Overview

Comprehensive Description

AraneaeArachnidaArthropodaAnimalia

Araneae

  • Deltshev, Christo, Komnenov, Marjan, Blagoev, Gergin, Georgiev, Teodor, Lazarov, Stoyan, Stojkoska, Emilija, Naumova, Maria (2013): Faunistic diversity of spiders (Araneae) in Galichitsa mountain (FYR Macedonia). Biodiversity Data Journal 1, 977: 977-977, URL:http://dx.doi.org/10.3897/BDJ.1.e977
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AraneaeArachnidaArthropodaAnimalia

Araneae

  • Deltshev, Christo, Komnenov, Marjan, Blagoev, Gergin, Georgiev, Teodor, Lazarov, Stoyan, Stojkoska, Emilija, Naumova, Maria (2013): Faunistic diversity of spiders (Araneae) in Galichitsa mountain (FYR Macedonia). Biodiversity Data Journal 1, 977: 977-977, URL:http://dx.doi.org/10.3897/BDJ.1.e977
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Distribution

Geographic Range

Spiders are everywhere! Baby spiders are so light, they can put out a line of silk and float away on a breeze, and so they are spread around the globe. Also, spiders that live in peoples' houses often get moved around by accident when people move. Spiders are found on every continent, and there are over 40,000 species known to science. That's not all of them though, there are thousands more we don't know about yet.

Biogeographic Regions: nearctic (Native ); palearctic (Native ); oriental (Native ); ethiopian (Native ); neotropical (Native ); australian (Native ); oceanic islands (Native )

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Physical Description

Morphology

Physical Description

All spiders have two body sections: the cephalothorax in front and an abdomen behind. The abdomen contains the digestive and reproductive systems, and on the underside of it are the glands where silk is produced. The structures that produce the silk are called spinnerets.

They have eight legs, all attached to the cephalothorax. On the front of the cephalothorax are the mouth, the fangs, the eyes, and two small "mini-legs" called pedipalps. These are used to grab prey, and in mating, and are much bigger in male spiders than in females. Different species of spiders have six or eight eyes, and the size and arrangement of eyes is different in different groups. All spiders have fangs that they use to bite their prey with, and most have venom glands.

Female spiders are often much bigger than males.

Other Physical Features: bilateral symmetry

Sexual Dimorphism: female larger

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Ecology

Habitat

Spiders survive in every habitat on land except the very coldest. There are even a few in shallow fresh water.

Habitat Regions: temperate ; tropical

Terrestrial Biomes: tundra ; taiga ; desert or dune ; chaparral ; forest ; rainforest ; scrub forest ; mountains

Wetlands: marsh ; swamp ; bog

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Trophic Strategy

Food Habits

All spiders are predators. They attack only live Insecta, other Araneae, and other invertebrates. A few very large spider species attack small vertebrates like Squamata, Pimephales notatus, or Anura, but this is rare. Spiders are famous for trapping their prey in webs of sticky silk, but many of them are wandering predators who don't use silk to catch prey.

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Associations

Ecosystem Roles

Spiders are major predators of insects, including many insects that are pests to humans.

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Predation

Spiders often have good camouflage, and many of the wandering hunter species hunt at night when big predators can't see them. Many spiders build a retreat of silk to hide in too. Some are quick runners, and will just run away if they can. These may use their silk as a safety line, jumping off into the air with a silk thread attached so they don't fall.

Known Predators:

  • other Araneae 
  • Hymenoptera
  • Formicidae
  • praying mantids
  • Aves
  • small Squamata 
  • Amphibia
  • small mammals especially Soricidae 

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In Great Britain and/or Ireland:
Animal / predator / stocks nest with
female of Arachnospila anceps stocks nest with Araneae

Animal / predator / stocks nest with
female of Arachnospila consobrina stocks nest with Araneae

Animal / predator / stocks nest with
female of Arachnospila minutula stocks nest with Araneae

Animal / predator
Araneae is predator of Bombus

Animal / predator / stocks nest with
female of Auplopus carbonarius stocks nest with Araneae

Animal / pathogen
colony of Gibellula anamorph of Gibellula aranearum infects Araneae

Animal / pathogen
colony of Hymenostilbe anamorph of Hymenostilbe arachnophila infects Araneae

