yet, spider cannibalism has been proved to occur in some species more than in others, mainly species belonging to ''Latrodectus''.

<!--THIS IS REPEATING INFORMATION ALREADY GIVEN ABOVE-->There has always been speculation on why this sacrifice of male mates might occur despite the fact that there is an obvious disadvantage to the sacrificial males. One theory is that once the male has mated, he is unlikely to mate again and so any further extension of his life is of lesser [[evolution]]ary benefit than his indirectly contributing [[nutrition]] to the eggs. Having more offspring would give the male the advantage of having his genes passed on over other males that might avoid being eaten. This scenario would be consistent with the hypothesis of Roberts that old or unfit males get eaten, whilst younger and fitter ones may survive to mate again.<ref name="Roberts"/>

==Ecology==

Spiders have a great range of variation and lifestyle, although all are [[predator]]y.

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 [[caterpillar]]s, and crab spiders that ambush prey in flowers capture more [[bee]]s, [[butterfly|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 [[insect]]s. Every day on a meadow they devour over 10 g/m² of insects and other arthropods. {{citation needed}} <br>

===Predatory techniques===

[[Image:Spider house leaf.jpg|thumb|right|250px|A spider hiding in its leaf (located at the centre of its web)]]

There are many families of spiders, and the ways that they catch [[prey]] are diverse. But whether they catch [[insect]]s, [[fish]], small [[mammal]]s, small [[bird]]s, or some other small form of life, as soon as a spider makes contact with its prey it will generally attempt to bite it.

Spiders bite their prey, and occasionally animals that cause them pain or threaten them, to do two things. 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 choose to inject [[Venom (poison)|venom]] through their hollow [[fang]]s. Many genera, such as the [[widow spider]]s, inject [[neurotoxin]]s that can spread through the prey's entire body and interfere with vital body functions. Other genera inject venom that operates to produce [[biological tissue|tissue]] damage at the site of the bite. Genera such as that of the [[brown recluse spider]] produce a necrotoxin. The necrotoxin is injected into prey where it causes the degradation of cell membranes. In the larger victims that do not die from these attacks, [[pain]]ful lesions over a fairly wide area of the body can remain active for fairly long periods of time. The spitting spiders have modified their poison glands to produce a mixture of venom and sticky substance that works as glue and immobilise the prey.

[[Digestion]] 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 glob 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.

Although there are no [[vegetarian]] spiders, some species in the families [[Anyphaenidae]], [[Corinnidae]], [[Clubionidae]], [[Thomisidae]] and [[Salticidae]] have been observed feeding on plant [[nectar]]<ref name=Jackson2001>Jackson, R.R. et. al. (2001). Jumping spiders (Araneae: Salticidae) that feed on nectar. ''J. Zool. Lond. 255:25-29 [http://xnelson.googlepages.com/Jacksonetal2001.pdf PDF]</ref>.

Several spider species are also known to feed on bananas, marmalade, milk, egg yolk and sausages in captivity.<ref name=Jackson2001/>

===Spider webs and prey capture===

{{main|Spider web}}

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.

[[Image:Spider01250.jpg|thumb|right|250px|Having completed its web, a spider in the forests of Malaysia awaits its prey. Appears to be some species of Nephila.]]

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 spider]]s) or running them down in open chase (e.g. [[wolf spider]]s). 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]]) which have abandoned web construction entirely.

Some spiders manage to use the 'signalling 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.

[[Image:Spider Chiapas Mexico.jpg|thumb|right|250px|A [[golden silk orb-weaver]] (''Nephila clavipes''?), member of the family [[Tetragnathidae]]]]

===Defense===

All spiders will attempt to protect themselves by biting, especially if they are unable to flee. Some [[tarantula]]s have a second kind of defense, a patch of [[urticating hair]]s, or urticating setae, on their abdomens, which is generally absent on [[Araneomorphae|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 hawk]]s (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 are living together in large colonies and are showing social behavior, even if it is not as well evolved as in [[Eusociality|social insects]]. The most social species are probably ''[[Anelosimus eximius]]'', which can form colonies that counts up to fifty thousand individuals.

==Evolution==

{{main|Spider evolution}}

[[Trigonotarbid]]s, 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 [[spinneret]]s.

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 [[Spider web|orb web]].

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|Spider taxonomy}}

Almost 40,000 [[species (biology)|species]] of spiders (order ''Araneae'') have been identified and are currently grouped into 111 [[family (biology)|families]] by [[arachnology|arachnologists]], but because of difficulties in collecting these often very minute and evasive animals, and because of many [[specimen (biology)|specimens]] stored in [[collection (museum)|collection]]s 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, [[tarantula]]s) and the ''[[Araneomorphae]]'' ("modern" spiders), are sometimes grouped together as ''Opisthothelae''. The latter account for about 94% of all spider species.

=== Mesothelae ===

{{main|Mesothelae}}

[[Image:Liphistius.sp.small.jpg|thumb|right|250px|''Liphistius sp.'']]

