Patterns of the introduction, spread, and impact of the brown widow spider, Latrodectus geometricus (Araneae: Theridiidae), in the Americas

Introductions of non-native species to novel environments happen often, but a species must overcome multiple biotic and abiotic filters to establish and eventually spread. Focusing on patterns of introductions can provide insights as to underlying mechanisms that facilitate establishment, and in turn, their potential effects on native communities. The brown widow spider, Latrodectus geometricus C. L. Koch, 1841, is likely native to Africa, but now has a cosmopolitan distribution due to introductions via international trade. We reviewed the patterns of brown widow introductions in the Americas to determine if there are any large-scale inferences regarding their patterns, and potential impacts, of their introduction. A total of 5,004 records from 30 countries were synthesized and demonstrate their spread to higher latitudes across time with the majority of those records (n = 4,923; 98%) occurring in the past two decades. Brown widows are now documented in 30 of the 35 countries in North, Central, and South America, with one-third of those introductions detected in the last 30 years. Citizen-science databases (e.g., iNaturalist) have been instrumental in documenting the expansion of the brown widow, as more than 90% of the records synthesized came from these sources. Brown widows have proven to be successful invaders worldwide, and this review synthesizes expansion reports of their invasion in the Americas in hopes of spurring additional research in locations where they have become established.