Animal / predator
larva of Melanophora roralis is predator of egg cocoon of Araneae

Animal / predator / stocks nest with
female of Miscophus ater stocks nest with Araneae

Animal / predator / stocks nest with
female of Miscophus concolor stocks nest with Araneae

Animal / predator
leaf of Pinguicula vulgaris is predator of adult of Araneae

Animal / parasitoid
gregarious, mycelioid perithecium of Torrubiella albolanata is parasitoid of Araneae

Animal / parasitoid
scattered, sparsely subiculate perithecium of Torrubiella aranicida is parasitoid of body & legs of Araneae

Animal / predator / stocks nest with
female of Trypoxylon attenuatum stocks nest with Araneae

Animal / predator / stocks nest with
female of Trypoxylon clavicerum stocks nest with Araneae

Animal / predator / stocks nest with
female of Trypoxylon figulus s.s. stocks nest with Araneae

Animal / predator / stocks nest with
female of Trypoxylon medium stocks nest with Araneae

Animal / predator / stocks nest with
female of Trypoxylon minus stocks nest with Araneae

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Known predators

Araneae is prey of:
Lagopus
Plectrophenax nivalis
Calidris maritima
Anura
Agelaius phoeniceus
Quiscalus quiscula
Melospiza melodia
Dendroica petechia
Geothlypis trichas
Empidonax minimus
Vireo gilvus
Icterus galbula
Pheucticus ludovicianus
Catharus fuscescens
Poecile atricapillus
Rana pipiens
Paridae
parasites
Aves
Lepidosauria
Hirundinidae
Scolopacidae
Talpinae
Aporosaura
Typhlosaurus
Red racer
Pituophis
Crotalus
Urocyon cinereoargenteus
Mephitinae
Onychomys
Geococcyx velox
Phasianidae
Timaliidae
Serpentes
Varanidae
Canis aureus
Erinaceus europaeus
bultul
Laniidae
Saxicoloides fulicata
Vulpes vulpes
Passeriformes
Calamospiza melanocorys
Peromyscus maniculatus
Orthoptera
Buteo jamaicensis
Saurothera vieilloti
Amphisbaena caeca
Herpestes auropunctatus
Eleutherodactylus coqui
Eleutherodactylus richmondi
Eleutherodactylus portoricensis
Eleutherodactylus wightmanae
Eleutherodactylus eneidae
Melanerpes portoricensis
Todus mexicanus
Mimocichla plumbea
Margarops fuscatus
Anolis cuvieri
Anolis evermanni
Anolis stratulus
Anolis gundlachi
Leptodactylus albilabris
Vireo latimeri
Nesospingus speculiferus
Icterus dominicensis
Mimetes portoricensis
Vireo altiloquus
Seiurus aurocapillus
Seiurus motacilla
Sphaerodactylus klauberi
Sphaerodactylus macrolepis
Diploglossus pleei
Geophilomorpha
Chlorostilbon maugeus
Anthracothorax viridis
Mniotilta varia
Parula americana
Dendroica caerulescens
Dendroica discolor
Setophaga ruticilla
Coereba flaveola
Loxigilla portoricensis
Pseudoscorpionida
Tyrannus dominicensis
Elaenia
Tiaris
Trochilidae
Anolis gingivinus
Anolis pogus
Chilopoda

Based on studies in:
Norway: Spitsbergen (Coastal)
Canada: Manitoba (Grassland)
Russia (Agricultural)
Malaysia (Swamp)
England: Oxfordshire, Wytham Wood (Forest)
Namibia, Namib Desert (Desert or dune)
USA: Alaska (Tundra)
USA: Arizona, Sonora Desert (Desert or dune)
India, Rajasthan Desert (Desert or dune)
USA: Massachusetts, Cape Ann (Marine)
USA: California, Cabrillo Point (Grassland)
Puerto Rico, El Verde (Rainforest)

