Spider taxonomy is the part of taxonomy that is concerned with the science of naming, defining and classifying all spiders , members of the Araneae order of the arthropod class Arachnida , which has more than 48,500 described species . However, there are likely many species that have escaped the human eye as well as specimens stored in collections waiting to be described and classified. It is estimated that only one-third to one half of the total number of existing species have been described.
93-429: See text . The spider genus Steatoda , in the family Theridiidae , includes about 120 recognized species , distributed around the world (including many cosmopolitan species which are found among human populations worldwide). One common name is cupboard spider , for many species build their webs in dark, sheltered, undisturbed places around the house or garden, in sheds and garages, under garden, in compost bins, and
186-530: 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 comblike 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
279-467: A mutualistic relationship with a species of ant . Juveniles of some spiders in the families Anyphaenidae , Corinnidae , Clubionidae , Thomisidae and 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,
372-406: 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
465-493: 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 . Airborne fungal spores caught on the webs of orb-weavers may be ingested along with the old web before construction of a new web. The enzyme chitinase present in their digestive fluid allows for the digestion of these spores. Spiders have been observed to consume plant material belonging to
558-412: A combination of lightness, strength and elasticity superior to 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 irrational fear of spiders
651-501: A dorsal line or triangular shapes or both. Orange to reddish-marked Steatoda paykulliana can be mistaken for the redback spider ). In common with other members of the family Theridiidae, Steatoda construct a tangled web, i.e., an irregular tangle of sticky silken fibers. These spiders have very poor eyesight and depend mostly on vibrations reaching them through their webs to orient themselves to prey or to warn them of larger animals that could injure or kill them. As of May 2024,
744-402: 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
837-467: A few to 50,000 individuals. Social behavior ranges from precarious toleration, as in the widow spiders , to cooperative 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 non-polluting pesticides . Spider silk provides
930-424: 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
1023-706: A large variety of taxa and type. Conversely, cursorial spiders comprise the vast majority (over 80%) of reported incidents of plant-eating. 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. The water spider Argyroneta aquatica build underwater "diving bell" webs that they fill with air and use for digesting prey and molting. Mating and raising
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#17327984013451116-493: 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
1209-590: A reduced number of eyes, the most common having six eyes (example, Periegops suterii ) with a pair of eyes absent on the anterior median line . Other species have four eyes and members of the Caponiidae family can have as few as two. Cave dwelling species have no eyes (such as the Kauaʻi cave wolf spider ), or possess vestigial eyes incapable of sight (such as Holothele maddeni ). As with other arthropods, spiders' cuticles would block out information about
1302-531: A separate common origin (i.e. being synapomorphies ). One phylogenetic hypothesis based on molecular data shows the Haplogynae as a paraphyletic group leading to the Austrochilidae and Entelegynae. The Entelegynae have a more complex reproductive anatomy: females have two "copulatory pores" in addition to the single genital pore of other groups of spiders; males have complex palpal bulbs, matching
1395-440: 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. 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
1488-476: 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
1581-409: 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
1674-495: A spider gets unintentionally squeezed or pinched somehow. It is possible that some bites result when a spider mistakes a finger thrust into its web for its normal prey, but ordinarily intrusion by any large creature will cause these spiders to flee. Spider See Spider taxonomy . Spiders ( order Araneae ) are air-breathing arthropods that have eight limbs, chelicerae with fangs generally able to inject venom , and spinnerets that extrude silk . They are
1767-586: A very small proportion of the total of around 49,000 known species. Mygalomorphae species comprise around 7% of the total, the remaining 93% being in the Araneomorphae. Mesothelae Mygalomorphae Austrochiloidea Entelegynae Haplogynae Hypochiloidea The Araneomorphae are divided into two main groups: the Haplogynae and the Entelegynae . The Haplogynae make up about 10% of
1860-571: Is called arachnophobia . The word spider derives from Proto-Germanic * spin-þron- , literally ' spinner ' (a reference to how spiders make their webs), from the Proto-Indo-European root * (s)pen- ' to draw, stretch, spin ' . 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
