What is Funnel-Web Spider Toxicity?
There are over 40 types of funnel-web spiders, the majority of which are found exclusively in Australia. In particular, three types of these spiders – the Hadronyche, Illawarra, and Atrax – are uniquely found in Australia. The Sydney Funnel-Web Spider, also known as the Atrax robustus, is responsible for most deaths caused by funnel-web spider venom.
These spiders are mostly found along the east coast of Australia. Funnel-web spiders can be described as medium to large in size, with bodies that range from brown to black in color. Some of these spiders, specifically the ones that live in trees, can grow up to 4 to 5 cm long. The Northern Tree Funnel-Web Spider is the largest among these species.
The name “funnel-web spider” comes from their method of hunting. They spin burrows shaped like a funnel to catch their prey. Often, you can find these spiders in cool and sheltered habitats such as rock gardens, shrubberies, and even under logs. Some of them live on trees, possibly several meters off the ground. Bites from a Sydney Funnel-Web Spider can be fatal, though only one death has occurred since 1981, likely due to advances in first-aid techniques and the development of antivenom.
Funnel-web spiders are known for their strong, sharp fangs that can even penetrate fingernails and soft shoes making them the most dangerous spiders in the world. The Sydney Funnel-Web Spider waits just inside the entrance of its burrow, which is designed like a small hallway or vestibule. There, it feels vibrations along the silk lines of its web and uses its venom to immobilize its prey.
What Causes Funnel-Web Spider Toxicity?
There are 36 species of Funnel-Web Spiders (FWSs) native to Australia, and they are identified based on differences in their body structure. Additionally, there are 38 related species that are not found in Australia and belong to the Macrothele genus. Most FWSs live on the ground, including well-known species like Atrax robustus, better known as the Sydney FWS, and Hadronyche infensa, also known as the Toowoomba FWS. However, some like Hadryonyche cerberea (Southern tree-swelling FWS) and Hadronyche formidabilis (Northern tree-dwelling FWS), live in trees. Studies suggest that tree-dwelling species are more likely to cause severe bites compared to ground-dwelling species. Out of all these spiders, only six species have been found to contain a specific poison called δ-hexatoxins.
All bites from FWSs are serious and potentially life-threatening, even though only about 10% to 15% actually contain venom. The venom is highly toxic, so all FWSs are considered dangerous. In case studies where the spider’s gender was identified, it was found that the male FWS was responsible for all lethal bites. Male FWSs are generally more active during the night and have been known to enter houses.
The venom from an FWS bite can take effect very quickly. A study showed that on average, it took only about 28 minutes for symptoms to appear. There were only two cases where it took longer than two hours for symptoms to show, both of which had immobilizing pressure bandages applied immediately on the bites. The venom can cause death in a short time span – within 15 minutes for small children, and up to three days in adults. Younger people and those with existing health conditions are at a higher risk of dying from an FWS bite.
Risk Factors and Frequency for Funnel-Web Spider Toxicity
There’s not a lot of research on Funnel-Web Spider (FWS) bites. However, a study done in 2005 identified 198 possible FWS bite cases from 1999 to 2003. Out of these, 138 were confirmed FWS bites, and 77 of them had caused serious venom poisoning. This severe venom poisoning was mostly caused by three spider species found only in New South Wales and southern Queensland.
- Hadronyche cerberea was responsible for 75% of the cases,
- H. formidabilis for 63%, and
- Atrax robustus for 17%.
Antivenom was used to treat 75 patients, including 22 children. It effectively treated 97% of the positively identified cases. The FWS antivenom did have some side effects. These included mild systemic inflammation, severe inflammation requiring an adrenaline injection, and a delayed reaction resembling a sickness caused by foreign proteins in the blood. Despite this, the researchers concluded that the FWS antivenom was safe and effective. It caused severe allergic reactions only in rare cases.
Lastly, the researchers found that cases of true necrotizing arachnidism—tissue death caused by spider venom—seemed to be quite rare.
Signs and Symptoms of Funnel-Web Spider Toxicity
If a person thinks they’ve been bitten by an FWS (Funnel Web Spider) but didn’t see a big black spider, it’s unlikely that’s what happened. One black spider people sometimes confuse with the FWS is the redback spider, also known as the Australian black widow, which has a red mark on its back. When examining the affected person, health professionals need to know where the bite took place.
