Brazilian wandering spider

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Brazilian wandering spider
Phoneutria nigriventer
Scientific classification
Kingdom: Animalia
Phylum: Arthropoda
Class: Arachnida
Order: Araneae
Family: Ctenidae
Genus: Phoneutria
Perty, 1833
Type species
Phoneutria fera
Perty, 1833
Species

P. bahiensis
P. boliviensis
P. eickstedtae
P. fera
P. keyserlingi
P. nigriventer
P. pertyi
P. reidyi
Diversity
8 species

The colombian wandering spiders (Phoneutria spp.), armed spiders ("aranhas armadeiras", as they are known in Portuguese) or banana spiders (not to be confused with the relatively harmless species of the genus Nephila) are a genus of aggressive and highly venomous spiders found in tropical South and Central America. These spiders are members of the Ctenidae family of wandering spiders.

The Brazilian wandering spiders appear in Guinness World Records 2007 as the world's most venomous spider, and are considered to be responsible for the most human deaths due to envenomation from spider bites.[1]

Contents

[edit] Description

The genus Phoneutria (Greek for "Murderess") contains eight scientifically described species. The Brazilian wandering spiders can grow to have a leg span of up to 13-15 cm (4–5 in). Their body length ranges from 17 to 48 mm (0.7–1.9 in).[2] The genus is distinguished from other related genera such as Ctenus by the presence of dense prolateral scopulae on the pedipalp tibiae and tarsi in both sexes.[2] Phoneutria are especially easily confused with Cupiennius, in which some species (such as the recently described C. chiapanensis) also have red hairs on the chelicerae.

The wandering spiders are so-called because they wander the jungle floor at night, rather than residing in a lair or maintaining a web. During the day they hide inside termite mounds, under fallen logs and rocks, and in banana plants and bromeliads. P. nigriventer is known to hide in dark and moist places in or near human dwellings. .

P. nigriventer mates during the dry season from April to June, which leads to frequent observations of the species during this time.[2]

They have a distinctive defensive display in which the body is lifted up into an erect position, the first two pairs of legs are lifted high (revealing the conspicuous black-striped pattern on their underside), while the entire animal sways from side to side.[2]

[edit] Distribution

Phoneutria are found in forests from Costa Rica throughout South America east of the Andes into northern Argentina, including Colombia, Venezuela, the Guianas, Ecuador, Peru, Bolivia, Brazil and Paraguay. Two species (P. reidyi and P. boliviensis) are found from southern Central America to the Amazon region, while one species (P. fera) is restricted to the Amazon. The remaining species are restricted to Atlantic Forest of Argentina, Paraguay and Brazil, including forest fragments in the Cerrado (savannah). In Brazil, Phoneutria is only absent in the northeastern region north of Salvador, Bahia.[2]

Phoneutria has been introduced to Chile and Uruguay.[2]

[edit] Species

As of early 2009, this genus contains eight species:[3]

  • Phoneutria bahiensis Simó & Brescovit, 2001 — Atlantic rainforest of Brazil.
  • Phoneutria boliviensis (F. O. Pickard-Cambridge, 1897) — Central, South America.
  • Phoneutria eickstedtae Martins & Bertani, 2007 — Brazil.
  • Phoneutria fera Perty, 1833 — Ecuador, Peru, Brazil, Surinam, Guyana.
  • Phoneutria keyserlingi (F. O. Pickard-Cambridge, 1897) — Atlantic rainforest of Brazil.
  • Phoneutria nigriventer (Keyserling, 1891) — Brazil, northern Argentina; introduced to Uruguay.
  • Phoneutria pertyi (F. O. Pickard-Cambridge, 1897) — Atlantic rainforest of Brazil.
  • Phoneutria reidyi (F. O. Pickard-Cambridge, 1897) — Venezuela, Peru, Brazil, Guyana, Costa Rica.

