When the subject of dangerous spiders comes up, the average person usually thinks about the black widow spider. Their shiny black body with a prominent red hourglass marking on the underside of the abdomen is an image that readily comes to mind.
In Florida, however, there are three other venomous widow spiders (Southern black widow, northern black widow, and, the red widow) in addition to the brown widow. The most commonly encountered species of the group that people are finding around their homes and work place in Sarasota County is the brown widow spider, Latrodectus geometricus. In the mid to late nineties there seems to have been an outbreak of brown widow spiders. Since this article was first written in 2000, this spider has spread throughout Florida and people have reported sightings of it from Southern California, Colorado, Texas, Arkansas, Mississippi, Alabama, Georgia, and South Carolina. Complaints about its occurrence in cars and RVs indicate this spider will make it home in these sites. Cars, trucks, and RVs have probably helped to distribute this spider far and wide. It rapid expansion in Florida in the late 90s may have been the result of the milder winters. However, the most important factor in its expansion has probably been transportation by vehicles. The Extension Office continues to receive complaints asking how to rid them from in and under cars
Because they vary from light tan to dark brown or almost black, with variable markings of black, white, yellow, orange, or brown on the back of their abdomens, brown widows are not as easy to recognize. The underside of the abdomen, if you can see it, contains the characteristic hourglass marking. Unlike the black widow, the hourglass is orange to yellow orange in color.
With the brown widow, however, there is another way to detect its presence. Its egg sac is very different from those of the other widow spiders. Instead of the smooth white to tan surface, the outside of the egg sac is covered with pointed projections giving it the appearance of a globe with many pointed protuberances on its surface. It has also been described as tufted or fluffy looking.
Although the bite of a widow spider is much feared, the widow spiders are generally non-aggressive and will retreat when disturbed. Bites usually occur when a spider becomes accidentally pressed against the skin of a person when putting on clothes or sticking their hands in recessed areas or dark corners. According to Dr. G.B. Edwards, an arachnologist with the Florida State Collection of Arthropods in Gainesville, the brown widow venom is twice as potent as black widow venom. However, they do not inject as much venom as a black widow, are very timid, and do not defend their web. The brown widow is also slightly smaller than the black widow.
The brown widow builds its web in secluded, protected sites around our homes, often very near our presence. It has a fondness for buildings but will construct its web in all kinds of man-made structures, and even vegetation. Some typical sites include inside old tires, empty containers such as buckets and nursery pots, mail boxes, entry way corners, under eaves, stacked equipment, cluttered storage closets and garages, behind hurricane shutters, recessed hand grips of plastic garbage cans, undercarriages of motor homes, underneath outside chairs, branches of shrubs. The following photographs show some sites where brown widows have constructed their webs.