The Prevalence of Brown Widow and Black Widow Spiders (Araneae: Theridiidae) in Urban Southern California

Abstract

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.

Habitat, redescription and distribution of Latrodectus geometricus in Uruguay (Araneae: Theridiidae)

“…All these considerations support the assumption that L. geometricus is in a great expansion of its distributional range, as was reported for others parts of the world (Garb et al 2004). Recently, Vetter et al (2012) reported the frequent presence of the brown widow spider in urban areas of southern California, USA, and the prevalence of this species in cities, around buildings, in greater numbers than the native black widow, Latrodectus hesperus Chamberlain & Ivie 1935, the latter being more common in natural and agricultural areas. Similarly, in Uruguay L. geometricus prevails in urban habitats in contrast to the native L. mirabilis which lives in grasslands under stones or in agricultural crops.…”

“…The urban habitats occupied by Latrodectus geometricus in Uruguay and the association of this species with synanthropic habitats are similar to that indicated to from other cities as windows frames and wall crevices in New Orleans and California in U.S.A. (Brown et al 2008, Vetter et al 2012 or under park benches in Yokohama, Japan (Ono 1995). At the same time the web architecture is similar to that described by Eberhard et al (2008).…”

“…Similarly, in Uruguay L. geometricus prevails in urban habitats in contrast to the native L. mirabilis which lives in grasslands under stones or in agricultural crops. Although L. geometricus shows non-aggressive behavior and human envenomation by brown widow spiders are less severe than those caused by other Latrodectus species (Brown et al 2008, Vetter & Isbister 2008, Vetter et al 2012, its presence in urban habitats and its potential dispersal to other parts of Uruguay represents a new agent of health and pest control interest in this country. The high dependence of L. geometricus to live associated with humans shows the potential condition of this species as a good bioindicator to detect environmental disturbance in natural habitats.…”

“…Although envenomations by L. geometricus are considered less severe than those of other species of the genus (Vetter & Isbister 2008), the cases reported vary from local to systemic damages (Cardoso et al 2003, Kiriakos et al 2008). This species has an affinity for human structures and residential buildings (Bayram et al 2008, Brazil et al 2009, Vetter et al 2012 where it constructs a web of irregular shape. This web is characterized by the presence of a retreat located at the top with a central disc and gumfoot lines with fluff mass and balls of glue (Eberhard et al 2008) The round egg sacs show very characteristic protuberances of silk spikes (Vincent et al 2008).…”

Potential for CFC in Black Widows (Genus Latrodectus): Mechanisms and Social Context

“…Widows are well known in popular culture because of their neurotoxic venom (Jelinek 1997;Ushkaryov et al 2004), the tendency of several species to thrive in anthropogenically disturbed habitats (Trubl et al 2012;Vetter et al 2012), and because of their lurid reputation for females that kill and consume courting males (D'Amour et al 1936). In reality, there is a wide range of mating systems in this genus (e.g., Breene and Sweet 1985;Forster 1992;Andrade 1996;Knoflach and van Harten 2002;Segev et al 2003;Segoli et al 2006), ranging from polygyny and polyandry to the most extreme examples of male monogyny enforced by polyandrous female cannibals (observed in two species to date : Forster 1992;Segoli et al 2008a).…”