This list may not be complete but is based on published studies.
  • N. N. Smirnov, Food cycles in sphagnous bogs, Hydrobiologia 17:175-182, from p. 179 (1961).
  • V. S. Summerhayes and C. S. Elton, Further contributions to the ecology of Spitzbergen, J. Ecol. 16:193-268, from p. 211 (1928).
  • V. S. Summerhayes and C. S. Elton, Further contributions to the ecology of Spitzbergen, J. Ecol. 16:193-268, from p. 217 (1928).
  • T. Mizuno and J. I. Furtado, Food chain. In: Tasek Bera, J. I. Furtado and S. Mori, Eds. (Junk, The Hague, Netherlands, 1982), pp. 357-359, from p. 358.
  • J. Brown, Ecological investigations of the Tundra biome in the Prudhoe Bay Region, Alaska, Special Report, no. 2, Biol. Pap. Univ. Alaska (1975), from p. xiv.
  • E. Holm and C. H. Scholtz, Structure and pattern of the Namib Desert dune ecosystem at Gobabeb, Madoqua 12(1):3-39, from p. 21 (1980).
  • R. W. Dexter, The marine communities of a tidal inlet at Cape Ann, Massachusetts: a study in bio-ecology, Ecol. Monogr. 17:263-294, from p. 288 (1947).
  • G. C. Varley, The concept of energy flow applied to a woodland community. In: Animal Populations in Relation to Their Food Resources, A. Watson, Ed. (Blackwell Scientific, Oxford, England, 1970), pp. 389-401, from p. 389.
  • V. S. Summerhayes and C. S. Elton, Contributions to the ecology of Spitsbergen and Bear Island, J. Ecol. 11:214-286, from p. 232 (1923).
  • R. D. Bird, Biotic communities of the Aspen Parkland of central Canada, Ecology, 11:356-442, from p. 410 (1930).
  • L. D. Harris and L. Paur, A quantitative food web analysis of a shortgrass community, Technical Report No. 154, Grassland Biome. U.S. International Biological Program (1972), from p. 17.
  • R. D. Bird, Biotic communities of the Aspen Parkland of central Canada, Ecology, 11:356-442, from p. 393 (1930).
  • R. D. Bird, Biotic communities of the Aspen Parkland of central Canada, Ecology, 11:356-442, from p. 406 (1930).
  • P. G. Howes, The Giant Cactus Forest and Its World: A Brief Biology of the Giant Cactus Forest of Our American Southwest (Duell, Sloan, and Pearce, New York; Little, Brown, Boston; 1954), from pp. 222-239, from p. 227.
  • R. D. Bird, Biotic communities of the Aspen Parkland of central Canada, Ecology, 11:356-442, from p. 383 (1930).
  • I. K. Sharma, A study of ecosystems of the Indian desert, Trans. Indian Soc. Desert Technol. and Univ. Center Desert Stud. 5(2):51-55, from p. 52 and A study of agro-ecosystems in the Indian desert, ibid. 5:77-82, from p. 79 1980).
  • Waide RB, Reagan WB (eds) (1996) The food web of a tropical rainforest. University of Chicago Press, Chicago
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Known prey organisms

Araneae preys on:
Prokelisia
Orchelimum
Acari
Diptera
Collembola
Insecta
Hemiptera
Pontania petiolaridis
Disyonicha quinquevitata
Nematocera imagines
Hymenoptera
Chironomidae
Achorutes
Scatophagidae
Reuteroscopus
Scaphytopius
Philaenus
Oecanthus
Empoasca
Lygus
Lepidoptera
Melanoplus
Orthoptera
Tenebrionidae
Curculionidae
Aclerda
Thysanura
Isoptera
Scarabaeidae
Pogonomyrmex
cactus weevils
Moneilema
Palo Verde weevil
Coleoptera
Auchenorrhyncha
Paracoenia turbida
herbivores
Empoasca fabae
black alate aphid
Anystis baccarum
Eleutherodactylus coqui
Eleutherodactylus richmondi
Eleutherodactylus portoricensis
Eleutherodactylus wightmanae
Eleutherodactylus eneidae
Eleutherodactylus hedricki
Sphaerodactylus klauberi
Sphaerodactylus macrolepis
Geophilomorpha
Schizomus
Sternorrhyncha
Thysanoptera
Formicidae
Orchelimum vulgare
Vanessa cardui
Mellisuga helenae
Misumena vatia

