Spider
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| Spider | |||||||||
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| Orb weaver spider (family: Araneidae) | |||||||||
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| 111 families, 40,000 species | |||||||||
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Spiders are invertebrate arachnids. They have eight legs, and make silk. Spiders are the biggest group in arachnids, after Acarina, the mites and ticks. Some spiders are smaller than a coin and some are so big they eat small birds. Most spiders eat insects. They catch the insects either by building a spider web, or by using a thread of silk they throw at the insect. Sometimes they hide in holes in the ground, then run out and grab an insect that walks by. Or they will make web "nets" to catch passing insects. Or they will even go out and attack them with no webs at all. Spiders do not have wings. Some can also jump quite well.
Very few spiders are dangerous to humans. They have fangs (pointy teeth) that they use to bite people and put poison in them. The poison usually causes pain. The poison of a few spiders can kill a person.
Being afraid of spiders is a very common fear.
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[change] Some spiders are not predators
Most spiders are predators, but the jumping spider Bagheera kiplingi gets over 90% of its food from fairly solid plant material produced by acacias as part of a mutually beneficial relationship with a species of ant.[1]
Young spiders of the families Anyphaenidae, Corinnidae, Clubionidae, Thomisidae and Salticidae feed on plant nectar. Studies have shown that they do this on purpose and for long time periods. They also clean themselves periodically while feeding. These spiders also prefer sugar solutions to plain water, which shows that they are looking for nutritients. Many spiders are nocturnal, they are most active during the night. The extent of nectar consumption by spiders may therefore have been under-estimated. Nectar contains amino acids, lipids, vitamins and minerals in addition to sugars. Studies have shown that other spider species live longer when nectar is available. Feeding on nectar also avoids the risks of struggles with prey, and the costs of producing venom and digestive enzymes.[2]
Various species are known to feed on dead arthropods (scavenging), web silk, and their own shed exoskeletons. Pollen caught in webs may also be eaten, and studies have shown that young spiders have a better chance of survival if they have the opportunity to eat pollen. In captivity, several spider species are also known to feed on bananas, marmalade, milk, egg yolk and sausages.[2] In one praying mantis species, young spiders also actively feed on pollen and adults that capture pollen-laden insects eat the pollen as well.[3]
[change] Methods of catching prey
Most spiders are predators, they capture prey. The best-known method how spiders capture prey is by using a sticky web. The placement of the web allows different spiders to trap different insects in the same area. Flat, horizontal webs allow them to trap insects that fly up from vegetation underneath, for example. Flat vertical nets allow them to trap insects in flight. The spiders that build webs usually don't see very well, but they are very sensitive to vibrations.[4]
Females of the water spider Argyroneta aquatica build underwater "diving bell" webs which they fill with air and use for digesting prey, molting, mating and raising offspring. They live almost entirely within the bells, darting out to catch prey animals that touch the bell or the threads that anchor it. [5] A few spiders use the surfaces of lakes and ponds as "webs", detecting trapped insects by the vibrations that these cause while struggling.[4]
Net-casting spiders weave only small webs but then manipulate them to trap prey. Those of the genus Hyptiotes and the family Theridiosomatidae stretch their webs and then release them when prey strike them, but do not actively move their webs. Those of the family Deinopidae weave even smaller webs, hold them outstretched between their first two pairs of legs, and lunge and push the webs as much as twice their own body length to trap prey, and this move may increase the webs' area by a factor of up to ten. Experiments have shown that Deinopis spinosus has two different techniques for trapping prey: backwards strikes to catch flying insects, whose vibrations it detects; and forward strikes to catch ground-walking prey that it sees. These two techniques have also been observed in other deinopids. Walking insects form most of the prey of most deinopids, but one population of Deinopis subrufus appears to live mainly on tipulid flies that they catch with the backwards strike.[6]
Mature female bolas spiders of the genus Mastophora build "webs" that consist of only a single "trapeze line", which they patrol. They also construct a bolas made of a single thread, tipped with a large ball of very wet sticky silk. They emit chemicals that resemble the pheromones of moths, and then swing the bolas at the moths. Although they miss on about 50% of strikes, they catch about the same weight of insects per night as web-weaving spiders of similar size. The spiders eat the bolas if they have not made a kill in about 30 minutes, rest for a while, and then make new bolas.[7][8] Juveniles and adult males are much smaller and do not make bolas. Instead they release different pheromones that attract moth flies, and catch them with their front pairs of legs.[9]
[change] Using Trapdoors