1953-530: Is correct, the earliest members of the Entelegynae made webs defined by the substrate on which they were placed (e.g. the ground) rather than suspended orb webs. True orb webs evolved once, in the ancestors of the Orbiculariae, but were then modified or lost in some descendants. An alternative hypothesis, supported by some molecular phylogenetic studies, is that the Orbiculariae are paraphyletic , with
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#17327984013452046-483: Is hardly necessary to categorize one of them as a mygalomorph. Other, smaller, members of this suborder, however, look little different from the araneomorphs. (See the picture of Sphodros rufipes below.) Many araneomorphs are immediately identifiable as such since they are found on webs designed for the capture of prey or exhibit other habitat choices that eliminate the possibility that they could be mygalomorphs. Spiders in infraorder Mygalomorphae are characterized by
2139-468: 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
2232-569: 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 bristles reflecting the light, Lycosa and Josa both have areas of modified cuticle that act as light reflectors. The peacock spiders of Australia (genus Maratus ) are notable for their bright structural colours in
2325-401: 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 upper surface. Like other arthropods, spiders are coelomates in which the coelom is reduced to small areas around the reproductive and excretory systems. Its place is largely taken by a hemocoel , a cavity that runs most of
2418-451: Is strong evidence that orb webs evolved only once, although only weak support for the monophyly of the Orbiculariae. One possible phylogeny is shown below; the type of web made is shown for each terminal node in order of the frequency of occurrence. Eresoidea, RTA clade – no web; substrate-defined web Deinopoidea – orb web Araneoidea – orb web ; aerial sheet web ; cobweb ; no web Nicodamidae – aerial sheet web If this
2511-486: Is successful, the male injects his sperm from the palpal bulbs into the female via one or two openings on the underside of her abdomen. Female spiders' reproductive tracts are arranged in one of two ways. The ancestral arrangement ("haplogyne" or "non-entelegyne") consists of a single genital opening, leading to two seminal receptacles (spermathecae) in which females store sperm. In the more advanced arrangement ("entelegyne"), there are two further openings leading directly to
2604-482: 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
2697-415: 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. Some spiders use their webs for hearing, where the giant webs function as extended and reconfigurable auditory sensors. Each of the eight legs of
2790-549: The Araneoidea are ecribellate – the adhesive properties of their webs are created by fine droplets of "glue". In spite of these differences, the webs of the two groups are similar in their overall geometry. The evolutionary history of the Entelegynae is thus intimately connected with the evolutionary history of orb webs. One hypothesis is that there is a single clade, Orbiculariae, uniting the orb web makers, in whose ancestors orb webs evolved. A review in 2014 concluded that there
2883-653: 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, more than 200 million years ago . The species Bagheera kiplingi
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2976-1024: The World Spider Catalog accepted the following extant species: Those commonly mistaken for widows include: Other notable and recognizable species in the genus include: Steatoda is known to prey on other spiders (including true black widows ), crickets, ladybugs, cockroaches , and woodlice . Some members of this genus do have bites which are reported to have generalized symptoms in humans (such as S. grossa and S. nobilis ). However total number of cases are rare with one ever in France and England each, and 5 in Ireland. A review by Isbister noted 23 over 3 years in Australia. No bites require medical treatment. However, bites by Steatoda species generally do not have any long-lasting effects. Symptoms can include moderate to severe pain increasing for
3069-629: The exocuticle of the legs and prosoma is modified by a tanning process, resulting in a brown coloration. 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
3162-499: The genus Tidarren amputate one of their palps before maturation and enter adult life with one palp only. The palps are 20% of the 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
3255-512: The jumping spiders that patrol the outside walls of buildings, and so on. They are characterized by having fangs whose tips approach each other as they bite, and (usually) having one pair of book lungs . Spiders were long classified into families that were then grouped into superfamilies, some of which were in turn placed into a number of higher taxa below the level of infraorder. When more rigorous approaches, such as cladistics , were applied to spider classification, it became clear that most of
3348-481: The thorax . Similarly, arguments can be formed against the use of the term "abdomen", as the opisthosoma of all spiders contains a heart and respiratory organs, organs atypical of an abdomen. 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
3441-415: The Entelegynae. Although some studies based on both morphology and DNA suggest that the Haplogynae form a monophyletic group (i.e. they comprise all the descendants of a common ancestor), this hypothesis has been described as "weakly supported", with most of the distinguishing features of the group being inherited from ancestors shared with other groups of spiders, rather than being clearly indicative of