Based on studies in:
USA: Georgia (Marine)
Norway: Spitsbergen (Coastal)
England: Oxfordshire, Wytham Wood (Forest)
New Zealand (Grassland)
Puerto Rico, El Verde (Rainforest)
Canada: Manitoba (Grassland)
USA: Alaska (Tundra)
USA: Arizona, Sonora Desert (Desert or dune)
Malaysia (Swamp)
USA: Massachusetts, Cape Ann (Marine)
Russia (Agricultural)
India, Rajasthan Desert (Desert or dune)
USA: New Jersey (Agricultural)
Namibia, Namib Desert (Desert or dune)
USA: Yellowstone (Temporary pool)
USA: Illinois (Agricultural)

This list may not be complete but is based on published studies.
  • N. N. Smirnov, Food cycles in sphagnous bogs, Hydrobiologia 17:175-182, from p. 179 (1961).
  • V. S. Summerhayes and C. S. Elton, Further contributions to the ecology of Spitzbergen, J. Ecol. 16:193-268, from p. 211 (1928).
  • V. S. Summerhayes and C. S. Elton, Further contributions to the ecology of Spitzbergen, J. Ecol. 16:193-268, from p. 217 (1928).
  • T. Mizuno and J. I. Furtado, Food chain. In: Tasek Bera, J. I. Furtado and S. Mori, Eds. (Junk, The Hague, Netherlands, 1982), pp. 357-359, from p. 358.
  • D. J. Shure, Radionuclide tracer analysis of trophic relationships in an old-field ecosystem, Ecol. Monogr. 43(1):1-19, from p. 15 (1973).
  • J. Brown, Ecological investigations of the Tundra biome in the Prudhoe Bay Region, Alaska, Special Report, no. 2, Biol. Pap. Univ. Alaska (1975), from p. xiv.
  • E. Holm and C. H. Scholtz, Structure and pattern of the Namib Desert dune ecosystem at Gobabeb, Madoqua 12(1):3-39, from p. 21 (1980).
  • R. W. Dexter, The marine communities of a tidal inlet at Cape Ann, Massachusetts: a study in bio-ecology, Ecol. Monogr. 17:263-294, from p. 287 (1947).
  • R. W. Dexter, The marine communities of a tidal inlet at Cape Ann, Massachusetts: a study in bio-ecology, Ecol. Monogr. 17:263-294, from p. 288 (1947).
  • K. Paviour-Smith, The biotic community of a salt meadow in New Zealand, Trans. R. Soc. N.Z. 83(3):525-554, from p. 542 (1956).
  • G. C. Varley, The concept of energy flow applied to a woodland community. In: Animal Populations in Relation to Their Food Resources, A. Watson, Ed. (Blackwell Scientific, Oxford, England, 1970), pp. 389-401, from p. 389.
  • J. M. Teal, Energy flow in the salt marsh ecosystem of Georgia, Ecology 43(4):614-624, from p. 616 (1962).
  • V. S. Summerhayes and C. S. Elton, Contributions to the ecology of Spitsbergen and Bear Island, J. Ecol. 11:214-286, from p. 232 (1923).
  • R. D. Bird, Biotic communities of the Aspen Parkland of central Canada, Ecology, 11:356-442, from p. 410 (1930).
  • R. D. Bird, Biotic communities of the Aspen Parkland of central Canada, Ecology, 11:356-442, from p. 393 (1930).
  • R. D. Bird, Biotic communities of the Aspen Parkland of central Canada, Ecology, 11:356-442, from p. 406 (1930).
  • P. G. Howes, The Giant Cactus Forest and Its World: A Brief Biology of the Giant Cactus Forest of Our American Southwest (Duell, Sloan, and Pearce, New York; Little, Brown, Boston; 1954), from pp. 222-239, from p. 227.
  • R. D. Bird, Biotic communities of the Aspen Parkland of central Canada, Ecology, 11:356-442, from p. 383 (1930).
  • I. K. Sharma, A study of ecosystems of the Indian desert, Trans. Indian Soc. Desert Technol. and Univ. Center Desert Stud. 5(2):51-55, from p. 52 and A study of agro-ecosystems in the Indian desert, ibid. 5:77-82, from p. 79 1980).
  • M. A. Mayse and P. W. Price, 1978. Seasonal development of soybean arthropod communities in east central Illinois. Agro-Ecosys. 4:387-405, from p. 402.
  • M. A. Mayse and P. W. Price, 1978. Seasonal development of soybean arthropod communities in east central Illinois. Agro-Ecosys. 4:387-405, from p. 401.
  • N. C. Collins, R. Mitchell and R. G. Wiegert, Functional analysis of a thermal spring ecosystem, with an evaluation of the role of consumers, Ecology 57:1221-1232, from p. 1222 (1976).
  • Waide RB, Reagan WB (eds) (1996) The food web of a tropical rainforest. University of Chicago Press, Chicago
  • Myers, P., R. Espinosa, C. S. Parr, T. Jones, G. S. Hammond, and T. A. Dewey. 2006. The Animal Diversity Web (online). Accessed February 16, 2011 at http://animaldiversity.org. http://www.animaldiversity.org
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Life History and Behavior

