The phylum Arthropoda is composed of insects, arachnids, centipedes, crustaceans, and other invertebrate organisms. Arthropods rely on resources within their native habitats in order to survive, but a small minority of arthropod species are capable of thriving in a variety of ecological conditions well outside of their native range. Ants, beetles, and cockroaches are just a few types of arthropods that are regularly and inadvertently transported to exotic locations around the world within infested shipping cargo, airplane luggage, and international mail.

Non-native arthropod species usually cause ecological, medical, and/or economic harm in areas outside of their native range. These harmful non-native species are known as “invasive pests,” and they include red imported fire ants, Argentine ants, and Formosan subterranean termites in the US. Since southern California is home to the two busiest shipping ports in the country, it’s not surprising that the state has become home to the highest number of invasive arthropod species in the US, with the possible exception of Florida.

Between the years of 1700 and 2015, at least 1,686 non-native arthropod species established a permanent habitat in California, and many of them are invasive pests that infest homes in Ventura County. Of these non-native arthropod species, 84.4% are insects, 7.4% are mites, and 3.2% are spiders. Some of these non-native species are now among the most commonly managed indoor pests in California, and they include silverfish (Lepisma saccharina), European earwigs (Forficula auricularia), pillbugs (Armadillidium vulgare), American cockroaches (Periplaneta americana), German cockroaches (Blattella germanica), Argentine ants (Linepithema humile), and even house flies (Musca domestica).

Three recently established non-native spider species in California have already been found infesting homes in the region, two of which are considered a potentially dangerous species in their native regions. These species are known as brown widow spiders (Latrodectus geometricus), noble false widow spiders (Steatoda nobilis), and antmimic spiders (Falconina gracilis). Brown widows were first discovered in Los Angeles, but they have since migrated into neighboring Ventura County. While individuals have been hospitalized as a result of brown widow envenomation, such reactions are very rare. Although closely related to notorious black widow spiders, noble false widow bites result in medically significant reactions less frequently than bites inflicted by brown widows. These spiders were first discovered in Ventura County where they are now common house spiders. The antmimic spider is rarely found in Ventura County, and the bites they inflict, while painful, are not known to cause serious medical conditions.

Have you ever found a large number of spiders hiding within a dark space within your home?

Leave a Reply