The Redback Spider (Latrodectus hasselti) is a highly venomous arachnid found across Australia and is a member of the widespread widow spider family. The distinction between “poisonous” and “venomous” is important: poisonous organisms release toxins when eaten or absorbed, while venomous creatures, like the Redback, actively inject toxins through a bite. The female Redback produces a potent neurotoxic venom that can cause significant illness in humans.
Recognizing the Redback Spider
The female Redback Spider is the one of concern, recognized by her distinctive physical characteristics. She has a spherical, glossy black abdomen, typically measuring about 10 millimeters long. The most recognizable feature is a prominent red or orange stripe running lengthwise down the upper side of the abdomen. A red or orange hourglass-shaped marking is also often visible on the underside.
The male Redback is dramatically smaller, measuring only three to four millimeters long, and is light brown with less distinct white markings. Since his fangs are too small to penetrate human skin effectively, the male does not pose a medical threat. Redback spiders construct untidy, tangled webs, often with vertical, sticky ‘trap lines’ extending to the ground. They prefer dry, sheltered locations near human habitation, such as sheds, garages, under outdoor furniture, and in letterboxes.
What Happens After a Bite
The bite from a female Redback injects a neurotoxic venom that acts directly on the nerves, leading to a condition known as latrodectism. The primary toxin, alpha-latrotoxin, causes the release and subsequent depletion of chemical messengers in the nervous system. While the initial bite may feel like a small pinprick, intense localized pain typically develops within five to ten minutes and increases over the following hours.
The pain often radiates outward from the bite site, sometimes traveling up the limb or spreading to the abdomen, chest, or back. A highly specific symptom is localized sweating (diaphoresis) around the bite area, often accompanied by piloerection (goosebumps). Systemic symptoms can follow, including headache, muscle weakness, nausea, and vomiting. Although Redback bites can cause severe systemic reactions, the symptoms often progress slowly and are rarely life-threatening since antivenom became available.
Emergency First Aid and Treatment
For a suspected Redback spider bite, the immediate priority is managing local pain. Applying a cold compress or ice pack to the bite site can help reduce pain and swelling. The ice should be wrapped in a cloth and applied intermittently, such as for 10 to 20 minutes at a time.
It is important to avoid using a pressure immobilization bandage, which is commonly recommended for funnel-web spider bites. For a Redback bite, this technique is ineffective due to the nature of the venom’s spread and can intensify localized pain. The victim should be kept calm, and simple pain relievers, such as paracetamol, can be given while seeking medical assessment. Antivenom is available and highly effective, but it is typically reserved for severe cases where pain is unmanageable or significant systemic symptoms, like muscle weakness or severe sweating, are present. Fatalities from Redback bites are extremely rare due to the availability of this specific antivenom.