Many people associate spiders with red marks on their backs with danger. While this often points to a specific well-known species, red markings can vary in location and indicate different threat levels. This guide explores spiders featuring red markings, focusing on the black widow and other species with similar coloration.
Identifying the Black Widow
The spider most commonly associated with a red mark is the black widow, particularly the female, known for its distinctive red hourglass shape. This marking is found on the underside of its glossy black, rounded abdomen. An adult female black widow ranges from 8 to 13 mm (0.31 to 0.51 inches) in body length.
Several species of black widow exist in North America, including the Southern black widow (Latrodectus mactans), Northern black widow (Latrodectus variolus), and Western black widow (Latrodectus hesperus). The Southern black widow has a complete hourglass marking. The Northern black widow’s hourglass can be incomplete or separated into two distinct spots on the underside, and it may also have red spots along the top of its abdomen. The Western black widow features an hourglass mark on its underside, which can be red, yellow, or white. These spiders prefer dark, secluded areas for their irregular, tangled webs, such as woodpiles, garages, and basements.
Other Red-Marked Spiders
While black widows are the most recognized, other spider species also exhibit red markings, which can sometimes lead to misidentification. The Redback Spider (Latrodectus hasselti), a close relative of the black widow, has a prominent red stripe along the top of its abdomen and an hourglass mark on its underside. This distinct red stripe helps differentiate it from most black widow species.
Another spider with a red marking is the Red-backed Jumping Spider (Phidippus johnsoni). This species is smaller, around one centimeter (0.4 inches) in body length, and has a bright red abdomen. Female Red-backed Jumping Spiders may have a black stripe down the center of their red abdomen, while males have an entirely red abdomen. These spiders are harmless to humans and are recognized by their squat body and short legs.
Understanding Spider Bites
Spider bites, particularly from the black widow, are rarely fatal but can cause medically significant symptoms. Only the female black widow spider is capable of biting humans and injecting venom. The venom, a neurotoxin, affects the nervous system and can cause various symptoms.
Initial symptoms of a black widow bite include a sharp, pinprick-like pain, followed by a dull ache, swelling, and redness at the bite site. Within 30 to 60 minutes, severe muscle cramps and spasms can develop, spreading from the bite area to the abdomen, back, and chest. Other symptoms include nausea, vomiting, sweating, headache, and increased blood pressure.
Symptoms improve within two to three days, though discomfort can persist for several weeks. Medical attention is advised if a black widow bite is suspected, especially for children, the elderly, or individuals with compromised health. Treatment involves pain relievers, muscle relaxers, and antivenom. Bites from other red-marked spiders like the Red-backed Jumping Spider are not medically significant, causing mild, localized pain or swelling.
Prevention and Safety
Minimizing encounters with spiders, especially those that can inflict a painful bite, involves simple proactive measures around the home and garden. Spiders seek shelter in dark, undisturbed areas, so reducing clutter indoors and outdoors can deter them. This includes clearing woodpiles, old furniture, and debris where spiders reside.
When working in areas where spiders are present, such as gardening, cleaning out garages, or moving stored items, wearing gloves and long sleeves can provide protection. Shaking out shoes and clothing before putting them on is also a good practice. Sealing cracks and crevices around the foundation, windows, and doors of a home can help prevent spiders from entering.