Behavior

Communication and Perception

Spiders are very sensitive to vibrations, especially in their webs. Most don't see very well, but the Jumping Spiders see very well.

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Life Cycle

Development

Spiders hatch from eggs, and the hatchlings look more or less like grown-up spiders, though sometimes their colors change as they age. To grow they have to shed their exoskeleton, which they do many times during their lives. Unlike insects, some spider species keep growing after they become adults, and continue to molt as they get bigger.

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Life Expectancy

Lifespan/Longevity

Most spider species live a year or less, but some large ones can live for several years. Usually males die soon after they mate, it's only the females that can live longer.

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Reproduction

Mating System: monogamous ; polyandrous ; polygynous

After mating adult female spiders lay dozens to hundreds of eggs. The number varies among species and is affected by how well fed she is.

Breeding season: Spring to Fall, depending on the species and location.

Key Reproductive Features: semelparous ; iteroparous ; seasonal breeding ; sexual ; fertilization (Internal ); oviparous ; sperm-storing

Female spiders often guard their eggs and young, or even carry them with them until the young have hatched and molted.

Parental Investment: no parental involvement; female parental care

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Evolution and Systematics

Functional Adaptations

Functional adaptation

Web absorbs impacts: spiders
 

Webs of araneid spiders absorb impacts via microscopic engineering.

   
  This strategy inspired the web furniture system sketched by Linda Dong, a sophomore industrial design student at Carnegie Mellon University. "How can we create furniture using the least amount of material and manufacturing? The web is inspired by the strong and lightweight nature of spider webs. Using only tension from string, these pieces can hold their structure easily without additional glue or fasteners." Her sketch won the AskNature Student Design Sketch Competition on the basis of clear rendering, attention to product lifecycle and sustainability, and inspiration from nature (see Gallery).

"Spiders provide their nets with many microscopic engineering inventions to prepare the structure for the impact force of their prey or other intruders; webs of araneid spiders have several structural devices designed to absorb the impact energy without breaking the entire structure." (Pallasmaa 1995:81)

  Learn more about this functional adaptation.
  • Pallasmaa, J. 1995. Animal architecture. Helsinki: Museum of Finnish Architecture. 126 p.
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Functional adaptation

Silk used for various functions: spiders
 

Individual spiders are able to use silk for a variety of tasks by varying the properties of the silks they produce.

         
  "Certainly the most extraordinary material among those tabulated here is spider silk (that of silkworm moths is substantially less extreme)--it has the greatest tensile strength, astonishing extensibility, and by far the greatest strain energy storage…silks vary considerably in their properties, quite clearly tuned by natural selection to their particular tasks…A single araneid spider makes frame silk for the main members of its orb, viscid silk for the spiral threads that catch prey, cocoon silk, prey-wrapping silk, and so forth. Other kinds of spiders make other kinds of silks for other tasks…Spider silks do have an unusual combination of properties. But I know of no evidence that these can be achieved (if one wants them) only by a sequence-specific heteropolymer of amino acids, something unlikely to lend itself to cheap manufacture." (Vogel 2003:344-345)

Watch Video
  Learn more about this functional adaptation.
  • Steven Vogel. 2003. Comparative Biomechanics: Life's Physical World. Princeton: Princeton University Press. 580 p.
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Functional adaptation

Silk assembled on demand: spiders
 

Structural components of spider silk are safely stored and assembled on demand with help from a molecular switch.

