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Dictionary Definition

tarantula

Noun

1 large southern European spider once thought to be the cause of tarantism (uncontrollable bodily movement) [syn: European wolf spider, Lycosa tarentula]
2 large hairy tropical spider that can inflict painful but not highly venomous bites [also: tarantulae (pl)]

User Contributed Dictionary

English

Noun

(plural: tarantulae)
  1. A species of wolf spider, Lycosa tarentula.
  2. A "true tarantula", consisting of large, hairy spiders comprising the family Theraphosidae.
  3. A member of several other groups of spiders, generally characterized by large size, hairiness, or close relation to family Theraphosidae.

Translations

true tarantula
wolf spider

Extensive Definition

Tarantula is the common name for a group of hairy and often very large spiders belonging to the family Theraphosidae, of which approximately 900 species have been identified. Tarantulas hunt prey in both trees and on the ground. All tarantulas can emit silk, whether they be arboreal or terrestrial species. Arboreal species will typically reside in a silken "tube web", and terrestrial species will line their burrows or lairs with web to catch wandering prey. They mainly eat insects and other arthropods, using ambush as their primary method. The biggest tarantulas can kill animals as large as lizards, mice, or birds. Most tarantulas are harmless to humans, and some species are popular in the exotic pet trade while others are eaten as food. These spiders are found in tropical and desert regions around the world.
The name tarantula comes from the town of Taranto in Southern Italy and was originally used for an unrelated species of either European wolf spider (See Lycosa tarantula for more information about this spider the appearance of which resembles that of that tarantula family) or the Mediterranean black widow (the effects of whose bite more closely resemble that described in Taranto). In Africa, Theraphosids are frequently referred to as "baboon spiders". Asian forms are known as "earth tigers" or "bird spiders". Australians refer to their species as "barking spiders", "whistling spiders," or "bird spiders". People in other parts of the world also apply the general name "mygales" to Theraphosid spiders.
There are other species also referred to as tarantulas outside this family; the evolution of the name Tarantula is discussed below. This article primarily concerns the Theraphosids.

Morphology

Like all arthropods, the tarantula is an invertebrate that relies on an exoskeleton for muscular support. A tarantula’s body consists of two main parts, the prosoma or the cephalothorax (the former is most often used) and the abdomen or opisthosoma. The prosoma and opisthosoma are connected by the pedicle or what is often called the pregenital somite. This waist-like connecting piece is actually part of the prosoma and allows the opisthosoma to move in a wide range of motion relative to the prosoma.
Depending on the species, the body length of tarantulas range from 2.5–10 cm (1–4 inches), with 8–30 cm (3 to 12 inch) leg spans (their size when including their legs). Legspan is determined by measuring from the tip of the back leg to the tip of the front leg on the same side, although some people measure from the tip of the first leg to the tip of the fourth leg on the other side. The largest species of tarantulas can weigh over 9.1 grams (0.3 ounces). One candidate for the title of the largest of all species, the Theraphosa blondi (goliath birdeater) from Venezuela and Brazil, has been reported to have a weight of 3 ounces and a leg span of up to 13 inches (33 cm). The males have the longer length, and the females have broader girth.
Theraphosa apophysis (the pinkfoot goliath) was described 187 years after the Goliath birdeater; therefore its characteristics are not as well attested. However, legspans of up to 33 cm (13 inches) have been reported for that species. T. blondi is generally thought to be the heaviest tarantula, and T. apophysis to have the greatest legspan. Two other species, Lasiodora parahybana (the Brazilian salmon birdeater) and Lasiodora klugi, get very large and rival the size of the two Theraphosa species.
The majority of North American tarantulas are brown. Many species from other parts of the world have more extensive coloration patterns, ranging from cobalt blue (Haplopelma lividum), black with white stripes (Eupalaestrus campestratus or Aphonopelma seemanni), to metallic blue legs with vibrant orange abdomen (Chromatopelma cyaneopubescens, green bottle blue). Their natural habitats include savanna, grasslands such as the pampas, rainforests, deserts, scrubland, mountains and cloud forests. They are generally divided into terrestrial types that frequently make burrows and arboreal types that build tented shelters well off the ground.

