Phoneutria, commonly known as Brazilian wandering spiders, armed spiders, or banana spiders,
are a genus of aggressive and venomous spiders of potential medical significance to humans.
They are mainly found in tropical South America, with one species in Central America. These
spiders are members of the Ctenidae family of wandering spiders.
The Brazilian wandering spiders appear in Guinness World Records from 2010 as the world's
most venomous spider. Guinness World Records states that although the Brazilian wandering
spider is the most toxic, an effective antivenom is available and few fatalities occur.
Description The genus Phoneutria contains eight scientifically
described species; the most notorious being P. fera and P. nigriventer. The spiders
in the genus can grow to have a leg span of 13 to 15 cm. Their body length ranges from
17 to 48 mm. While some other araneomorph spiders have a longer leg span, the largest
Phoneutria species have the longest body and the greatest body weight in this group. 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 easily
confused with several other non-medically significant ctenids, especially Cupiennius,
in which the recently described C. chiapanensis also has bright red hairs on the chelicerae.
Additionally, some Phoneutria species lack red hairs on the chelicerae, making it an
unreliable identification feature. The presence of a dark linear stripe or stripes on the
frontal palps and presence of a single thin black line running anterior-posterior along
the dorsal carapace may help identify Phoneutria. Other features are the strong ventral marking
on the underside of the legs with contrasting dark mid-segments and lighter joints, and
the pattern on the ventral of the abdomen with several rows of black dots, or an overall
reddish colour. The characteristic defensive posture with
frontal legs held high is an especially good indicator to confirm a specimen is Phoneutria,
especially alongside correct colour patterns. During the defensive display the body is lifted
up into an erect position, the first two pairs of legs are lifted high, while the spider
sways from side to side with hind legs in a cocked position.
Behavior 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.
Distribution Phoneutria are found in forests from Costa
Rica, and throughout South America east of the Andes into northern Argentina, including
Colombia, Venezuela, the Guianas, Ecuador, Peru, Bolivia, Brazil and Paraguay. Three
species are found in the Amazon region, one species is restricted to the Amazon, and one
ranges into Central America in Panama and Costa Rica. The remaining species are restricted
to Atlantic Forest of Argentina, Paraguay and Brazil, including forest fragments in
the Cerrado savanna. In Brazil, Phoneutria is only absent in the northeastern region
north of Salvador, Bahia. Phoneutria has been introduced to Chile and
Uruguay. Species
As of early 2012, this genus contains eight species:
Phoneutria bahiensis Simó & Brescovit, 2001 — Atlantic rainforest of Brazil.
Phoneutria boliviensis — Central, South America
Phoneutria eickstedtae Martins & Bertani, 2007 — Brazil
Phoneutria fera Perty, 1833 — Ecuador, Peru, Brazil, Surinam, Guyana.
Phoneutria keyserlingi — Atlantic rainforest of Brazil.
Phoneutria nigriventer — Brazil, northern Argentina; introduced to Uruguay.
Phoneutria pertyi — Atlantic rainforest of Brazil.
Phoneutria reidyi — Venezuela, Peru, Brazil, Guyana.
Toxicity and prey P. fera and P. nigriventer are widely considered
the most venomous species of spider. Its 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 a
bite 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 in humans. Erections resulting from the bite are uncomfortable,
can last for many hours and can lead to impotence. A component of the venom is being studied
for use in erectile dysfunction treatments. The amount of P. nigriventer venom necessary
to kill a 20 g mouse has been shown to be only 6 μg intravenously and 134 μg subcutaneously
as compared to 110 μg and 200 μg respectively for Latrodectus mactans. This ranks Phoneutria
venom among the most deadly spider venoms to mice. The Brazilian wandering spider's
prey also includes crickets, katydids, mantids, and other larger animals, including tree frogs
and lizards. Danger to humans
The genus Phoneutria includes some of the relatively few species of spiders known to
present a threat to humans. 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 are adapted to envenom very
small prey; they are not well-adapted to attacking large mammals such as humans. Some experts
believe that various spiders like Phoneutria can deliver a "dry" bite to purposely conserve
their venom, as opposed to a more primitive spider like Atrax that usually delivers a
full load. A study in March 2009 suggests that Phoneutria inject venom in approximately
one-third of their bites, and only a small quantity in one-third of those cases. Another
study similarly suggested that only 2.3 percent of bites were serious enough to require antivenom.
Other studies, as cited in the Wolfgang Bücherl studies, showed that the toxicity of Phoneutria
venom was clearly more potent than both Latrodectus and Atrax. Research in this area is hindered
by the difficulty of identifying particular species. 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 Bücherl.
Despite their reputation as the world's deadliest spiders, there are multiple studies that call
into question their capacity for fatal human envenomation, though some of these are labeled
with a level of uncertainty, as Phoneutria are often confused with other genera of ctenids,
lycosids or other large labidognatha spiders. 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 southeastern 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", comes from its tendency to hide in banana
bunches or plantations, and it is occasionally found as a stowaway within shipments of bananas.
These spiders can also appear in banana crates sent to grocery stores and bulk food centers
around the world. One such instance happened in 2005 with a shipment of bananas arriving
at Bridgwater, England, when a man was bitten by a P. fera. Due to quick medical care he
survived, taking nearly a week to recover from the bite following treatment.
Footnotes
External links