The Redback Spider (Latrodectus hasselti) is a medically significant arachnid belonging to the genus Latrodectus, which also includes the notorious Black Widow spiders. Common throughout Australia, the species thrives in urban and disturbed environments where it frequently comes into contact with people. While its bite is rarely fatal since the introduction of antivenom, it causes a painful and prolonged illness known as latrodectism.
Identifying the Redback Spider
The female Redback Spider is responsible for almost all bites requiring medical attention, as the male is significantly smaller and its fangs cannot penetrate human skin. An adult female is easily identified by her globular, pea-sized abdomen and slender legs, reaching about one centimeter in length. Her body is deep black, often marked with a prominent orange or red longitudinal stripe on the upper side of the abdomen.
This distinctive red stripe sometimes appears broken, and the underside of the abdomen typically displays a red or orange hourglass-shaped marking. In contrast, the male Redback is tiny, measuring only about three to four millimeters in length, and is light brown with less distinct red or white markings. Juvenile females are also smaller and may have additional white markings on their abdomens before maturing.
Redback Spiders prefer dry, sheltered environments, often constructing their webs close to human habitation. They spin an untidy, tangled web with sticky lines that reach down to the ground, often building them in sheds, garages, under eaves, in junk piles, or beneath outdoor furniture. The spider is largely nocturnal and remains within this web structure, which is a common location for accidental contact.
Symptoms of Envenomation
The venom injected by the female Redback Spider contains a potent neurotoxin called alpha-latrotoxin, which acts on the nervous system. This results in a clinical syndrome called latrodectism, characterized primarily by immediate and escalating pain at the bite site. The initial pain often intensifies over the following hour and can spread proximally up the affected limb or area.
Accompanying the local pain, a localized patch of sweating around the bite site is a highly characteristic sign of Redback envenomation. As the neurotoxin spreads, systemic symptoms may develop, including widespread sweating, headache, and general malaise. Some individuals experience nausea, vomiting, abdominal pain, or chest pain, which can be severe enough to mimic other serious medical conditions.
Other systemic effects include muscle weakness, muscle spasms, and elevated blood pressure and heart rate. While bites are rarely life-threatening, the symptoms can persist for several hours, days, or even weeks in untreated cases. Children and the elderly are considered more susceptible to severe systemic effects from the neurotoxic venom.
First Aid and Clinical Management
Immediate first aid for a suspected Redback spider bite focuses on symptom relief. First, remain calm and clean the wound thoroughly with soap and water to minimize the risk of infection. Applying a wrapped cold pack or ice pack directly to the bite site can help relieve the local pain and swelling.
Unlike first aid for some other venomous bites, it is important not to use a compression bandage or restrict blood flow for a Redback bite. Using a pressure immobilization technique can intensify the localized pain, which is a significant feature of latrodectism. Medical attention should be sought promptly, especially if the victim is a child or if symptoms are severe or spreading.
In a clinical setting, treatment centers on pain management, although simple analgesics are often ineffective against neurotoxic pain. Antivenom is available and typically reserved for cases involving significant or persistent local pain, or when systemic symptoms such as severe sweating, nausea, or muscle spasms develop. The antivenom is safe and effective, neutralizing the circulating neurotoxin, and can be administered even days after the initial bite.