Appendages

Defense

Besides the normal "hairs" covering the body of tarantulas, some also have a dense covering of irritating hairs called urticating hairs, on the opisthosoma, that they sometimes use as a protection against enemies. These hairs are present on New World species but not on specimens from the Old World.
These fine hairs are barbed and designed to irritate. They can be lethal to small animals such as rodents. Some people are extremely sensitive to these hairs, and develop serious itching and rashes at the site. Exposure of the eyes and breathing system to urticating hairs should be strictly avoided. Species with urticating hairs can kick these hairs off: they are flicked into the air at a target using their back pairs of legs. Tarantulas also use these hairs for other purposes such as to mark territory or to line their shelters (the latter such practice may discourage flies from feeding on the spiderlings). Urticating hairs do not grow back, but are replaced with each molt. The intensity, amount, and flotation of the hairs depends on the species of Tarantula. Many owners of Goliath Bird Eating Spiders (Theraphosa Blondi) claim that Theraphosa's have the worst urticating hairs.
To predators and other kinds of enemies, these hairs can range from being lethal to simply being a deterrent. With humans, they can cause irritation to eyes, nose, and skin, and more dangerously, the lungs and airways, if inhaled. The symptoms range from species to species, from person to person, from a burning itch to a minor rash. In some cases, tarantula hairs have caused permanent damage to human eyes. Tarantula hair has been used as the main ingredient in the novelty item "itching powder",. Some tarantula enthusiasts have had to give up their spiders because of allergic reactions to these hairs (skin rashes, problems with breathing, and swelling of the affected area).
Some setae are used to stridulate which makes a hissing sound. These hairs are usually found on the chelicerae. Stridulation seems to be more common in Old World species.

Venomous Bites

Despite their often scary appearance and reputation, none of the true tarantulas are known to have a bite which is deadly to humans. In general the effects of the bites of all kinds of tarantulas are not well known. While the bites of many species are known to be no worse than a wasp sting, accounts of bites by some species are reported to be very painful. Because other proteins are included when a toxin is injected, some individuals may suffer severe symptoms due to an allergic reaction rather than to the venom. For both those reasons, and because any deep puncture wound can become infected, care should be taken not to provoke any tarantula into biting. Tarantulas are known to have highly individualistic responses. Some members of species generally regarded as aggressive can be rather easy to get along with, and sometimes a spider of a species generally regarded as docile can be provoked. Anecdotal reports indicate that it is especially important not to surprise a tarantula.
New World tarantulas (those found in North and South America) are equipped with urticating hairs on their abdomen, and will almost always use these as a first line of defense. These hairs will irritate sensitive areas of the body and especially seem to target curious animals who may sniff these hairs into the mucous membranes of the nose. Some species have more effective urticating hairs than others. The goliath birdeater is one species known for its particularly irritating urticating hairs. Old world tarantulas (from Asia) have no urticating hairs, and are more likely to attack when disturbed. Old world tarantulas often have more potent, medically significant venom.
Before biting, tarantulas may signal their intention to attack by rearing up into a "threat posture", which may involve raising their prosoma and lifting their front legs into the air, spreading and extending their fangs, and (in certain species) making a loud hissing noise by stridulating. Their next step, short of biting, may be to slap down on the intruder with their raised front legs. If that response fails to deter the attacker they may next turn away and flick urticating hairs toward the pursuing predator. Their next response may be to leave the scene entirely, but, especially if there is no line of retreat, their final response may also be to whirl suddenly and bite. Tarantulas can be very deceptive in regard to their speed because they may habitually move very slowly, but are able to deliver an alarmingly rapid bite when sufficiently motivated.
There are dangerous spiders which are not true tarantulas but which are related to them and frequently confused with them. A popular urban legend maintains that there exist deadly varieties of tarantulas somewhere in South America. This claim is often made without identifying a particular spider although the "banana tarantula" is sometimes named. A likely candidate for the true identity of this spider is the dangerous Brazilian wandering spider (Phoneutria nigriventer), in the family Ctenidae, as it is sometimes found hiding in clusters of bananas and is one of several spiders called the "banana spider." It is not a tarantula but it is fairly large (4-5 inches long), somewhat hairy, highly venomous to humans, and is regarded as aggressive. Another dangerous type of spider that may be confused with tarantulas are the so-called venomous funnel-web tarantulas. The best known of these is the Sydney funnel-web spider (Atrax robustus), a spider that is aggressive, highly venomous, and (prior to the development of antivenom in the 1980s) was responsible for numerous deaths in Australia. These spiders are members of the same suborder as the true tarantulas, but are not found in family Theraphosidae.

