Most Wanted: American Yellow Sac Spider


January 16, 2014

Arachnology is the study of spiders. As arachnologists, pest management professionals (PMPs) investigate envenomation. Spiders use venom consisting of cytotoxic, proteolytic and hemolytic components. Victims might suffer localized hemolysis (the destruction of blood cells), leading to a mild stinging sensation.

For this modus operandi, the usual suspect is the American yellow sac spider (AYSS), Cheiracanthium inclusum. With two distinct body segments (the cephalothorax and abdomen), AYSS females are 5 to 9mm, and males are 4 to 8mm. The front pair of pasting podites exceeds the length of the successive three pairs (2.5 cm legspan). Females are more robust than males. The AYSS is pale yellow-beige with dark-brown colorations on its palps (structures behind the chelicerae on the cephalothorax), chelicerae (jaws) and distal tarsi (feet). An orange-brown stripe runs along the top center.

The AYSS possesses eight eyes distributed in two, parallel horizontal rows. Visual perception is less profound because of afferent sensitivity resulting from its palps. When not constructing webs to capture prey, the nocturnal predator feeds on arthropods and other spiders. Prey can be detected by mechanical vibrations on a substrate.

During the day, the AYSS takes refuge within a small silk sack, which is comparable to those used for reproduction. Easily constructed in about 10 minutes, the sac can be closed wholly, exposed on one side or exposed on both sides. After excreting a long silk strand, the AYSS absconds via balloon-wind dispersal, adhering to structures and forming a scaffold.

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