Search

During collecting episodes in urban southern California, brown widow spiders, Latrodectus geometricus C. L. Koch, 1841, were observed to reside most often in specific locations such as acute angles within patio furniture or on the underside of railings. In this laboratory study, we tested several variables to determine which factors brown widow females may use for web site selection. All tests were conducted with corrugated cardboard refugia in enclosed dome-shaped insect cages. Brown widows were found to significantly prefer: 1) 30o angles compared to 60o or 90o angles, 2) cavities of 75 and 100 mm depth compared to 25 or 50 mm depth, 3) cavities lined with single-faced corrugated cardboard compared to smooth surfaces, and 4) refuges that had previously housed a brown widow compared to similar but previously unoccupied refugia. These data provide unusually detailed information about microhabitat selection by an urban pest, with possible implications for the pest control industry for eradication or for home owners to avoid envenomations.

Spider web construction is energetically costly, but it plays an important role in survivorship and reproduction. Studies have revealed facultative changes in spider web construction to adjust to available attachment sites. We used rectangular cardboard frames and two contrasting substrates to determine preferences in placement of gumfoot lines. This study demonstrated that mature females and first-instar nymphs of the brown widow spider, Latrodectus geometricus, display preferences for smooth substrates as sites to attach the gumfoot lines of their webs. First-instar nymphs also preferred to attach to the peaks when offered a wrinkled substrate. The preference of first-instar nymphs supports the hypothesis that substrate preferences for gumfoot line attachment may already be a selected behavior and not learned from previous experience.

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 range of the brown widow spider Latrodectus geometricus C. L. Koch includes much of Africa and South and Central America. This medically important spider has been recently introduced to Japan, Indonesia, Papua New Guinea, Australia, Hawaii, and California. After the identification of the brown widow spider in New Orleans, LA, and southern Mississippi, surveys in the southeastern United States were conducted from the fall of 2006 through February 2008. We found populations of brown widow spiders in Georgia, Texas, and multiple localities in southeastern Louisiana and Mississippi. In Mississippi, specimens were collected as far north as a county bordering Tennessee. In New Orleans, the brown widow spider has been commonly collected from various locations where human contact is likely.

The brown widow spider, Latrodectus geometricus C. L. KOCH, 1841, is recorded from Japan for the first time. Some females with egg sacs and numerous spiderlings were collected in the winter season in an urban park adjoining the container wharf at the port of Yokohama. According to the information received from colleagues by personal communication, spiders of this species were also found at the ports of Tokyo, Nagoya, Osaka and Okinawa, and some other dominant trade ports in Japan.