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The mediterranean region covers portions of southern Europe, northern Africa and western Asia. Anyone who lives, has lived, or has vacationed in this region may know that it is home to numerous spider species, many of which are huge and scary looking. One fierce looking family of spiders that is native to the Mediterranean was found for the first time in the United States around 25 years ago. It is currently believed that this spider family is not associated with medically significant bites to humans. However, some reports from France suggest that these spiders can inflict bites that lead to tissue necrosis. These spiders are most heavily concentrated within the San Francisco area where they prefer to dwell within indoor locations.

The Zoropsidae spider family is relatively new to the continental United States. Researchers are not sure how or when exactly these non-native spiders arrived in the US, but it is believed that they have existed in the San Francisco Bay area since at least 1995. Surprisingly, not a single Zoropsidae spider species was ever found in North America before 1995. Even today, nearly 25 years later, experts do not know how this spider family was transported from the Mediterranean region to the west coast of the US, but some theories suggest that traveling individuals or shipments of plant materials brought the spiders into San Francisco. Whatever the case may be, researchers have long been baffled by this spider family’s ability to survive in conditions that are significantly different from the conditions that exist in its native region. In an effort to learn more about how these spiders survive in the US, researchers recruited help from residents. Since these spiders gravitate toward homes, researchers asked residents of San Francisco to email them a description and picture of any spider specimens that they believe could be from the non-native Zoropsidae family. After several years of field research in California, experts are not any closer to understanding how Zoropsidae spiders have adapted to a non-native California habitat.

Have you ever spotted a spider that you believed to be non-native?