3534-695: The Haplogynae. Earlier analyses regarded the Hypochiloidea as the sole representatives of a group called the Paleocribellatae, with all other araneomorphs placed in the Neocribellatae. The Haplogynae are a group of araneomorph spiders with simpler male and female reproductive anatomy than the Entelegynae. Like the mesotheles and mygalomorphs, females have only a single genital opening ( gonopore ), used both for copulation and egg-laying; males have less complex palpal bulbs than those of
3627-463: The abdomen becomes green. Environmentally induced color changes may be morphological (occurring over several days) or physiological (occurring near instantly). Morphological changes require pigment synthesis and degradation. In contrast to this, physiological changes occur by changing the position of pigment-containing cells. An example of morphological color changes is background matching. Misumena vatia for instance can change its body color to match
3720-414: The ability to use a trial-and-error approach. 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
3813-432: 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
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3906-412: The black widow, and Steatoda castanea looks more like a brown widow . The colour can range from sandy pale brown to reddish plum to satiny black. Like most spiders, its cephalothorax is smaller than its abdomen , which is somewhat egg-shaped, and can have white or beige to orange markings. Although sometimes not or partially visible, these markings usually consists of a frontal crescent, often with
3999-404: The cephalothorax acts as a pump that sends the food deeper into the digestive system. The midgut 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
4092-579: The cephalothorax. Unlike most arthropods, spiders have no extensor muscles in their limbs and instead extend them by hydraulic pressure. Their abdomens bear appendages, 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-weaver spiders . Spider-like arachnids with silk-producing spigots ( Uraraneida ) appeared in
4185-619: The cribellum. 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 species. 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 onto which they ejaculate and then transfer
4278-430: 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
4371-496: The ensuing 250 years, thousands more species have been described by researchers around the world, yet only a dozen taxonomists are responsible for more than one-third of all species described. The most prolific authors include Eugène Simon of France, Norman Platnick and Herbert Walter Levi of the United States, Embrik Strand of Norway, and Tamerlan Thorell of Sweden, each having described well over 1,000 species. At
4464-505: The evolutionary chronicle and the underlying diversity patterns that have resulted in one of the most extraordinary radiations of animals". Mesothelae resemble the Solifugae ("wind scorpions" or "sun scorpions") in having segmented plates on their abdomens that create the appearance of the segmented abdomens of these other arachnids. They are both few in number and also limited in geographical range. Suborder Opisthothelae contains
4557-566: 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 enzymes. 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
4650-505: The female genital structures ( epigynes ). The monophyly of the group is well supported in both morphological and molecular studies. The internal phylogeny of the Entelegynae has been the subject of much research. Two groups within this clade contain the only spiders that make vertical orb webs: the Deinopoidea are cribellate – the adhesive properties of their webs are created by packets of thousands of extremely fine loops of dry silk;
4743-501: The females, which are typically much larger, male spiders identify themselves as 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
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#17327984013454836-513: The first hour (without severe sweating). Some people have reported mild to moderate nausea, headache, and lethargy. The duration of all symptoms and effects can range from 1 to 60 hours. The symptoms associated with the bite of several Steatoda species have been named steatodism ; and have been described as a less-severe form of latrodectism (the symptoms associated with a widow spider bite). The redback spider antivenom has been thought to be effective at treating bites from S. grossa , after it
4929-478: 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
5022-586: The largest order of arachnids and rank seventh in total species diversity among all orders of organisms . Spiders are found worldwide on every continent except Antarctica , and have become established in nearly every land habitat . As of September 2024 , 52,309 spider species in 134 families have been recorded by taxonomists . However, there has been debate among scientists about how families should be classified, with over 20 different classifications proposed since 1900. Anatomically , spiders (as with all arachnids) differ from other arthropods in that
5115-406: 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
