The Brazilian wandering spider or (Phoneutria spp.), armed spider ("aranhas armadeira", as they are known in Portuguese) or banana spider (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.
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 10-13 cm (4-5 in). Their body length ranges from 17 to 48 mm (0.7-1.9 in). 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. 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.
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.
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.
Phoneutria has been introduced to Chile and Uruguay.
Phoneutria has a highly venomous bite. This genus includes some of the relatively few species of spiders known to present a threat to human beings.
These spiders are notorious both because of their toxic venom, and because they are not reluctant to attack people who appear threatening. 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 commonly is 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.
Recent[when?] studies suggest that these spiders only inject venom in approximately one-third of their bites and may only inject a small amount in another third. However, research in this area is hindered by the difficulty of identifying particular species.
Bites from these spiders may result in only a couple of painful pinpricks, or may involve full-blown envenomation; but in all cases, people bitten by a Phoneutria, or any Ctenid, should seek immediate emergency treatment, as the venom can be life threatening. P. fera and P. nigriventer are the two most commonly implicated as the most virulent of the Phoneutria spiders.
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.
Aside from causing intense pain, the venom of the spider can also cause priapism - uncomfortable erections that can last for many hours and lead to impotence. A component of the venom (Tx2-6) may eventually be used in erectile dysfunction treatments.
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 - the "banana spider" - as attributed because it is occasionally found as a 'stowaway' within shipments of bananas.
Despite their reputation as the world's deadliest spiders, there are multiple studies that dispute their capacity for fatal human envenomation. One study suggested that only 2.3% of bites (mainly in children) were serious enough to require antivenom. However, other sources suggest they are the most dangerous or toxic spiders in the world based upon toxicology studies, with one study demonstrating that the amount of Phoneutria nigriventer venom necessary to kill a 20g mouse is only .006 mg (intravenously) and .0134 subcutaneously as compared to 0.110 and 0.2 respectively for Latrodectus mactans (Black Widow). The same study reports the death of two children killed by the same spider in São Sebastião identified as a Phoneutria, and identified by Bucheral. This demonstrates the fact that identification is key in the process of accurately associating a bite with the correct, offending species. Both P. nigriventer and P. fera are extremely dangerous. Pharmacological studies strongly suggest the danger of Phoneutria envenomation and ranks various species of the Phoneutria genus arguably as one of the world's most dangerous spiders.
