Mouse spiders (Missulena) are found across mainland Australia, with one species native to Chile. These spiders are confirmed to be venomous, possessing a neurotoxin that can cause serious effects in humans. While bites are relatively uncommon, they should always be treated as a medical emergency due to the potential severity of the venom’s effects.
Physical Characteristics and Distribution
Mouse spiders are thickset, medium-to-large spiders, typically ranging from 10 to 35 millimeters in body length. They are easily recognized by their bulbous head and jaw regions, featuring a broad, smooth, and shiny carapace. Their large chelicerae, or fangs, are capable of inflicting a bite.
A notable feature is the pronounced sexual dimorphism, particularly in color and size. Female mouse spiders are usually stocky and uniformly dark brown or black, spending their entire lives within their silk-lined burrows. In contrast, males are often smaller and more brightly colored, such as the male Red-headed Mouse Spider (Missulena occatoria) which has a bright red cephalothorax and gunmetal blue abdomen.
These spiders construct deep, vertical burrows that can reach up to 55 centimeters deep, often capped with a hinged trapdoor or a silk lining at the entrance. They are found across a wide range of environments, from open forests to semi-arid shrublands. Males leave their burrows during the breeding season to wander in search of mates, which is when they are most likely to be encountered by humans.
Assessing the Danger of Mouse Spider Venom
The venom produced by mouse spiders is neurotoxic, meaning it acts on the nervous system, and shares similarities with the venom of the Australian funnel-web spider. Scientific studies have shown that the venom contains toxins that affect presynaptic transmitter release by modifying sodium channel gating, an action similar to the delta-atracotoxins found in funnel-web venom. The venom from some female mouse spiders has been shown to be potentially as dangerous as that of the Sydney Funnel-web spider in laboratory testing.
Despite the venom’s potential toxicity, recorded cases of severe envenomation in humans are rare, and fatalities have not been documented. Mouse spiders are believed to frequently administer “dry bites,” where no venom is injected, or to use less venom than their funnel-web counterparts. Most bites result in only minor or moderate local effects.
In the event of severe systemic envenoming, the Australian funnel-web spider antivenom has been proven effective against mouse spider venom. This antivenom is typically administered in a hospital setting for serious cases, particularly those involving children. The use of a standard, commercially available antivenom for this species reduces the medical risk associated with a bite.
Symptoms and Emergency First Aid
A mouse spider bite often causes immediate and intense localized pain. This pain may be followed by localized symptoms such as redness, swelling, and sometimes minor muscle twitching near the bite area. However, the potential for systemic symptoms necessitates immediate emergency care.
Systemic effects of envenomation can include severe generalized symptoms and neurological signs. These symptoms may manifest as:
- Profuse sweating, headache, nausea, and vomiting.
- Tingling sensations, particularly around the mouth and tongue.
- Uncontrollable muscle spasms and abdominal pain.
- Elevated blood pressure, especially in children.
Emergency first aid for a suspected mouse spider bite should follow the protocol established for a funnel-web spider bite. Apply the Pressure Immobilization Technique (PIT). This involves placing a broad, firm pressure bandage directly over the bite site and then wrapping a second elasticized bandage firmly up the entire length of the affected limb.
The limb must then be immobilized, ideally with a splint, and the person should be kept as still as possible to slow the spread of the venom. Emergency services must be contacted immediately, and the bite site should not be washed or cleaned, as any residual venom marks may assist medical staff in identifying the spider.