5208-605: The like. Signs of the cupboard spider include small white spots of spider droppings, like small splashes of paint, on the floor underneath the web. Many spiders of the genus Steatoda are often mistaken for widow spiders ( Latrodectus ), and are known as false widows . The two genera are closely related – both occurring in the same family, Theridiidae – but Steatoda are significantly less harmful to humans. Not all Steatoda species resemble black widows – they come in many different colors and sizes, mostly smaller than Latrodectus species. Steatoda paykulliana can grow larger than
5301-418: 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. 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
5394-445: The major groupings used in the 20th century were not supported. Many were based on shared characteristics inherited from the ancestors of multiple clades ( plesiomorphies ), rather than being distinct characteristics originating in the ancestors of that clade only ( apomorphies ). According to Jonathan A. Coddington in 2005, "books and overviews published prior to the last two decades have been superseded". Listings of spiders, such as
5487-433: The males. While in many spiders color is fixed throughout their lifespan, in some groups, color may be variable in response to environmental and internal conditions. Choice of prey may be able to alter the color of spiders. For example, the abdomen of Theridion grallator will become orange if the spider ingests certain species of Diptera and adult Lepidoptera , but if it consumes Homoptera or larval Lepidoptera, then
5580-859: The males. Most spiders live for only one to two years, although some tarantulas can live in captivity for over 20 years, and an Australian female trapdoor spider was documented to have lived in the wild for 43 years, dying of a parasitic wasp attack. 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,
5673-462: 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
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#17327984013455766-402: 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
5859-559: 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 regurgitate food. In one exceptional case, females of the jumping spider Toxeus magnus produce a nutritious milk-like substance for their offspring, and fed until they are sexually mature. 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
5952-698: 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
6045-414: The mouth; in addition, those of male spiders have enlarged last sections used for sperm transfer. 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
6138-541: The number of species in the families is bound to change and only reflects the present state of knowledge. Nevertheless, the species numbers given here are useful as a guideline – see the table of families at the end of the article. Spider taxonomy can be traced to the work of Swedish naturalist Carl Alexander Clerck , who in 1757 published the first binomial scientific names of some 67 spiders species in his Svenska Spindlar ("Swedish Spiders"), one year before Linnaeus named over 30 spiders in his Systema Naturae . In
6231-550: The offspring happens in the female's bell. 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. Spider taxonomy Arachnologists currently divide spiders into two suborders with about 129 families . Due to constant research, with new species being discovered every month and others being recognized as synonyms ,
6324-522: 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 1,000 such chemosensitive setae, most on
6417-442: The ovarian cavity where fertilization occurs. The only known example of direct fertilization between male and female is an Israeli spider, 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
6510-609: The phylogeny of the Entelegynae being as shown below. Araneoidea – orb web ; aerial sheet web ; cobweb ; no web Deinopoidea , Oecobiidae – orb web ; substrate-defined web RTA clade – no web; substrate-defined web On this view, orb webs evolved earlier, being present in the early members of the Entelegynae, and were then lost in more groups, making web evolution more convoluted, with different kinds of web having evolved separately more than once. Future advances in technology, including comparative genomics studies, and whole-genome sampling should lead to "a clearer image of
6603-442: 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 tracheal 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
6696-551: The propulsive force for their jumps. Most spiders that hunt actively, rather than relying on webs, have dense tufts of fine bristles 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
6789-413: 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 ,
6882-429: The roots of the chelicerae. The families 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 two sets of filters to keep solids out. They use one of two different systems of external digestion. Some pump digestive enzymes from
6975-417: 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 them along. Baby spiders pass all their larval stages inside the egg sac and emerge 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 clings to rough bristles on
7068-465: The secondary eyes are immobile. The visual acuity of some jumping spiders exceeds by a factor of ten that of dragonflies , which have by far the best vision among insects . This acuity is achieved by a telephotographic series of lenses, a four-layer retina, and the ability to swivel the 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
7161-456: The sexes apart, it is assumed the blood scent is mixed with pheromones. Spiders also have in the joints of their limbs slit sensillae that detect 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
