The brown widow spider, Latrodectus geometricus, is a member of the widow family, which also includes the black widow. Although its exact origins are unclear (some evidence points to Africa), it was first formally described from South America and is now found worldwide in tropical and subtropical regions. This invasive species has rapidly expanded its range across North America, particularly in the southern United States, since the early 2000s, thriving in environments near human habitation.
Identifying the Brown Widow
The female brown widow typically reaches a body length of 12 to 16 millimeters, excluding the legs. Its coloration is variable, ranging from pale tan or cream to light brown, or occasionally dark gray or nearly black. This mottled appearance, often with dark markings and white stripes on the abdomen, contrasts sharply with the solid, glossy black of the black widow. A distinct feature is the dark banding present at the joints of the legs.
Like other widow species, the most recognizable mark is the hourglass shape located on the underside of the abdomen. In the brown widow, this marking is typically orange or yellowish-red, rather than the vivid red seen on a black widow.
Distinguishing Features: Webs and Egg Sacs
Brown widow webs are irregular, messy, or tangled structures made of sticky, strong silken fibers. They often include a silken retreat where the spider hides. Finding the spider’s egg sac is often the most reliable method for confirming the species.
The egg sac is small, spherical, and pale white, tan, or yellowish. Unlike the smooth, pear-shaped sacs of the black widow, the brown widow’s sac is covered in numerous tiny, stiff, spiky protrusions. These projections give the egg sac a tufted or fluffy appearance, sometimes described as resembling a naval mine or a sandspur.
Understanding the Bite and Venom
The brown widow’s venom is a potent neurotoxin, like that of all Latrodectus species, containing the active component alpha-latrotoxin. This toxin disrupts nerve signaling at neuromuscular junctions. Despite the venom’s potency, brown widow bites are generally considered less medically significant than black widow bites. This reduced severity is primarily because the brown widow typically injects a smaller amount of venom defensively.
Symptoms are often localized to the bite site, including immediate pain, redness, and a small puncture mark. Systemic symptoms like muscle cramps, stiffness, or nausea are usually mild and less frequent than those caused by the black widow. First aid involves cleaning the area with soap and water and applying a cold compress to manage localized swelling and pain.
Most bites resolve within a few hours to a couple of days. Medical attention should be sought if symptoms worsen, spread, or if severe systemic reactions like intense muscle cramping or difficulty breathing occur. Only the mature female is capable of biting, usually doing so defensively when accidentally pressed against the skin.
Common Habitats and Geographic Spread
The brown widow spider has a preference for tropical and subtropical climates and is now widely distributed across the globe, including established populations in Australia, Japan, and the southern United States. Its spread is closely linked to human activity, as it is easily transported through global trade and on vehicles. Within its range, the spider is an urban exploiter that builds webs in secluded, protected sites around homes and buildings. It frequently establishes itself in human-made structures and clutter outdoors. The brown widow tends to choose sites that are more exposed than those favored by the black widow, increasing the potential for human interaction.
Preferred Outdoor Locations
The spider is often found in areas such as:
- Under patio furniture.
- In garages, sheds, or storage closets.
- Recessed hand grips of plastic garbage cans.
- Under eaves.
- Empty containers like buckets or nursery pots.