Australia’s snakes may be scary, but I think its spiders are definitely worse: these guys are much more likely creep into your bedroom and get you when you’re sleeping, or hide somewhere in your house just waiting to bite you if you inadvertently disturb them…
Sydney Funnel-Web Spider
The Sydney funnel web spider has an LD50 of 0.16mg/kg – making it more deadly than most snakes – and is regarded by many authorities to be the most dangerous spider in the world.
Personality: funnel-webs are scary-looking things, with a body length of up to 7cm. They can be extremely aggressive if they feel threatened. Females spend most of their long lives hiding in their silky burrows, only emerging to grab passing prey, and therefore rarely cause any problems. Males, however, spend most of their time wandering around trying to find females to mate with. This means they regularly end up in houses, cars, shoes, clothes and many other places where unsuspecting humans might disturb them. They are attracted to water and often fall into swimming pools, where they can survive underwater for up to 24 hours and subsequently bite anyone who tries to remove them. They are most commonly found within a 100km radius of Sydney.
Venom: contains an excitatory neurotoxin known as delta-atracotoxin or robustoxin. Robustoxin acts by slowing the inactivation of voltage-gated sodium channels and stopping them from closing properly. This results in continuous acetylcholine release, overstimulation of the neuromuscular junction, widespread overexcitation of the nervous system and ultimately weakness and paralysis resulting from depletion of neurotransmitter reserves.
Bite: funnel-web fangs are large (5-7mm long) and powerful – they can penetrate soft shoes and even toenails. Bites are usually extremely painful due to the large puncture marks and the acidic nature of the venom. Each bite delivers only a small amount of venom (about 0.14mg), but funnel-webs tend to cling tightly to their victim and inflict multiple bites. Despite this, the rate of significant envenomation is only 10-20%.
Clinical features: the venom can take effect extremely rapidly, causing death in under an hour. There may be symptoms of systemic envenomation as described previously. Excitatory neurotoxicity manifests itself as muscle fasciculations (characteristically affecting the tongue in early stages) and autonomic symptoms such as perioral tingling, sweating, salivation, lacrimation, piloerection, tachycardia, malignant hypertension and pulmonary oedema. Severe envenomation may progress to involve convulsions, fixed dilatation of the pupils, confusion, loss of consciousness, raised intracranial pressure and death.
Redback spiders are close relatives of the infamous Black Widow. This deadly heritage is reflected by their extremely potent venom, with its LD50 of 0.90mg/kg.
Personality: female redbacks are much larger than males, but their bodies are still only about 1cm in diameter. Despite their small size they can easily prey upon lizards, mice and even small snakes. The females perform sexual cannibalism during mating. Unlike funnel-webs, it is the female redback which causes most problems with bites. Although they are common in urban areas they rarely stray from their messy webs, so humans are much less likely to encounter them unexpectedly unless the webs are located in frequently-visited places such as letterboxes, garages or garden furniture.
Venom: contains an excitatory neurotoxin called alpha-latrotoxin. It interacts with receptors on the membranes of presynaptic neurones and becomes inserted into the membrane, forming a pore which is permeable to calcium ions. The subsequent calcium ion influx triggers massive neurotransmitter release, and neurotransmitters can also leak passively out of the pores in the membrane. This results in initial overstimulation of the nervous system, followed by muscle weakness or paralysis once neurotransmitter reserves become exhausted. The pores also leak water, causing nerve terminal swelling and oedema.
Bite: redbacks only have tiny fangs, so bites to humans are often quite ineffective. Even if the spider does manage to give you a decent bite, the rate of significant envenomation is less than 20%. Because the puncture marks are so small, pain is often delayed by up to half an hour.
