Field Guide to Venomous and Medically Important Invertebrates ...

Yellow Sac spiders
More than 200 species of yellow sac spiders in the genus Cheiracanthium are distributed
worldwide. Some of the known dangerous species of Cheiracanthium are shown in Appendix 1.
These spiders are relatively small (0.4 inch or 10 mm, body length), and yellowish in color. Sac
spiders construct sack-like, silken tubes in foliage or under bark or stones in which they hide.
Although fairly reclusive in nature, sac spiders will occasionally enter houses and other
structures. Yellow sac spiders are aggressive and will bite defensively. The clinical significance
of these spiders is not well known, but they have been shown capable of causing a painful bite
with associated necrosis and occasionally systemic effects. However, several species of
Cheiracanthum have been implicated in human envenomations, and they reportedly are
responsible for upwards of 90% of all dangerous spider bites in South Africa.
The number of species of yellow sac spiders which can inflict dangerous bites is not known, but
because some species are considered dangerous, all sac spiders should be considered a potential
threat. Many reported ―brown recluse‖ bites outside the known range of Loxosceles reclusa in
the United States may be due to envenomation by yellow sac spiders or perhaps other spiders. In
the United States C. inclusum is native while C. mildei is introduced. Cheiracanthium mildei
was first identified as a cause of necrotic arachnidism in 1970, when it was linked with skin
lesions in the Boston, Massachusetts area where it is the most common spider found in houses.
This species also is common in houses in New York City, and may well be the cause of "brown
recluse‖ bites rumors mistakenly reported from that area. In the late 1970's and early 1980's C.
mildei produced a significant number of bites in the Provo, Utah area. Similarly, C. inclusum is
reportedly responsible for bites in Georgia and southwestern Canada. Bites by C. inclusum are