Hide-and-seek with brown widow spiders

VIEW FULL MAP. Fig. 1: Distribution of established brown widow populations (yellow) and sporadic, smaller populations of brown widow (blue). Information originally compiled by Dr. John Wallace and Brian Daggs, Millersville University, Western Pennsylvania Conservancy. Learn more at StoryMaps.arcgis.com. SOURCE: ILLUSTRATION: MINIATURE/DIGITALVISION VECTORS/GETTY IMAGES

Latrodectus is a Greek word which, roughly translated, means “secret biter” or “biting in secret.” The first species of this genus was described in Italy by Rossi in 1790, as Aranea 13-guttata. It was later included in the Latrodectus clade by Walckenaer, 1805, who made the first correlation between bites of these spiders and the neurotoxic syndrome known as latrodectism. Symptoms include nausea, abdominal cramping, and burning and tenderness around the site of the bite.

Jumping in time to March 2021, the World Spider Catalog (Version 22.0. Natural History Museum Bern – 2021) lists 32 valid species of the genus Latrodectus worldwide. Fourteen of these species occur in the Americas, with five found in North America. Four of these North American species are native:

• Southern black widow (L. mactans)
• Northern black widow (L. variolus)
• Western black widow (L. hesperus)
• Red widow (L. bishopi)

The fifth species, the brown widow (L. geometricus), is invasive. It is generally believed to be introduced from Africa, where it is commonly called the button spider. It also epitomizes the characterization of being “secretive.”

Florida is ground zero

For decades after its mid-20th century introduction to the United States, the brown widow was mostly confined to the Florida peninsula. Today, it’s established in eight states, with nearly two dozen additional states reporting sporadic infestations (see Fig. 1).

Fig. 2: The cavity in the shovel handle. PHOTO: DR. HANIF GULMAHAMAD

It was first reported in California from specimens collected on a school campus in Torrance in 2003. (Editor’s Note: The author wrote about this finding in Pest Management Professional’s June 2003 issue, available online at MyPMP.net/wp-content/uploads/2023/09/PMP-June-2003.pdf; the article starts on the fourth page.) But while this is the first official record of its presence in southern California, subsequent inspections by this author of properties surrounding the school suggest this spider was present in the area for quite some time before it was discovered. The fact that it was not found earlier was because, quite simply, no one was looking for it.

Uncovering harborage sites

Twenty years on, the brown widow is now ubiquitous in southern California, but is seldom observed because of its reclusive habit. This spider builds its small, nondescript web in sheltered and secluded places. Female spiders ensconce themselves in cozy hideouts. These spiders are largely nocturnal and rarely venture out in the open during the day, so casual inspections are not likely to reveal their presence on a property.

In highly sensitive situations, such as schools and daycare centers, nocturnal inspections are recommended.

Fig. 3: The shovel cavity with egg sacs. PHOTO: DR. HANIF GULMAHAMAD

One good way to confirm the presence of a brown widow spider is by locating its spherical egg sacs. These cream-colored, spiky structures have pointed projections all over their surfaces, sometimes referred to as spicules. To find these eggs sacs, you must know where to look. Some of these spider harborages are not easy to locate.

The purpose of this article is to point out three almost implausible microhabitats where the brown widow spider was found recently around a single-family residence in Montclair, Calif.:

1. Shovel handle: A shovel that was leaned up against the outer wall of a home was used by the homeowners to scoop dog waste, so it was moved sporadically. Figs. 2 and 3 show the shovel’s handle cavity, and the presence of brown widow spider cases. The cavity is about 3.5 inches in length at the bottom of the wooden handle and the metal shovel itself. Fig. 4 shows four egg cases that were teased out of the shovel handle cavity.

Fig. 4: Four egg cases were teased out of the shovel handle cavity. PHOTO: DR. HANIF GULMAHAMAD

2. Garden hose hanger: This wall-mounted holder (see Fig. 5) is attached to the homeowners’ garage. The homeowners had hired a professional crew to paint their house’s exterior, and upon removing the holder, three brown widow spider egg sacs were revealed on its underside. The section of the hose holder that was attached to the house had a small cavity behind it, which was where the female spider was sheltering (see Fig. 6). The number of egg sacs present indicate this spider was living there for some time. A single female brown widow spider can produce nine egg sacs in a single summer. This number is speculative, however, because many factors affect egg sac production — such as prolonged favorable temperatures and an abundance of prey.

Fig. 5: The water hose hanger, as it was previously mounted before removal. PHOTO: DR. HANIF GULMAHAMAD

3. Patio side table: When the small wooden table (see Fig. 7) was turned upside down, a brown widow spider egg sac was found in a corner (see Fig. 8).

The presence of this spider species in the microhabitats described above illustrate the fact that this spider can be very easily transported by everyday activities such as using a shovel, unspooling a garden hose or moving a patio table across the yard.

The bottom line? Inspect thoroughly to maximize productivity and efficiency.

Fig. 6: Note the harborage cavity on the underside of the hose hanger. PHOTO: DR. HANIF GULMAHAMAD

Fig. 7: The backyard patio table is short and nondescript. PHOTO: DR. HANIF GULMAHAMAD

Fig. 8: An underside, secluded corner of the table served as harborage for an egg sac. PHOTO: DR. HANIF GULMAHAMAD