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The brown widow spider, Latrodectus geometricus C. L. Koch 1841, is non-native to North America and has experienced an explosive range expansion in the first decade of the 21st century. Previously restricted to peninsular Florida, it is now well established in the southeastern United States and southern California. In southern California, brown widow spiders have become ubiquitous around urban homes and are well known to the general public because of their high numbers and distinctive spiked egg sacs. Several insects attack egg sacs of the native western black widow, L. hesperus Chamberlin & Ivie 1935, as either parasitoids or egg predators. We investigated whether and to what degree these insects would attack brown widow egg sacs. We dissected 3,739 brown widow egg sacs finding evidence of the chloropid fly, Pseudogaurax signatus (Loew 1876) in 2.0% and wasp parasitoids in 0.4% of the sacs. For comparison, we also dissected 263 western black widow egg sacs with P. signatus showing a higher level...

The brown widow spider, Latrodectus geometricus C. L. Koch, 1841, is a non-native arachnid that became established in peninsular Florida in the 1930s (Pearson 1936). In the first decade of the 21 century, it rapidly spread through the southeastern United States and southern California (Brown et al. 2008; Vincent et al. 2008; Vetter et al. 2012a) and has become a ubiquitous urban pest species in the Los Angeles Basin and San Diego area (Vetter et al. 2012b). One possible reason for its success lies in its fecundity, as it can produce an egg sac every four days during its earliest ovipositions and averages 22 egg sacs in a lifetime (Bouillon and Lekie 1961). We were interested in documenting the seasonal field egg production of brown widows from June to October to determine whether there is a specific peak and subsequent dropoff in productivity or whether it is fairly consistent throughout the summer season. This provided basic biology information that benefitted research involving insecticide bioassays on brown widow egg sacs (Vetter et al, in prep); knowing the phenology of seasonal clutch size helped determine whether lab-produced egg sacs would be temporally comparable with natural oviposition and, hence, whether pesticides tested on egg sacs would have real world relevance. To determine monthly egg clutch size, brown widow egg sacs were collected during the day from several cities in Orange and Riverside counties, California from June through October 2012. Collections were restricted to urban sites such as around homes, in parks, under playground equipment, etc. as documented favored habitats for this spider (Vetter et al. 2012b). We attempted to collect egg sacs primarily from sites that were occupied by female brown widows as this presumedly increased the chances of collecting sacs with freshly laid eggs. The study was terminated at the end of October because temperatures cool considerably in November in southern California. We did not collect egg sacs for the first seven days of any month in order to more accurately assign sacs with eggs to the correct month of oviposition. At 29uC, brown widow eggs hatch in 9 days. Considering that daily high temperatures in many of our collection locales are typically 35 to 40uC, we felt that this was an acceptable estimate to separate clutch size into monthly cohorts. We also received some sacs in the mail from citizen scientists who participated in previous brown widow studies (Vetter et al. 2012a,b); again, no data from sacs collected and received during the first week of the month were used.

Metaltella simoni (Keyserling, 1877) (Amphinectidae) is a South American spider that has become established in urban southern California. Earlier publications remarked on its scattered presence, however, it has since become common enough that it can be easily found in many cities with minimal searching.

The brown widow spider, Latrodectus geometricus C. L. Koch, has become newly established in southern California during the first decade of the 21st century. Brown widows and egg sacs were collected within the urban Los Angeles Basin using timed searches. We also collected and compared the abundance and distribution of the native western black widow spider, Latrodectus hesperus Chamberlin & Ivie, to brown widows. Brown widows were very common around urban structures especially outside homes, in parks, under playground equipment, in plant nurseries and landscaping areas, greatly outnumbering native western black widows, and were very rare or nonexistent in garages, agricultural crops, and natural areas. Western black widows predominated in xeric habitats and were less prevalent around homes. Neither species was found in the living space of homes. In southern California, envenomation risk exists because brown widows are now common in urban areas and the spiders hide where people place their fingers and exert pressure to move objects (e.g., under the curled lip of potted plants, in the recessed handle of plastic trash bins). Nonetheless, brown widow spider bites are less toxic than those of native western black widow spiders and, hence, if they are displacing black widows, overall widow envenomation risk may actually be lower than before brown widow establishment.