Black Widow Spider (Latrodectus mactans)

Identification

The southern black widow is a medium-sized, glossy-black spider with a spherical abdomen. Females (the medically significant sex) have a body about ½ inch long with a leg span of 1–1.5 inches. The identifying mark is a red or orange hourglass shape on the underside of the abdomen — you need to see the belly, which means the spider is usually in its web when you identify it. Males are much smaller with brown and white markings and are not medically significant.

Black widow webs are messy, irregular, and extremely strong for their thickness — catching your hand in one feels noticeably different from walking through a typical garden spider web.

Where Black Widows Live in the RGV

Black widows prefer dark, sheltered, ground-level locations. On Brownsville properties, we find them in a handful of predictable spots: under meter boxes, inside electrical junction boxes, beneath stored lumber and landscape timbers, in the backs of seldom-opened sheds and garages, under outdoor furniture cushions, and in the cinderblock voids of block fences and walls.

They are outdoor spiders that occasionally come inside — typically in garages, laundry rooms, and ground-floor utility areas rather than living spaces. Properties with significant ground clutter, woodpiles, and debris accumulation — common on larger rural lots in San Benito and La Feria — harbor larger populations.

Bite Danger

Black widow venom is neurotoxic — it affects the nervous system rather than destroying tissue, the opposite of the brown recluse’s necrotic venom. Bite symptoms include intense pain at the site, muscle cramping (particularly in the abdomen and back), nausea, sweating, and elevated blood pressure. Symptoms can persist for 24–72 hours. Children, elderly individuals, and people with cardiovascular conditions face higher risk of serious complications. Medical attention is recommended for any confirmed black widow bite.

Reducing Black Widow Risk

Clear ground-level debris, woodpiles, and stored materials away from the house perimeter. Wear gloves when reaching into dark outdoor storage areas. Shake out shoes and gloves that have been stored outdoors. Professional perimeter treatment combined with habitat reduction effectively manages black widow populations on residential properties.