Black Widows are found in Wisconsin. The species most commonly documented is the Northern Black Widow (Latrodectus variolus). The female possesses a neurotoxic venom, a characteristic that sets it apart from the vast majority of harmless spiders found in the region.
Presence and Distribution in Wisconsin
The Northern Black Widow is a native species, but its presence is generally rare and isolated. Wisconsin is the northern edge of its natural range, which limits its ability to thrive in colder northern regions. Documented sightings are concentrated primarily in the central and southern portions of the state, particularly in the east-central counties bordering Lake Michigan, such as Door County, which has historically recorded the most sightings.
Away from the lake, the spiders have also been found in microclimates of the southwestern counties, specifically in prairie areas like Sauk, Crawford, and Grant counties. These spiders seek undisturbed, secluded habitats that provide shelter, such as wood piles, under rocks, in tree stumps, and occasionally in dry, quiet areas of structures like basements or crawl spaces.
How to Identify a Black Widow
Identifying the female Northern Black Widow is straightforward due to its distinct features. The adult female is a medium-sized spider, measuring approximately 10 to 12 millimeters (0.4 to 0.5 inches) in body length, and is characterized by a glossy, jet-black color and a large, globular abdomen.
The most recognized feature is the red or orange-red marking on the underside of the abdomen. For the Northern Black Widow (L. variolus), this marking is often broken into two separate triangular spots, rather than the complete hourglass shape seen in other species. Females may also display small red spots on the top side of the abdomen.
In contrast, the male is significantly smaller and more slender, usually brown or gray, and may have faint white stripes or spots instead of the clear hourglass. The web is an irregular, three-dimensional mass of strong, sticky silk, often spun in a dark, sheltered crevice close to the ground.
Understanding the Bite and Medical Risk
The female black widow is non-aggressive and typically only bites defensively when accidentally pressed against human skin. The bite may initially feel like a slight pinprick or go completely unnoticed. The symptoms that follow are collectively known as latrodectism, a syndrome caused by the neurotoxin in the venom.
Neuromuscular effects usually begin within an hour and include generalized muscle pain and severe cramping, which often starts near the bite site and spreads to the abdomen, chest, or back. Other systemic effects can involve nausea, vomiting, and localized sweating around the bite area.
While the symptoms can be intense and last for several days, fatalities are uncommon. Medical attention is recommended, particularly for individuals who are very young, elderly, or have pre-existing health conditions, to receive supportive care. Treatment focuses on managing pain and using muscle relaxants to alleviate the cramping; antivenom is available but rarely required.