The Redback spider (Latrodectus hasselti) is a venomous spider found throughout Australia and increasingly in other parts of the world. It is recognized for its distinctive appearance and the concern surrounding its bite. A member of the Latrodectus genus, it is closely related to the black widow spiders. Understanding this arachnid’s characteristics and the proper response to a bite can alleviate worry.
Recognizing a Redback Spider
Identifying a Redback spider primarily involves recognizing the female, as she delivers medically significant bites. Adult female Redbacks measure about 10 millimeters in body length, with a spherical, glossy black abdomen. Their most distinguishing feature is a prominent red or orange stripe along the upper side of the abdomen, often accompanied by an hourglass-shaped red or orange streak on the underside. Females also have slender legs, with the front pair appearing longer.
Male Redback spiders are considerably smaller, usually 3–4 millimeters long, and are light brown with less distinct markings, sometimes featuring white spots or a paler hourglass. Their fangs are generally too small to penetrate human skin, meaning male bites are not dangerous. Redback webs are often untidy, consisting of a tangled, funnel-like retreat area from which sticky vertical threads extend to the ground.
Where Redbacks Live
Redback spiders are widely distributed across Australia, adapting well to natural and urban environments. They are commonly found near human residences, thriving in sheltered, dry locations. Typical habitats include sheds, garages, under houses, outdoor toilets, and junk piles. These spiders prefer areas like under outdoor furniture, in logs, or among rocks, where they build their irregular webs.
Their presence is common in urban and disturbed areas, largely due to the lack of major predators in human environments. While native to Australia, Redback spiders have spread to other parts of the world, including New Zealand, Southeast Asia, Japan, the United Arab Emirates, and even some greenhouses in Belgium, often transported via packing crates.
Understanding Redback Venom
Redback spider venom is neurotoxic, primarily affecting the nervous system. Its active component, alpha-latrotoxin, causes the release of neurotransmitters at nerve endings, leading to various symptoms. Bites are often immediately painful, described as a sharp pinprick or burning sensation, with pain intensifying and spreading within minutes to an hour. Local symptoms include swelling, redness, and localized sweating around the bite site.
Systemic symptoms can develop hours later, including nausea, vomiting, headache, abdominal or chest pain, general sweating, and muscle weakness. Hypertension and an increased heart rate can also occur. While Redback bites can be painful, fatalities have become rare since the introduction of an effective antivenom in 1956. Symptoms can persist for hours, days, or even weeks if left untreated, though they typically fluctuate.
Responding to a Redback Bite
Immediate first aid for a Redback spider bite involves applying a cold compress or ice pack to the bite site to alleviate pain. Apply the cold pack for no longer than 20 minutes at a time, allowing the skin to rest before reapplying. Unlike some other venomous bites, the pressure immobilization technique is not recommended for Redback bites, as it can worsen local pain.
Seek medical attention promptly, especially for children, the elderly, or individuals with underlying health conditions, or if severe symptoms develop. Medical professionals may administer pain relief. In cases of severe pain or systemic symptoms, antivenom may be considered. The antivenom, derived from horse plasma, is effective at neutralizing the venom and reversing symptoms. However, many people experience mild enough symptoms that antivenom is not necessary.