       
  "Five times the tensile strength of steel and triple that of the  currently best synthetic fibers: Spider silk is a fascinating materialHow do spiders form long, highly stable and elastic fibers from the  spider silk proteins stored in the silk gland within split seconds?
 

"Spider silk consists of protein molecules, long chains comprising  thousands of amino-acid elements. X-ray structure analyses show that the  finished fiber has areas in which several protein chains are  interlinked via stable physical connections. These connections provide  the high stability. Between these connections are unlinked areas that  give the fibers their great elasticity.

 

"The situation within the silk gland is, however, very different: The  silk proteins are stored in high concentrations in an aqueous  environment, awaiting deployment. The areas responsible for interlinking  may not approach each other too closely; otherwise the proteins would  clump up instantaneously. Hence, these molecules must have some kind of  special storage configuration

 

"The protein chains are  stored with the polar areas on the outside and the hydrophobic parts of  the chain on the inside, ensuring good solubility in the aqueous  environment.

 

"When the protected proteins enter the spinning duct, they encounter  an environment with an entirely different salt concentration and  composition. This renders two salt bridges of the control domain  unstable, and the chain can unfold. Furthermore, the flow in the narrow  spinning duct results in strong shear forces. The long protein chains  are aligned in parallel, thus placing the areas responsible for  interlinking side by side. The stable spider silk fiber is formed.

 "'Our results have shown that the molecular switch we discovered at  the C-terminal end of the protein chain is decisive, both for safe  storage and for the fiber formation process,' says Franz Hagn." (Science Daily 2010)

  Learn more about this functional adaptation.
  • Hagn F; Eisoldt L; Hardy JG; Vendrely C; Coles M; Scheibel T; Kessler H. 2010. A conserved spider silk domain acts as a molecular switch that controls fibre assembly. Nature. 465: 239-242.
  • Rammensee S; Slotta U; Scheibel T; Bausch AR. 2008. Assembly mechanism of recombinant spider silk proteins. PNAS. 105(18): 6590-6595.
  • 2010. Investigating how spiders spin their silk, researchers unravel a key step. Science Daily [Internet],
  • Minkel JR. 2008. Researchers Build Micro Spider-Silk Spinner. Scientific American [Internet],
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Functional adaptation

Legs detect airborne vibrations: spiders
 

The legs of some spiders detect airborne vibrations of approaching insects thanks to specialized vibration-sensitive hairs, called trichobothria, on certain leg segments.

     
  "Spiders can detect vibrations traveling through the air from sources far away. They can do this thanks to specialized vibration-sensitive hairs, called trichobothria, on certain segments of their limbs. These hairs are able to move in any direction, and tell the spider the direction from which an object is approaching and its size. They are so responsive to airborne vibrations that they can deven detect those caused by the wings of insects in flight, alerting the spider to the approach of a potential victim as it heads toward the spider's web." (Shuker 2001:36)
  Learn more about this functional adaptation.
  • Shuker, KPN. 2001. The Hidden Powers of Animals: Uncovering the Secrets of Nature. London: Marshall Editions Ltd. 240 p.
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Functional adaptation

Legs use hydraulics: spiders
 

Legs of spiders extend by hydraulic pressure of built-up fluids.

   
  "A remarkable and effective hydraulic mechanism is found in the legs of spiders, which have muscles to flex the joints but none to extend them. Spiders stretch their legs by pumping fluid into them. When a spider gets ready to jump, it generates, for a fraction of a second, excess pressure of up to 60 percent of an atmosphere. The legs extend in order to accommodate more fluid." (Tributsch 1984:59)