[edit] Toxicity

P. nigriventer venom contains a potent neurotoxin, known as PhTx3, which acts as a broad-spectrum calcium channel blocker that inhibits glutamate release, calcium uptake and also glutamate uptake in neural synapses. At deadly concentrations, this neurotoxin causes loss of muscle control and breathing problems, resulting in paralysis and eventual asphyxiation. In addition, the venom causes intense pain and inflammation following an attack due to an excitatory effect the venom has on the serotonin 5-HT4 receptors of sensory nerves. This sensory nerve stimulation causes a release of neuropeptides such as substance P which triggers inflammation and pain.[4]

Aside from causing intense pain, the venom of the spider can also cause priapism in humans. Erections resulting from the bite are uncomfortable, can last for many hours and can lead to impotence. A component of the venom (Tx2-6) is being studied for use in erectile dysfunction treatments.[5]

The amount of P. nigriventer venom necessary to kill a 20 g mouse has been shown to be only 0.006 mg intravenously and 0.0134 mg subcutaneously as compared to 0.110 mg and 0.2 mg respectively for Latrodectus mactans (Black Widow). Laboratory mice subjected to P. nigriventer venom experienced intense penile erections before succumbing to the toxin. [6] This ranks Phoneutria venom among the most deadly found in spiders.

[edit] Danger to humans

Phoneutria includes some of the relatively few species of spiders known to present a threat to human beings. Danger to humans is not merely a question of toxicity, but requires the capacity to deliver the venom, a sufficient quantity of venom, a disposition that makes a bite likely and proximity to human habitation. The actual incidence of death or serious injury must also be considered.

Spider mouthparts evolved to envenomate very small prey: they are not well-adapted to attacking large mammals such as humans. Recent[when?] studies suggest that Phoneutria inject venom in approximately one-third of their bites, and only a small quantity in one-third of those cases. Research in this area is hindered by the difficulty of identifying particular species.

Of the eight described species, P. nigriventer and P. fera most frequently receive mention in mass-media publications. P. nigriventer is the species responsible for most cases of venom intoxication in Brazil because it is commonly found in highly populated areas of south-eastern Brazil, such as the states of São Paulo, Minas Gerais, Rio de Janeiro and Espírito Santo. The species P. fera is native to the northern portion of South America in the Amazon of Brazil, Venezuela, Ecuador, Peru and the Guyanas.

The spider's wandering nature is another reason it is considered so dangerous. In densely populated areas, Phoneutria species usually search for cover and dark places to hide during daytime, leading it to hide within houses, clothes, cars, boots, boxes and log piles, thus generating accidents when people disturb it. Its other common name "banana spider" is attributed because it is occasionally found as a 'stowaway' within shipments of bananas. One such instance happened with a shipment of bananas arriving at Bridgwater, England, when a man was bitten by a P. fera, however due to quick medical care he survived, taking nearly a week to recover from the bite following treatment [7]

Despite their reputation as the world's deadliest spiders, there are multiple studies that call in to question their capacity for fatal human envenomation, though some of these are labelled with a level of uncertainty, as Phoneutrias easily can be confused with other species such as the Lycosides or other large labidognatha spiders. One study suggested that only 2.3 % of bites (mainly in children) were serious enough to require antivenom.[8]. However, other studies, as cited in the Wolfgang Bucheral studies, showed that the toxicity of Phoneutria venom was clearly more virulent than both Latrodectus and Atrax. Many experts believe that various spiders like Phoneutria can either deliver a "dry" bite or purposely conserve their venom as opposed to a more primitive spider like Atrax that usually delivers a full load. Nevertheless, there are well-attested instances of death. In one case, a single spider killed two children in São Sebastião. The spider was positively identified as a Phoneutria by Wolfgang Bucheral.[6].

The effect from a bite can be as simple as a couple of painful pinpricks or it can be fatal. In all cases, people bitten by a Phoneutria, or any Ctenid, should seek immediate emergency treatment.

[edit] Footnotes

  1. ^ Herzig V, John Ward R, Ferreira dos Santos W (2002). "Intersexual variations in the venom of the Brazilian 'armed' spider Phoneutria nigriventer (Keyserling, 1891)". Toxicon 40 (10): 1399–406. doi:10.1016/S0041-0101(02)00136-8. PMID 12368110. 
  2. ^ a b c d e f Martins & Bertani 2007
  3. ^ The world spider catalog, version 8.5. American Museum of Natural History. Accessed September 22, 2009.
  4. ^ Phoneutria nigriventer spider venom activates 5-HT4 receptors in rat-isolated vagus nerve
  5. ^ "Natural Viagra: Brazilian Spider Bite Causes Hours-Long Erection". FoxNews, May 1, 2007. Accessed May 6, 2007.
  6. ^ a b Venomous Animals and their Venoms, vol. III, ed. Wolfgang Bucheral and Eleanor Buckley
  7. ^ BBC, 2005
  8. ^ Bucaretchi et al., 2000

[edit] References

[edit] External links

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