Invertebrates
Brazilian Wandering Spider
Phoneutria nigriventer · also called brazilian wandering spider, armed spider, banana spider
The Brazilian wandering spider is a big, fast, ill-tempered hunting spider from the American tropics, famous for a venom that ranks among the most potent of any spider and for a habit of turning up in places people would rather it did not — woodpiles, shoes, houses, and, occasionally, boxes of bananas on another continent. It spins no web. Instead it walks the forest floor every night looking for something to catch.
Overview
Brazilian wandering spiders belong to the genus Phoneutria, meaning “murderess” in Greek. They range across Central and South America, but the species that matter medically are concentrated in southern and southeastern Brazil and nearby countries. The body is 3.5–5 cm long and the leg span can reach 13–18 cm, all of it clothed in fine grey-brown hair, with distinctive reddish jaws.
A hunter without a web
These are active wandering predators. By day they shelter in dark, humid crevices — under logs and leaf litter, in bromeliads and banana plants, inside sheds and homes. By night they roam across the ground and low vegetation, using vibration, touch, and low-light vision to find insects, other spiders, and small frogs and lizards, which they run down and bite rather than trap.
The threat display
Cornered, a Brazilian wandering spider does not flee quietly. It rears onto its back legs, lifts and spreads its front legs high to show their pale undersides and the red jaws beneath, and sways from side to side. It is a genuine warning: a spider in this posture will strike if pressed, and it can move very quickly.
The venom
The venom is a cocktail of small peptide toxins that interfere with nerve and muscle signalling. A serious bite can bring intense pain, heavy sweating, a racing or irregular heartbeat, excess saliva, and, in severe cases in young children, difficulty breathing. One toxin causes a prolonged, painful erection, a symptom that has led researchers to study a modified form of the molecule as a possible erectile-dysfunction drug.
Danger in perspective
The reputation outruns the reality. Only a few Phoneutria species are dangerous, full-dose bites are uncommon, and antivenom is produced and stocked throughout the spiders’ range. Fatalities are now very rare and fall almost entirely on untreated small children. The spider is genuinely well armed — but with prompt hospital care, people bitten by it almost always recover.
Brazilian Wandering Spider: common questions
Is the Brazilian wandering spider the most venomous spider in the world?
It is often given that title, and by some measures of venom toxicity in laboratory tests it ranks at or near the top among spiders. In practice the picture is more complicated. Only a few of the roughly nine Phoneutria species are dangerous to people, bites that inject a significant dose are uncommon, and effective antivenom is produced and stocked across the spiders' range in Brazil. Deaths are now very rare and occur mainly in small children who receive a full bite and are not treated. So while the venom itself is extremely potent, the spider is not the reliable killer that its reputation suggests.
Why is it called the banana spider?
Because it sometimes turns up far from home in shipments of bananas and other tropical produce. The spiders hide by day in tight, dark, humid spaces, and a bunch of bananas or a packing crate is exactly the kind of refuge they seek out. Occasionally one is carried along with the fruit to a supermarket or a home in Europe or North America, which generates alarming news stories. Such stowaways are almost always a single spider, are usually found dead or sluggish from the cold, and the species most often intercepted this way is frequently a harmless relative rather than a dangerous Phoneutria.
How does the Brazilian wandering spider hunt without a web?
It relies on speed, good low-light vision, and an acute sense of vibration and touch through hairs on its legs. At night it leaves its daytime refuge and patrols the ground and low plants, detecting prey by the movements they make. When it senses an insect, another spider, or a small frog within reach, it rushes forward, seizes the prey with its front legs, and delivers a venomous bite that quickly subdues it. Because it does not invest in silk to build a snare, it must cover ground actively every night, which is why it wanders so widely and why it so often ends up somewhere a person does not expect.
What should you do if bitten by a Brazilian wandering spider?
Treat it as a medical emergency and get to a hospital quickly, taking a photograph of the spider if that can be done safely, because most bites turn out to be from harmless species and identification changes the treatment. Keep the bitten limb still and roughly level with the heart, and do not cut the wound, apply a tight tourniquet, or try to suck out venom. In the spiders' range, hospitals stock antivenom and give it when symptoms are severe, alongside pain relief and monitoring of heart and breathing. Most people who reach care recover fully.