What does an FWS bite do? Initial symptoms can include feeling strange sensations on the face, feeling sick, sweating excessively, drooling, and difficulty breathing. Some people may also become confused, agitated, and may eventually lose consciousness. Further complications include irregular heartbeat, high blood pressure, dilated pupils, twitchy muscles, fluid build-up in the lungs and brain, and even death from fluid build-up in the lungs or a drop in blood pressure and circulation. It’s important to act fast, because these symptoms can start within minutes of the bite. However, methods to reduce the flow of venom, such as pressure immobilization, can delay symptoms for a few hours.
A person who’s been bitten by an FWS might have marks from the spider’s fangs near the painful area. There might be some bleeding, but significant swelling or redness are not common. There’s a risk of developing heart and nervous system complications from an FWS bite, so these should be carefully looked at and properly recorded to guide the right treatment.
- Strange sensations on the face
- Feeling sick
- Excessive sweating
- Drooling
- Difficulty breathing
- Confusion
- Agitation
- Loss of consciousness
- Irregular heartbeat
- High blood pressure
- Dilated pupils
- Twitchy muscles
- Fluid build-up in lungs and brain
- Potential death from fluid build-up in the lungs or a drop in blood pressure and circulation
Testing for Funnel-Web Spider Toxicity
If you’re bitten by a spider known as the brown recluse or “fiddleback” spider (FWS), doctors can determine if you were poisoned by the spider by examining your symptoms and the site of the bite, especially if the bite happened in a known habitat for these spiders. There isn’t a specific lab test that confirms an FWS bite. But, doctors can run other tests to rule out other health conditions the bite may cause and see the extent of any organ damage that may have happened from the bite.
For these tests, doctors may take a complete blood count to check overall health and a basic metabolic panel to check the body’s chemical balance and metabolism. They may also test a blood protein called creatinine kinase to examine kidney function, the balance of the body’s electrolytes, and to find any evidence of muscle breakdown, which is medically called rhabdomyolysis.
Gasing the levels of oxygen and carbon dioxide in your blood can help understand any alterations in your body’s acid-base balance. Doctors can also run coagulation studies to check if the spider venom is causing abnormal blood clotting throughout your body. Other tests may include a troponin test to measure levels of these proteins that can indicate damage to your heart, an electrocardiogram (ECG) to check your heart’s electrical activity, and a chest x-ray.
Treatment Options for Funnel-Web Spider Toxicity
If you’re bitten by a large, dark-colored spider in areas where Funnel-Web Spiders (FWS) are commonly found, it’s safest to treat it as a FWS bite. Bites from these spiders can lead to severe and quickly worsening symptoms.
First-aid treatment for suspected FWS bites includes cleaning the bite area with soap and regular tap water, then applying a special bandage known as a pressure-immobilization bandage. This involves wrapping a bandage with light pressure around the affected area and keeping it still, like how you’d use a splint. Keeping the affected area still and under pressure can help limit the spread of the spider’s venom in your body and keep it from affecting a larger area. Some research even indicates that this method can help neutralize the spider’s venom where the bite happened.
You should seek emergency medical help as soon as possible after an FWS bite. It’s crucial to keep the pressure-immobilization bandage in place until a healthcare professional in an emergency department can check you. Early removal of the bandage could allow the venom to spread throughout your body quickly, leading to rapid worsening of symptoms. Before the bandage is taken off, you should be connected to monitoring equipment to track your heart and lung functions, and a healthcare professional should have established intravenous (IV) access (a “line” into one of your veins).
FWS antivenom, a medication that fights the venom within your body, is the primary treatment for people bit by this type of spider whose venom has spread throughout their bodies. But, other ways of supporting your health may also be necessary. Healthcare professionals typically give antivenom as soon as signs of venom spread are observed. If you don’t show symptoms of venom spread, you should still be closely monitored for 4 to 6 hours from the time you were bit or from when the pressure bandage was removed. If you only have symptoms in the area around the bite after appropriate monitoring periods, you most likely wouldn’t need antivenom. If you don’t develop symptoms indicating that the venom has spread to your body after this monitoring period, you may be discharged.