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 (biology)|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|Mygalomorphae}}

[[Image:Brachypelma Smithii.jpg|thumb|250px|right|The tarantula ''[[Brachypelma smithi]]'']]

The ''Mygalomorphae'' are also called the ''Orthognatha'', referring to the orientation of the [[Cheliceral fang|fang]]s which point straight down and do not cross each other (cf [[Araneomorphae]]). This suborder includes the heavy bodied, stout legged spiders popularly known as [[tarantula]]s as well as the dangerous [[Australasian funnel-web spider]]s. 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 [[mammal]]s, 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===

[[Image:Araneus diadematus (aka).jpg|thumb|right|250px|''[[Araneus diadematus]]'']]

[[Image:Gasteracantha.cancriformis.jpg|thumb|200px|left|[[Gasteracantha|Spinyback orbweaver]]]]

{{main|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 [[Spider families|95 families]] in this suborder, ranging from the minute ''[[Patu digua]]'' (0.37mm) to the big and flashy ''[[Argiope (spider)|Argiope]]'', from the common [[Orb-weaver spider]]s to the abstruse [[assassin spider]]s, from the reclusive [[Migidae|tree trapdoor spiders]] to the inquisitive [[jumping spider]]s.

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==Diversity==

{{main|Spider diversity}}

===Tangleweb spiders===

[[Image:Latrodectus mactans.jpg|thumb|150px|right|[[Latrodectus mactans|Black widow]]]]

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 [[Theridion grallator|Happyface spider]], and thousands of other species.

===Orb web spiders ===

[[Image:NephilaClavata-2005Kurihara.jpg|thumb|200px|right|A [[Nephila clavata|Golden Orb Weaver]]]]

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+&nbsp;cm) to very small (<1&nbsp;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.

[[Image:Ant_Mimic_Spider.jpg|250px|thumb|right|An [[Myrmarachne|ant-mimicking jumping spider]]]]

Many spiders do not build webs for catching prey. Some examples include:

* [[Brazilian wandering spider]]

* [[Brown recluse spider]]

* [[Huntsman spider]]s

* [[Jumping spider]]s

* [[Lynx spider]]s

* [[Nursery web spider]]s

* [[Spitting spider]]s

* [[Tarantula]]s

* [[Wolf spider]]s (Lycosidae)

* [[Yellow sac spider]]

* [[Assassin spider]]

===Ambush predators===

Some actively lure prey (the [[Bolas spider]]s) and may capture them with a sticky ball of silk on a line; others (like the [[Thomisidae|crab spiders]], [[trapdoor spider]]s, or the [[Sicarius hahnii|six-eyed sand spider]]) wait in a high-traffic area and directly attack their prey from ambush.

==Spider bites==

[[Image:Atrax robustus.jpg|thumb|240px|right|Sydney funnel-web spider]]

{{main|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 3/8&nbsp;inch (1&nbsp;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 [[Six-eyed sand spider]], and possibly other spiders of genus ''Sicarius''

* The [[widow spider]]s

* The [[recluse spider]]s

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 [[tarantula]]s

* The [[Steatoda|false black widow]]s

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 [[Phidippus johnsoni|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 poisonous spider. There is no need to be fearful; just do not grab a spider.

==Spiders in symbolism and culture==

{{main|Spiders in popular culture}}

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 symbolises possessiveness for its spinning its prey into a ball and taking it to its burrow (for burrowing species).

==Creatures often mistaken for spiders==

* [[Camel spider]], a species of [[solifugid]] (also commonly called sun-spiders or wind-scorpions), are the source of many [[urban legend]]s. In spite of their bad reputation they are actually harmless to humans, and have no venom.

* 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 [[Daddy long-legs spider|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 don't produce venom at all, the cellar spider's venom is completely harmless to humans.

==See also==

* For a guide to identifying spiders, see [[Identifying spiders|Spider finder]].

*[[Wikipedia:List of images/Nature/Animals/Spiders|The spider gallery]]

==References==

<references/>

*{{cite book|title=The World of Spiders|author=[[W. S. Bristowe]]|publisher=Taplinger Pub Co|id=ISBN 0800885988|year=1976}}

*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==

{{commons|Spider}}

===General===

*[http://www.arachnology.org/Arachnology/Pages/Araneae.html Arachnology Home Pages: Araneae]

*[http://www.xs4all.nl/~ednieuw/Spiders/InfoNed/The_spider.html Spider info by Ed Nieuwenhuys]

*[http://www.dearge.de/english.php Deutsche Arachnologische Gesellschaft e. V. - German Arachnologic Society (EN/DE)]

===Regional===

*[http://www.amonline.net.au/spiders/ Australian spiders]

*[http://www.britishspiders.org.uk/html/info.html List of spiders found in Great Britain]

*[http://delta-intkey.com/britsp Watson, L., and Dallwitz, M.J. 2004 onwards. The families of spiders represented in the British Isles.]

===Morphology===

* [http://www.users.qwest.net/~phidippus/page10.htm Histology of Salticid Spiders]

===Taxonomy===

*[http://research.amnh.org/entomology/spiders/catalog81-87/index.html Platnick, N.I. 2005. World Spider Catalog]

*[http://canadianarachnology.webhop.net Canadian Arachnologist & Nearctic Spider Database]

*[http://research.amnh.org/entomology/spiders/catalog/COUNTS.html Total number of described spider genera and species]

===Pictures===

*[http://www.tarantulas.us/gallery/ gallery.tarantulas.us] - Pictures of Tarantulas/Spiders

*[http://www.cirrusimage.com/spider.htm Spiders of North America] Library of reference quality large format photographs with taxonomy and descriptions.

*[http://www.free-nature-photos.org/en/Spiders/ Free pictures of polish spiders]

===Other===

*[http://www.cannabis.net/weblife.html Webs made by spiders fed on drug-dosed flies]

*[http://www.surviveoutdoors.com/emergency/spiderbites.asp Spider Bites] - Pictures and treatment information presented by Survive Outdoors, Inc.

*[http://spiders.ucr.edu/dermatol.html University of California evaluations of spider bite severity]

[[Category:Spiders|*]]

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