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The primitive Liphistiidae, the "trapdoor spiders" (family Ctenizidae) and many tarantulas are ambush predators that lurk in burrows, often closed by trapdoors and often surrounded by networks of silk threads that alert these spiders to the presence of prey.[10] Other ambush predators do without such aids, including many crab spiders,[4] and a few species that prey on bees, which see ultraviolet, can adjust their ultraviolet reflectance to match the flowers in which they are lurking.[11] Wolf spiders, jumping spiders, fishing spiders and some crab spiders capture prey by chasing it, and rely mainly on vision to locate prey.[4]
[change] Hunting other spiders
Some jumping spiders of the genus Portia hunt other spiders in ways that seem intelligent,[13] outflanking their victims or luring them from their webs. Laboratory studies show that Portia's instinctive tactics are only starting points for a trial-and-error approach from which these spiders learn very quickly how to overcome new prey species.[12] However they seem to be relatively slow "thinkers", which is not surprising as their brains are vastly smaller than those of mammalian predators[13]
[change] Disguising as ants
Ant-mimicking spiders face several challenges: they generally develop slimmer abdomens and false "waists" in the cephalothorax to mimic the three distinct regions (tagmata) of an ant's body; they wave the first pair of legs in form to their heads to mimic antennae, which spiders lack, and to conceal the fact that they have but eight legs rather than six; they develop large color patches round one pair of eyes to disguise the fact that they generally have eight simple eyes, while ants have two compound eyes; they cover their bodies with reflective hairs to resemble the shiny bodies of ants. In some spider species males and females mimic different ant species, as female spiders are usually much larger than males. Ant-mimicking spiders also modify their behavior to resemble that of the target species of ant, for example many adopt a zig-zag pattern of movement, ant-mimicking jumping spiders avoid jumping, and spiders of the genus Synemosyna walk on the outer edges of leaves in the same way as Pseudomyrmex. Ant-mimicry in many spiders and other arthropods may be for protection from predators that hunt by sight, including birds, lizards and spiders. However several ant-mimicking spiders prey either on ants or on the ants "livestock" such as aphids. When at rest the ant-mimicking crab spider Amyciaea does not closely resemble Oecophylla, but while hunting it imitates the behavior of a dying ant to attract worker ants. After a kill some ant-mimicking spiders hold their victims between themselves and large groups of ants to avoid being attacked.[14]
[change] Spiders and humans
Of the 40.000 spiders, less than 12 are known to be dangerous to humans. Most of the time, being bitten by a spider is painful. Most spiders use poison to paralyse their prey; they kill it through eating, or through a bite. A few spiders have poisons that can be dangerous to weakened people and those allergic to it. Since 1927, 13 people have died, after a bite Atrax robustus, a spider from Australia.
[change] References
- ↑ Meehan, C,J. Olson, E.J. and Curry, R.L. (21 August 2008), Exploitation of the Pseudomyrmex–Acacia mutualism by a predominantly vegetarian jumping spider (Bagheera kiplingi). Retrieved on 2008-10-10
- ↑ 2.0 2.1 Jackson, R.R. et al. (2001). "Jumping spiders (Araneae: Salticidae) that feed on nectar" (PDF). J. Zool. Lond. 255: 25–29. DOI:10.1017/S095283690100108X.
- ↑ Beckman, N. and Hurd, L.E. (August 2003). "Pollen Feeding and Fitness in Praying Mantids: The Vegetarian Side of a Tritrophic Predator". Environmental Entomology 32 (4): 881–885. DOI:[0881:PFAFIP2.0.CO;2 10.1603/0046-225X(2003)032[0881:PFAFIP]2.0.CO;2].
- ↑ 4.0 4.1 4.2 4.3 Ruppert, E.E., Fox, R.S., and Barnes, R.D. (2004). Invertebrate Zoology, 7, Brooks / Cole, 571–584. ISBN 0030259827.
- ↑ Schütz, D., and Taborsky, M. (2003). "Adaptations to an aquatic life may be responsible for the reversed sexual size dimorphism in the water spider, Argyroneta aquatica" (PDF). Evolutionary Ecology Research 5 (1): 105–117. Retrieved on 11 October 2008.
- ↑ Coddington, J., and Sobrevila, C. (1987). "Web manipulation and two stereotyped attack behaviors in the ogre-faced spider Deinopis spinosus Marx (Araneae, Deinopidae)." (PDF). Journal of Arachnology 15: 213–225. Retrieved on 11 October 2008.
- ↑ Eberhard, W.G. (December 1977). "Aggressive Chemical Mimicry by a Bolas Spider" (PDF). Science 198 (4322): 1173–1175. DOI:10.1126/science.198.4322.1173. Retrieved on 10 October 2008.
- ↑ Eberhard, W.G. (1980). "The Natural History and Behavior of the Bolas Spider, Mastophora dizzydeani sp. n. (Araneae)". Psyche 87: 143–170. Retrieved on 10 October 2008.
- ↑ Yeargan, K.V., and Quate, L.W. (1997). "Adult male bolas spiders retain juvenile hunting tactics". Oecologia 112 (4): 572–576. DOI:10.1007/s004420050347.
- ↑ Coddington, J.A. & Levi, H.W. (1991). "Systematics and Evolution of Spiders (Araneae)". Annu. Rev. Ecol. Syst. 22: 565–592. DOI:10.1146/annurev.es.22.110191.003025.
- ↑ Oxford, G.S. & Gillespie, R.G. (1998). Evolution and Ecology of Spider Coloration. Annual Review of Entomology 43:619-643. Template:DOI
- ↑ 12.0 12.1 Wilcox, S. and Jackson, R. (2002). "Jumping Spider Tricksters", in Bekoff, M., Allen, C., and Burghardt, G.M.: The Cognitive Animal: Empirical and Theoretical Perspectives on Animal Cognition. MIT Press, 27–34. ISBN 0262523221.
- ↑ 13.0 13.1 Harland, D.P., and Jackson, R.R. (2000). "PDF “Eight-legged cats” and how they see - a review of recent research on jumping spiders (Araneae: Salticidae)". Cimbebasia 16: 231–240. Retrieved on 11 October 2008.
- ↑ Mclver, J.D. and Stonedahl, G. (January 1993). "Myrmecomorphy: Morphological and Behavioral Mimicry of Ants". Annual Review of Entomology 38: 351–377. DOI:10.1146/annurev.en.38.010193.002031.
