How to Manage Pests
Pests of Homes, Structures, People, and Pets
In the mid-1990s, Zoropsis spinimana, a large spider from the Mediterranean region, started showing up in homes around the San Francisco Bay area. It has since become well established around the southern, eastern, and northern portions of the Bay and has become a permanent member of the California spider population. Although the known distribution is not very extensive, this spider does inhabit a part of the state that is densely populated by humans and Zoropsis is routinely found in homes, causing concern among the people who encounter it. However, it is harmless to people. This Pest Note was prepared to provide information regarding this non-native resident.
The first California reports of Zoropsis spinimana were from the Sunnyvale area in Santa Clara County in 1992. Since then the spider has mostly spread north and east around the San Francisco Bay area with specimens found throughout Santa Clara, San Mateo, Alameda, Marin, and Santa Cruz Counties. Scientists at the California Academy of Sciences in San Francisco are tracking the spider’s spread. So far, Zoropsis spinimana seems to be found only in and around human dwellings. However, it is also possible that this spider is establishing itself in natural vegetation areas.
IDENTIFICATION AND BIOLOGY
Mature adults of Zoropsis spinimana are long-legged spiders about 1/2 to 5/8 inch in body length and with a leg span of 1 to 1 1/4 inches. Females have slightly larger bodies and shorter legs than males. For the most part, the Zoropsis spider is a typical brown spider of varying shades of brown mixed with little black markings over most of its body. In many respects, it resembles a wolf spider. One distinctive mark is a longitudinal, black mark with several outward flares on the central top surface of the abdomen, near the cephalothorax (the part of the spider to which the legs attach). Be aware that there are some species of wolf spiders that also have a black mark in this area; but most often, the wolf spider mark is diamond-shaped with only one flare at the center. Zoropsis spiders also differ from wolf spiders in the eye arrangement. Zoropsis eyes are restricted to the front edge of the cephalothorax; in wolf spiders the eyes are spread across the front third of the cephalothorax. Zoropsis spinimana can be distinguished from other common household spiders by these features: its abdomen is elongate (never globular) and it is never found in orb webs hanging between trees or on porches.
Zoropsis spinimana is a hunting spider (like wolf spiders), meaning it does not spin a web or use silk to subdue prey. Its silk is used primarily by the female to cover her egg sac. Like other spiders, its diet is primarily insects. Little information is available about the biology of this spider.
Most specimens that have been submitted for identification are mature males and females; this means that people are finding wandering spiders that are searching for mates or roaming in search of food or for other reasons. Mature specimens have been found from September to May and are commonly encountered throughout the winter. It is not known where the immature spiders spend the summers or if this spider requires more than one season to mature.
Despite the fact that this spider is large enough to be intimidating, Zoropsis spinimana is harmless. No spider in this genus is known to be medically important and there are no verified accounts of bites by this spider causing any significant medical problems.
Zoropsis spiders are harmless and control of them is unnecessary. The ones you encounter will be wandering adults so there is little you can do to prevent them from showing up in your home. If you feel you must do something, general spider preventive measures include reducing the clutter around your home, which eliminates hiding places that spiders find attractive. Adding weather-stripping around the base of doors will help keep spiders and insects from entering your home. It is unlikely that you will encounter more than one of these spiders at once; Zoropsis spiders do not appear in groups or invade in large numbers. Capturing and placing the spider outside will probably end your arachnid encounter and will not increase the probability of running into the spider later on. You can remove a spider from your home by placing a jar over it and slipping a piece of paper under the jar so that it seals off the opening of the jar when it is lifted up.
Griswold, C. E., and D. Ubick. 2001. Zoropsidae: a spider family newly introduced to the USA (Araneae, Entelegynae, Lycosoidea). J. Arachnology 29:111-113.
Vetter, R. S. 2007. Pest Notes: Spiders. Oakland: Univ. Calif. Agric. Nat. Res. Publ. 7442.
Pest Notes: Zoropsis spinimana
Authors: R. S. Vetter, Entomology, UC Riverside; D. Ubick, Entomology, California Academy of Sciences, San Francisco.
Produced by University of California Statewide IPM Program
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