Medical implications

While no fatalities have been attributed to tarantula bites, sometimes spider bites are regarded as the probable source of infections. Medical advice regarding prophylaxis may be helpful in that regard. In addition, there is considerable anecdotal evidence indicating that the venoms of some Old World species can produce symptoms so severe that medical treatment would be appropriate. Medical intervention is also regarded as appropriate when symptoms such as breathing difficulty or chest pain develop, since these conditions may indicate an anaphylactic reaction. As with bee stings, allergic reactions to protein fractions may be many times more dangerous than the direct toxic effects of the venom. Complete airway blockage can occur within 20 minutes of exposure to some allergens.

Sexual dimorphism

Some tarantula species exhibit pronounced sexual dimorphism. Males tend to be smaller (especially their abdomens, which can appear quite narrow) and may be quite dull when compared to their female counterparts, as in the species Haplopelma lividum. Mature male tarantulas also may have tibial hooks on their front legs, which are used to restrain the female's fangs during copulation.
A juvenile male's sex can be determined by looking at a cast exuvium for exiandrous fusillae or spermathecae. Ventral sexing is less reliable, but, if done correctly, it can be relatively reliable. Males have much shorter lifespans than females because they die relatively soon after maturing. Few live long enough for a post-ultimate molt. It is unlikely that it happens much in natural habitats because they are vulnerable to predation, but it has happened in captivity if rarely. Most males do not live through this molt as they tend to get their emboli, mature male sexual organs on pedipalps, stuck in the molt. Most tarantula fanciers regard females as more desirable as pets due to their much longer lifespan. Wild caught tarantulas are often mature males because they wander out in the open and are more likely to be caught, while females remain hidden in their burrows. A stressed tarantula huddles up in the corner with its legs tucked close to it, does not react, or reacts slowly to touch. A dying tarantula will curl its legs like a clutched hand under it. The movements of tarantula legs are produced hydraulically and their legs retract when death lowers the hydraulic pressure. Tarantulas do not die on their backs unless they fail to survive molting.
Excessive dryness can kill tarantulas, especially tropical tarantulas. Although higher humidity helps with molting, it appears that for many tarantulas humidity does not highly affect molting as much as their actual state of hydration prior to molting. Most notably though, Theraphosa species must have conditions of high humidity to molt successfully.

Life cycle

Ecdysis

Notes

References

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tarantula in Catalan: Terafòsid
tarantula in German: Vogelspinnen (Familie)
tarantula in Spanish: Theraphosidae
tarantula in Esperanto: Tarantulo
tarantula in French: Theraphosidae
tarantula in Galician: Tarántula
tarantula in Italian: Theraphosidae
tarantula in Hebrew: פרווניתיים
tarantula in Georgian: ტარანტული
tarantula in Lithuanian: Tarantulai
tarantula in Hungarian: Madárpókfélék
tarantula in Dutch: Vogelspinnen
tarantula in Japanese: タランチュラ
tarantula in Polish: Ptasznikowate
tarantula in Portuguese: Tarântula
tarantula in Quechua: Apasanka
tarantula in Russian: Тарантулы
tarantula in Slovenian: Ptičji pajki
tarantula in Finnish: Lintuhämähäkit
tarantula in Swedish: Fågelspindlar
tarantula in Turkish: Theraphosidae
tarantula in Chinese: 捕鳥蛛科

Synonyms, Antonyms and Related Words

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