7254-457: The sperm to special syringe -styled 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 "smell". Spiders generally use elaborate courtship rituals to prevent
7347-428: The spermathecae, creating a "flow through" system rather than a "first-in first-out" one. Eggs are as a general rule only fertilized during oviposition when the stored sperm is released from its chamber, rather than in the ovarian cavity. A few exceptions exist, such as Parasteatoda tepidariorum . In these species the female appears to be able to activate the dormant sperm before oviposition, allowing them to migrate to
7440-504: The spiders that have no plates on their abdomens. Opisthothelae is divided into two infraorders, Mygalomorphae and Araneomorphae, which can be distinguished by the orientation of their fangs. It can be somewhat difficult on casual inspection to determine whether the fang orientation would classify a spider as a mygalomorph or araneomorph. The spiders that are called " tarantulas " in English are so large and hairy that inspection of their fangs
7533-492: The substrate it lives on which makes it more difficult to be detected by prey. An example of physiological color change is observed in Cyrtophora cicatrosa , which can change its body color from white to brown near instantly. Although spiders are generally regarded as predatory, the jumping spider Bagheera kiplingi gets over 90% of its food from Beltian bodies , a solid plant material produced by acacias as part of
7626-440: The surface while walking or running. 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. Spitting spiders also produce silk in modified venom glands. Silk
7719-414: The tapeta. On the other hand, the secondary eyes of jumping spiders have no tapeta. 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,
7812-436: The tarsi of the first pair of legs. Males have more chemosensitive bristles on their pedipalps than females. They have been shown to be responsive to sex pheromones produced by females, both contact and air-borne. The jumping spider Evarcha culicivora uses the scent of blood from mammals and other vertebrates, which is obtained by capturing blood-filled mosquitoes , to attract the opposite sex. Because they are able to tell
7905-559: 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
7998-490: The total number of spider species, the Entelegynae about 83%. The phylogenetic relationships of the Haplogynae, Entelegynae and the two smaller groups Hypochiloidea and Austrochiloidea remain uncertain as of 2015 . Some analyses place both Hypochiloidea and Austrochiloidea outside Haplogynae; others place the Austrochiloidea between the Haplogynae and the Entelegynae; the Hypochiloidea have also been grouped with
8091-401: The tubules of insects and arachnids develop from completely different parts of the embryo . However, a few primitive spiders, the suborder Mesothelae and infraorder Mygalomorphae , retain the ancestral arthropod nephridia ("little kidneys "), which use large amounts of water to excrete nitrogenous waste products as ammonia . The basic arthropod central nervous system consists of
8184-418: The usual body segments are fused into two tagmata , the cephalothorax or prosoma, and the opisthosoma , or abdomen, and joined by a small, cylindrical pedicel . However, as there is currently neither paleontological nor embryological evidence that spiders ever had a separate thorax-like division, there exists an argument against the validity of the term cephalothorax, which means fused cephalon (head) and
8277-486: The vertical orientation of their fangs and the possession of four book lungs. Most, if not all, of the spiders one is likely to encounter in everyday life belong to infraorder Araneomorphae . It includes a wide range of spider families, including the orb-weaver spiders that weave their distinctive webs in gardens, the cobweb spiders that frequent window frames and the corners of rooms, the crab spiders that lurk on flowers waiting for nectar- and pollen-gathering insects,
8370-477: The very top level, there is broad agreement on the phylogeny and hence classification of spiders, which is summarized in the cladogram below. The three main clades into which spiders are divided are shown in bold; as of 2015 , they are usually treated as one suborder, Mesothelae , and two infraorders, Mygalomorphae and Araneomorphae , grouped into the suborder Opisthothelae . The Mesothelae, with about 140 species in 8 genera as of October 2020 , make up
8463-461: 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 torchlight reflected from
8556-497: Was described as herbivorous in 2008, but all other known species are predators , mostly preying on insects and other spiders, although a few large species also take birds and lizards. An estimated 25 million tons of spiders kill 400–800 million tons of prey every year. Spiders use numerous 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
8649-460: Was mistakenly administered to a S. grossa bite victim who was erroneously believed to have been bitten by the far more dangerous redback. (While the redback antivenom appears clinically active against arachnidism caused by Steatoda spiders, as these cases are often mild and the evidence of its effectiveness is limited, this treatment is not recommended.) They are not aggressive, and most injuries to humans are due to defensive bites delivered when
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