The Brazilian wandering spider, belonging to the genus Phoneutria, is known for its potent venom. This often leads to the misconception that they are aggressive. While their venom is medically significant, their behavior is often misunderstood. This article clarifies their nature and provides practical information on encounters and bites.
Understanding Their Behavior
Brazilian wandering spiders are named for their habit of roaming the jungle floor at night, rather than constructing webs to capture prey. They are primarily nocturnal ambush predators, hunting insects, small amphibians, reptiles, and other spiders. They seek refuge in dark, undisturbed places during the day, such as under logs, leaf litter, or inside human dwellings like clothes, shoes, or banana shipments.
Bites often occur when the spider feels threatened, trapped, or is disturbed. When confronted, these spiders adopt a distinct defensive posture, raising their front legs high to display their fangs and contrasting undersides. This display is a warning signal, not an immediate intent to attack. Bites occur if this warning is ignored or the spider is provoked.
Recognizing the Spider
Brazilian wandering spiders have several key physical characteristics. They are large, hairy spiders, with a leg span up to 7 inches (18 cm) and a body length of 1.7 to 4.8 cm. They are commonly brown or gray, often with dark leg bands for camouflage.
Their defensive stance is distinctive: they raise their first two leg pairs, revealing a patterned underside with black and light bands. Some species may also have red hairs on their chelicerae, but this is not a reliable identification marker. While these descriptions offer general guidance, definitive identification is challenging for non-experts and should not be the sole basis for safety decisions.
Encountering the Spider
If you encounter a suspected Brazilian wandering spider, maintain a safe distance. Avoid provoking the spider, as most bites occur when it feels cornered or disturbed. Do not attempt to handle or capture the spider directly.
If the spider is in a home, calmly back away and secure the immediate vicinity to prevent it from moving into living spaces. Contact local pest control or emergency responders for safe removal. Shaking out clothing or shoes before use, especially in common regions, can prevent accidental encounters.
After a Bite
If a bite occurs, seek immediate medical attention, especially for children and the elderly. Initial symptoms include severe burning pain, localized swelling, redness, and sweating at the bite site. Widespread symptoms can develop within about 30 minutes.
Systemic effects may include blood pressure fluctuations, heart rate changes, nausea, abdominal cramping, and blurred vision. In males, priapism (a prolonged, painful erection) can occur. Clean the bite area with soap and water and apply a cold compress for immediate first aid, but these do not replace professional medical evaluation. Antivenom is available and crucial for managing severe envenomations. While fatalities are uncommon, prompt medical intervention reduces the risk of serious complications.