Clinical features: redback bites progress very slowly and symptoms can persist for days. Once the venom begins to take effect, the pain around the bite can soon become excruciating. Pain then spreads proximally to involve the whole limb, regional lymph nodes and eventually the whole body, resulting in a variety of symptoms such as headache, aching joints, chest pain and abdominopelvic pain. Sweating, piloerection and swelling are also characteristic features and follow the same pattern, beginning around the area of the bite before becoming generalised and excessive. Other common features include muscle cramps, pyrexia, nausea, tachycardia, and hypertension. Severe cases may progress to muscle weakness and paralysis. These symptoms are virtually identical to those caused by black widow bites, and form the syndrome known as lactrodectism.
Mouse spiders are often mistaken for funnel-webs: they are generally considered much less deadly, but their bites are nasty and can sometimes have serious consequences.
Personality: mouse spiders are pretty scary but not as big as funnel-webs; their bodies can be up to 3cm in length. Females are completely black, whereas males have impressive blue and red colouration. Females live in deep burrows covered with a trapdoor – which can be opened quickly to grab passing insects – and spend most of their time guarding their eggs or raising their little spiderlings. Males wander in search of females, and die after mating. Both can be aggressive and will bite if provoked, but they tend to avoid heavily populated areas so encounters with humans are less common.
Venom: the venom of the Eastern mouse spider has been found to contain compounds similar to robustoxin, the deadly excitatory neurotoxin found in funnel-web spider venom. Preliminary tests in mice have found that mouse spider venom may actually be more lethal than funnel-web venom!
Bite: they have large fangs which inflict a deep painful bite. The rate of significant envenomation is unknown but is likely to be very low: it is believed that most mouse spider bites are “dry” bites devoid of venom.
Clinical features: most people who are bitten will only suffer the distress of a vicious spider attack and the effects of a painful bite. However, in rare cases bites have been known to cause symptoms very similar to funnel-web bites, with rapid onset of excitatory neurotoxicity and autonomic dysfunction. As a result, it is vital that all patients seek medical attention as soon as possible. Medical staff should treat mouse spider bites as funnel-web bites until proven otherwise.
White-tailed spiders are generally considered to be relatively harmless, but there is ongoing debate as to whether their bites can cause necrotising arachnidism (which is unfortunately just as nasty as it sounds).
Personality: female white-tailed spiders are larger than males, with a body length of about 2cm. They are hunting spiders and therefore do not build webs, but instead wander around at night looking for food. They like to eat other spiders (mainly house spiders, but redbacks too!) which can always be found in bountiful quantities in and around human dwellings. They will happily find shelter under almost anything in the home, especially bedsheets and things like shoes, towels and clothes that have been left on the floor. This habit of hiding in inconvenient places means that white-tailed bites are fairly common.
Venom: analysis of white-tailed spider venom has so far yielded no evidence of components that could cause major harm to humans. The venom of male spiders contains small amounts of histamine and noradrenaline, which explains the localised effects experienced after a bite. Importantly, there is no evidence that the venom contains any toxins that could cause skin necrosis.
Bite: white-tailed spider fangs are only small and often cannot penetrate human skin. When bites do occur they are usually painful. Their fangs have been found to carry Mycobacterium ulcerans, which could be a contributing factor in reported infections and skin ulcers following a bite.
Clinical features: immediate localised pain is followed by erythema, swelling and itch around the area of the bite. In rare cases patients may develop systemic features such as malaise, nausea, vomiting or headache. A number of cases have been reported of white-tailed spider bites causing necrotising arachnidism; this is characterised by blistering, ulceration and skin necrosis which can be severe and distressing. However, in many of these cases the bite was unwitnessed and the white-tailed spider could not be reliably identified as the culprit. In a prospective study of 130 confirmed white-tailed spider bites in Australia there were no cases of infection or ulceration, but another study of 15 cases of ulceration or necrosis following spider bites reported that white-tailed spiders were responsible in at least 3 cases. The presence of destructive M. ulcerans in their fangs provides a plausible explanation for the occasional case of skin ulceration, but generally white-tailed spider bites heal uneventfully with little need for medical attention.
