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Sac spiders from the genus Chicaricanthium are among the most commonly sighted, and dangerous, spider species in the United States. The two most commonly spotted sac spider species in the US, Cheiracanthium inclusum and Cheiracanthium mildei, do not inflict bites that are as medically significant as the bites inflicted by brown recluse and black widow spiders, but sac spider bites cause tremendous localized pain that can last for several hours or up to 48 hours. Many bite victims develop painful blisters at the site of the bite wound, and a smaller proportion of bite victims develop systemic symptoms, such as fever, malaise, muscle cramps, and nausea. There is ongoing debate about whether or not the C. mildei species has inflicted bites that develop localized tissue necrosis. A study of C. mildei bites in Italy suggests that necrotic bite wounds have been inflicted in rare cases by this species.

Several other studies have shown that this species often inflicts necrotic bite wounds on guinea pigs and other animals, but evidence showing this reaction in humans remains sparse.

The Cheiracanthium inclusum and Cheiracanthium mildei sac spider species, are more commonly referred to as “agrarian sac spiders,” and “longlegged sac spiders,” respectively. The agrarian sac spider is indigenous to the US, and they are less prone to bite than the non-native longlegged sac spider. The longlegged sac spider was introduced into Massachusetts from Europe where the species remains far more abundant than the agrarian sac spider. Although the longlegged sac spider has increased its habitat range in the US, these spiders have a long history of inflicting dangerous and exceedingly painful bites to humans in urban Boston. The longlegged sac spider has also grown accustomed to living within human habitats in order to find more prey, leading researchers to declare this spider a synanthropic species. As a synanthropic species, the longlegged sac spider can establish itself permanently within homes. Unsurprisingly, a report of 111 longlegged sac spider sightings had all but three occur indoors. Not only is this species dangerous, but they are also aggressive, as they are not shy about crawling on human skin where they often bite without provocation.

Have you ever sustained a yellow sac spider bite?