The yellow sac spider, also known as the black-footed yellow sac spider or the American yellow sac spider, is a species of spider that is native to North, Central and South America. The venomous spiders are common in the United States, Mexico, and parts of South America, although some species of yellow sac spiders can also be found in Africa and the island of Réunion, which is an overseas region and department of France. The yellow sac spider is nocturnal, spending time in silk nests during the day, and hunting and mating at night. They can be found crawling on walls and vertical surfaces, and also construct silk sacs or tubes in isolated areas such as timber yards, wall junctions, or in ceilings. Some species of yellow sac spider are attracted to the smell of gasoline and can be found living under vehicles. In fact, between 2010 and 2012, auto manufacturer Mazda recalled one of its vehicle models after repeated complaints of leaks and loss of power. The manufacturer discovered that yellow sac spiders were weaving dense webs in the vehicle's canister vents, resulting in blockages and buildups of pressure.
The yellow sac spider has powerful fangs that can easily penetrate human skin. Most human bites occur when performing gardening or outdoor activities. The spider’s venom affects cells and nerve tissue, and in extreme cases the spinal cord and brain, although no fatal incidents have ever been recorded. Many people are unable to differentiate between the yellow sac spider and the brown recluse spider, and most bites attributed to the brown recluse spider are actually inflicted by the yellow sac spider. Victims are advised to seek immediate medical treatment due to the necrotic nature of the bite.
Instead of making webs to catch prey, the yellow sac spider is an active hunter that emerges at night from its silk sac in search of prey. Yellow sac spiders feed on arthropods, including their eggs, and larger spiders. While outdoors, they also search foliage for small insects. Due to their hunting habits, yellow sac spiders occasionally enter human homes, especially during autumn, when the food supply dwindles.