Managing a spider bite
Generally it’s a good idea to try to catch the spider if possible, as there are no venom identification methods available for spider bites and it is important to know the species responsible so that interventions can be made quickly if required. If you cannot catch the spider, try to remember features such as size, shape, colour, and location so you can describe it to medical staff later. Appropriate first aid interventions vary depending on the type of spider and degree of risk: if the spider is definitely non-lethal (e.g. a white-tailed spider) they can usually be managed at home with simple wound care, but if there is ANY DOUBT as to the species responsible immediate medical attention should be sought.
Two reassuring things to remember are that most spider bites do not result in significant envenomation, and effective antivenoms are readily available.
Funnel-webs & mouse spiders
- NEUTRALISE THE SPIDER. Remove it if it is still attached to the patient, and ensure it is no longer a threat before continuing – try to catch it, but squish it if you have to. Put it in a jam jar or other container to take to the hospital for identification.
- Get someone to call an ambulance (dial 000 in Australia).
- Reassure the patient and persuade them to LIE DOWN AND REMAIN AS STILL AS POSSIBLE (muscle contractions hasten the absorption and spread of venom through the lymphatic system).
- Do not interfere with the bite wound in any way.
- Remove jewellery and other items from the bitten limb. This prevents a “tourniquet effect” from occurring if the limb becomes oedematous later.
- DO NOT APPLY A TOURNIQUET or attempt to cut/suck out the wound. The bitten limb should be dressed with a broad bandage applied over the wound area at moderate pressure – being careful not to disrupt blood flow to the extremities – and extended in both directions to cover as much of the rest of the limb as possible. This should be applied over clothing as the patient needs to be kept as still as possible. Bites to the head, neck and torso are slightly more tricky: apply firm local pressure if possible.
- After dressing the wound, immobilise it as best you can using a splint or sling.
- Be vigilant in monitoring the patient for any signs of deterioration, especially breathing difficulties, paralysis, loss of consciousness or cardiovascular collapse.
- Avoid any oral intake – if transport to a hospital is likely to take several hours, clear fluids may be given to maintain hydration.
- Await transport to the nearest medical facility. If you are in an isolated area or emergency service access is likely to be difficult, the patient should be conveyed or carried to a more convenient location whilst remaining as immobile as possible.
Redbacks & white-taileds
Generally as above, but with the following modifications:
- DO NOT USE A PRESSURE BANDAGE. The pain associated with bites from these spiders can be very severe, and will only be made significantly worse by the application of a pressure bandage. Also, the slow-spreading nature of their venom means that a pressure bandage is unlikely to be particularly helpful.
- APPLY A COLD ICE PACK to the wound to relieve pain and help keep the patient calm and still.
- If the spider was definitely non-lethal (e.g. a white-tailed spider) some sources say oral analgesics like paracetamol are also appropriate to help control pain. Oral antihistamines can also help relieve itch and swelling.
Effective antivenoms are available to funnel-web and redback spider venoms, and should be given to any patient with signs of systemic envenomation. Funnel-web antivenom has also been effective in treating severe cases of mouse spider envenomation in the past. Although most antivenoms are administered intravenously, it is currently recommended that redback antivenom be given intramuscularly because the small amounts of venom involved do not necessitate an IV dose in most cases. It is important to remember that antivenoms are derived from powerfully immunogenic animal antibodies, so there is a risk of allergic reactions including anaphylaxis and delayed-onset serum sickness. For more on antivenoms, click here.
Some reassuring statistics
- The last recorded death from a venomous spider bite in Australia was in 1979: since then antivenoms have prevented any fatalities.
- In Australia up to 4000 people are bitten by venomous spiders each year, but only about 250 of these will require treatment with antivenom.
- Most spiders won’t bite you unless you provoke or frighten them. If you do accidentally manage to piss one off and need to defend yourself, just remember, in a battle of man versus spider, you’re much more likely to win.