Northern Black Widow

Latrodectus variolus — the northern black widow — is one of three NA black widow species (Latrodectus hesperus — western black widow, already in the Wild Files; Latrodectus mactans — southern black widow; Latrodectus variolus — northern black widow). The species is widespread across the eastern and central US (especially the Appalachian region, the upper Midwest, and southern New England) and southern Canada. Females are 8-13 mm body length (the size of a small grape), shiny jet-black with the species' diagnostic feature: a 'BROKEN' RED HOURGLASS MARKING on the underside of the abdomen. The classic 'black widow hourglass' shape (a single connected red hourglass-or-bowtie shape on the underside) is SPLIT INTO TWO SEPARATE RED TRIANGLES in northern black widows — the upper and lower halves of the hourglass do not connect at the middle. The broken-hourglass pattern is the most reliable field-ID feature for distinguishing northern black widows from the southern and western species (both of which have the classic intact hourglass). Females also commonly show a row of RED-OR-YELLOW SPOTS along the dorsal midline of the abdomen (these spots are typically absent in southern and western black widows). Males are much smaller (4-5 mm), light brown with white markings, and possess only minor amounts of venom (males rarely bite humans and the bites are not medically significant). Like other black widows, the species has POTENT NEUROTOXIC VENOM. The active toxin (ALPHA-LATROTOXIN) binds to specific receptors on vertebrate nerve terminals and causes massive uncontrolled neurotransmitter release at neuromuscular junctions, leading to severe muscle pain, cramping, sweating, hypertension, and other systemic symptoms. Bites are typically not immediately painful (the spider's small fangs cause minimal mechanical trauma), but symptoms develop over 30-60 minutes after envenomation and can persist for 24-48 hours. ANTI-VENOM (Latrodectus immune Fab) is highly effective at reversing symptoms and is the standard treatment for severe envenomation. With modern medical treatment, FATAL BITES ARE EXTREMELY RARE in NA — historical fatality rates were 1-5% before anti-venom was developed in the 1930s, but modern fatality is well under 1%. Females construct distinctive irregular-mesh COBWEBS in dark hidden locations (woodpiles, under decks, in sheds, in basements) and wait at the web for prey. Females are typically NOT AGGRESSIVE toward humans — bites usually occur when a person reaches into a hidden location and accidentally contacts a guarded female. The species is featured in essentially every modern medical textbook discussion of arachnid envenomation.