Brazilian Wandering Spiders
Wandering spiders are a family of spiders (Ctenidae) that includes the Brazilian wandering spiders, the most well-known and infamous of the family. The genus Phoneutria contains 9 species of which the Brazilian Wander Spider Phoneutria fera is the most famous. The genus name is from the Greek φονεύτρια, meaning "murderess". The common name, wandering spider, comes from the fact they do not spin webs to trap their prey but wander the forest floor hunting prey with their keen eyesight.
The genus Phoneutria includes some of the relatively few species of spiders that are of medical significance to humans, they are commonly found in close proximity to human habitation and fatalities are documented. There are documented cases of bites occurring in the UK when spiders have arrived as stowaways but there have been no fatalities. Symptoms may appear within 10 to 20 minutes after the bite, and death within two to six hours, where severe pain radiates to the rest of the limb, systemic effects include tachycardia, increased blood pressure, vertigo, fever, sweating, visual disturbances, nausea, vomiting, difficulty breathing and paralysis. Death is usually caused by respiratory arrest.
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 (revealing the conspicuous black/light-banded pattern on the leg underside), while the spider sways from side to side with hind legs in a cocked position.
Phoneutria are found in forests from Costa Rica southwards throughout South America east of the Andes including Colombia, Venezuela, the Guianas, Ecuador, Peru, Bolivia, Brazil, Paraguay, and into northern Argentina. Phoneutria has been introduced to Chile and Uruguay.
The spiders in the genus can grow to have a leg span of 13 to 18 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 (a dense brush of fine hairs) on the pedipalp tibiae and tarsi in both sexes. Phoneutria are easily confused with several other non-medically significant ctenids, especially Cupiennius.
These spiders acquired their other common name, "banana spider", because it is claimed that they are occasionally found in shipments of bananas, though the number of reports is exaggerated due to common misidentifications of unrelated spiders. A survey of spiders found in international shipments to the USA revealed that only 7 of 135 spiders were Phoneutria species. Spiders from genera such as tiger wandering spiders of the genus Cupiennius are commonly misidentified as being Phoneutria.
Whilst there are records of Phoneutria arriving in the UK as stowaways it is extremely rare. Most cases are in fact other species of banana spiders such as Cupiennius or Heteropoda that are innocuous to man.