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brown widow and black widow spiders

side-by-side image of two spiders. at left, a brown widow, hanging vertically in webbing, showing its underside toward the viewer. the spider is dark brown to black in color, with an bright orange blotch on the bottom of its abdomen. at right is a black widow spider, hanging vertically on a stick, viewed from the side. the spider is dark black in color with a bright red splotch visible on the underside of its abdomen.

Black widow spiders have earned a fearsome reputation for their venomous bite. But in parts of the southern United States these spiders have much to fear themselves—from spider relatives who really don’t like their company. In the past couple decades, researchers have noticed southern black widow spiders (Latrodectus mactans, adult female shown at right) commonly being displaced by the brown widow (Latrodectus geometricus, adult female at left), a fellow species in the same genus. But new research suggests this isn’t a just simple case of one species winning the competition for food or habitat. Instead, a study shows brown widow spiders have a striking propensity to seek out and kill nearby black widows. (Note: Images are not shown to matching scale and thus do not reflect relative sizes of the two spiders.) (Photo by Louis Coticchio)

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