"One particular hydraulic device is worth a little more attention here, partly because its existence comes as yet another surprise and partly because it achieves antagonism for contractile muscle in an unusual way. The eight legs of a spider differ little from the six of an insect, but a curious special feature of spider legs has been known for almost a century. While properly equipped with flexor muscles (ones that decrease the angle between one segment and another), they lack the antagonistic extensor muscles (ones that increase that angle toward 180 degrees). Biologists casually assumed that elasticity of the interarticular membranes provided the antagonistic force, not on the face of it an unreasonable idea. But Ellis (1944) remembered that spiders die with legs severely flexed. If elasticity did the extension, they would more likely die with legs extended or at least not so flexed--as do insects. He found that cutting off the tip of a leg prevented reextenson until the tip was resealed; and he found that mild exsanguination reduced a spider's ability to extend any of its legs. He suggested that extension in spider legs was hydraulic, not muscular or elastic. The idea was confirmed by Parry and Brown (1959), who measured resting pressures of 6.6 kilopascals and transient pressures of up to 60 kilopascals (over half an atmosphere) in spider legs. An isolated leg could lift more weight as the pressure inside it was increased, and the spiders turned out to have a special mechanism to seal off a joint that prevented fatal depressurization when a leg was lost." (Vogel 2003:421)
  Learn more about this functional adaptation.
  • Steven Vogel. 2003. Comparative Biomechanics: Life's Physical World. Princeton: Princeton University Press. 580 p.
  • Tributsch, H. 1984. How life learned to live. Cambridge, MA: The MIT Press. 218 p.
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Functional adaptation

Silk tricks insects: spiders
 

The webs of some spiders trick and catch prey via UV-colored silk.

   
  "But while UV vision helps many species of insect, it can also be used to trick them. Several species of spider, for example, include UV-colored sheets of silk in their webs, which insects mistake for nectar guides or for escape routes from dense vegetation, only to be lethally snared by the web's sticky coating." (Shuker 2001:21)
  Learn more about this functional adaptation.
  • Shuker, KPN. 2001. The Hidden Powers of Animals: Uncovering the Secrets of Nature. London: Marshall Editions Ltd. 240 p.
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Functional adaptation

Mechanism to seal joint prevents depressurization: spiders
 

The legs of spiders are protected from depressurization when damaged via a joint sealing mechanism.

   
  "One particular hydraulic device is worth a little more attention here, partly because its existence comes as yet another surprise and partly because it achieves antagonism for contractile muscle in an unusual way. The eight legs of a spider differ little from the six of an insect, but a curious special feature of spider legs has been known for almost a century. While properly equipped with flexor muscles (ones that decrease the angle between one segment and another), they lack the antagonistic extensor muscles (ones that increase that angle toward 180 degrees). Biologists casually assumed that elasticity of the interarticular membranes provided the antagonistic force, not on the face of it an unreasonable idea. But Ellis (1944) remembered that spiders die with legs severely flexed. If elasticity did the extension, they would more likely die with legs extended or at least not so flexed--as do insects. He found that cutting off the tip of a leg prevented re-extenson until the tip was resealed; and he found that mild exsanguination reduced a spider's ability to extend any of its legs. He suggested that extension in spider legs was hydraulic, not muscular or elastic. The idea was confirmed by Parry and Brown (1959), who measured resting pressures of 6.6 kilopascals and transient pressures of up to 60 kilopascals (over half an atmosphere) in spider legs. An isolated leg could lift more weight as the pressure inside it was increased, and the spiders turned out to have a special mechanism to seal off a joint that prevented fatal depressurization when a leg was lost." (Vogel 2003:421)
  Learn more about this functional adaptation.
  • Steven Vogel. 2003. Comparative Biomechanics: Life's Physical World. Princeton: Princeton University Press. 580 p.
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Molecular Biology and Genetics

Molecular Biology

Statistics of barcoding coverage

Barcode of Life Data Systems (BOLD) Stats
Specimen Records: 78673
Specimens with Sequences: 59389
Specimens with Barcodes: 56807
Species: 4914
Species With Barcodes: 4315
Public Records: 52306
Public Species: 2026
Public BINs: 6464
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Barcode data

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Relevance to Humans and Ecosystems

Benefits

Economic Importance for Humans: Negative

Spiders scare a lot of people (usually this is unnecessary). A few spider species have venom that is dangerous to people, but spider bites are actually pretty rare. They get blamed for a lot of skin injuries that are not actually spider bites. Most spiders have such small weak fangs that they couldn't break a person's skin, even if they wanted to.

Negative Impacts: injures humans (bites or stings)

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Economic Importance for Humans: Positive

Spiders eat a lot of insects that are agricultural pests and eat our food.

Positive Impacts: controls pest population

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