To alleviate pain caused by the bite, you will be given pain-relieving medication. Sometimes, medications called opioids, which are often used for severe pain, might be necessary.
FWS antivenom, or FWSAV, was developed in 1981 and has successfully been used to treat severe cases of FWS bites. The antivenom is made of elements from the defense systems of rabbits against FWS venom. The medication comes in small containers called ampules. When venom seems to have spread, 2 ampules are usually used initially. However, if the bite leads to acute respiratory distress syndrome – a severe lung condition, or causes changes in awareness or behavior, then the initial dose might be doubled to 4 ampules. These doses can be repeated every 15 minutes until the healthcare professional observes improvements in your health. Sometimes, even up to 8 ampules might be used.
It’s important to note that while 2 ampules are usually enough to combat the spread of the venom, continuous symptoms might be due to irreversible effects of the venom. Serious reactions to the FWSAV itself, such as serum sickness (a delayed immune response to certain medications) or anaphylaxis (a severe, potentially life-threatening allergic reaction) have not been reported. This antivenom has proven effective against multiple different species of FWS and is recommended for use for bites from most Australian species of FWS.
What else can Funnel-Web Spider Toxicity be?
If you get bitten and it’s painful, there might be a few potential causes. It could be from another bug, or you could have a skin abscess (a pus-filled bump under the skin) or cellulitis, which is a common skin infection. If you’re feeling sick all over, it’s slightly more complex. The cause could be anything from heart issues like acute coronary syndrome or congestive heart failure, an allergic reaction (anaphylaxis), exposure to toxic substances like organophosphates, nerve agents, or even an overdose on medication. A good talk about your symptoms and a physical check-up can help your doctor figure out if the bite was from a Fiddleback Spider.
What to expect with Funnel-Web Spider Toxicity
A bite from a funnel-web spider (FWS) can be deadly if it goes untreated. However, most confirmed bites from these spiders don’t inject venom and will only cause local reactions in the area of the bite. Despite this, due to the dangerous nature of venomous bites, doctors prefer to err on the side of caution and treat bites as potential venomous bites unless a thorough medical check shows otherwise.
The standard treatment for patients showing signs of systemic, or whole-body symptoms, is antivenom. This particular antivenom can neutralize the venom from a FWS if given promptly, enabling patients to make a full recovery.
Possible Complications When Diagnosed with Funnel-Web Spider Toxicity
People who suffer from a venomous bite from an FWS, but receive antivenom treatment, usually recover fully. The complications from such a bite depend on which parts of the body the venom affects. This could lead to:
- Rhabdomyolysis (a serious condition that can damage the kidneys)
- Kidney failure
- Cerebral edema (swelling in the brain)
- Acute respiratory distress syndrome (severe breathing difficulties)
- Respiratory failure
- Cardiac dysrhythmias leading to cardiac arrest (irregular heart rhythms that can cause your heart to stop)
- Anoxic brain injury (brain damage caused by a lack of oxygen)
Quickly applying a pressure-immobilization bandage and seeking immediate medical help will stop the venom from spreading quickly and can prevent these complications from developing.
Preventing Funnel-Web Spider Toxicity
Funnel web spiders (FWSs) are only found in Australia, so unless you’re traveling to or living in this continent, it’s unlikely you’ll encounter one. If you are in an area where these spiders live, it’s wise to frequently check your clothes, shoes, jackets, and any bedding that’s close to the ground. Be careful if you find any signs of FWS burrows outside like silk lines coming from a central web ring.
These spiders often like to hide in dark, damp places, such as wood or rock piles, so be cautious when you’re working in these types of locations. You can prevent spiders from getting into your home by using weatherstripping and draft protection under doors. Keeping your house tidy and free of clutter also helps keep spiders from making their homes inside.
If you think a FWS has bitten you, you should seek medical help immediately. Applying a pressure immobilization bandage might give you more time to reach medical care. When you go to the hospital, a doctor will quickly assess you and administer antivenom if necessary. If you can, take a picture of the spider because this can aid in confirming what type of spider bite it is. Remember not to bring the spider with you to the hospital or any health facility because this could put others at risk.
