Of all the thousands of Australian spiders, arthropods and insects, only three have bites which are capable of causing death - the funnel web (and related atrax species), the red-back spider and the paralysis tick.
The funnel web is a large, black, aggressive spider with massive fangs. Disturbing the spider will usually cause it to rear up on its hind legs, aggressively exposing these fangs. The spider will firmly grip its victim and bite repeatedly - often an horrific experience. Although most commonly found in the north-eastern part of Australia, the Sydney funnel web spider is the only one of 35 species to have definitely caused death; however, bites from other funnel webs have caused serious envenomation and clearly have the potential to cause death. .
The venom of the slightly smaller male spider is about five times stronger than the female. Male funnel webs tend to roam about during summer, particularly after thunderstorms, sometimes wandering indoors. The primary toxic component in funnel web venom is atraxotoxin, it also contains hyaluronidase and other components (GABA, spermine and indole acetic acid).
Atraxotoxin causes acute massive releases of neurotransmitters, causing a multitude of unpleasant symptoms. Dr Ken Winkler, researcher at the University of Melbourne Venom Research Unit notes that the funnel web's venom interferes with the chemicals involved in the transmission of nervous impulses.
"The sympathetic nervous system associated with the 'flight or fight' response is over-stimulated, releasing massive amounts of neurotransmitters," he says.
Unconsciousness, raised intracranial pressure, widely dilated pupils, uncontrolled twitching and death unless artificial ventilation is provided.
eknowhow consultant GP, Dr David Taylor, stresses that a pressure immobilisation technique must be commenced immediately. This involves wrapping the affected area tightly above the sting to prevent the spread of venom through the blood system.
The patient should then be immediatley evacuated to the closest medical facility capable of treating a funnel web bite.
Treatment will require giving antivenom as soon as possible, artificial ventilation and invasively monitoring the patient.
Dr Winkler notes that since the introduction of funnel web anti-venom in the 1980's, no funnel web spider bite fatalities have been recorded in Australia.
Red-back spiders
The adult female red-back is about 2-3cm long, quite black with a distinctive red stripe on its abdomen. The male is much smaller and considered harmless. Neither are aggressive. Red-back venom contains neurotoxins, but works very slowly. Fatalities, even from untreated bites, are rare.
The bite is immediately painful, and pain may affect the whole limb. Sweating is common, as are headaches, nausea, vomiting, abdominal pain, hypertension, and in severe cases, paralysis. Untreated the symptoms worsen over a 24 hour period and may take weeks or months to resolve.
The pressure technique is not recommended for this type of spider bite "it may actually cause local pain to become excruciating. It is better relieved with ice packs."
A red-back specific anti-venom is available and reliable, given to around 250 cases per year. Dr Winkler says the red-back spider anti-venom is the most common spider bite anti-venom administered in Australia.
The white tailed spider
Bites from the white tailed spider have been frequently implicated in the development of a syndrome known as necrotising arachnoiditis. In this particular condition a near painless bite can progress to painful cutaneous blistering and inflammation. The condition can progress to such a state that it requires amputation, however this is rare.
Dr Winkler notes that cutaneous blistering can occur with other spider bites, and indeed conditions, so more research is needed to establish why some individuals develop this response, and others don't.
Treatment of necrotising arachnidism depends on the severity of the condition. If an area of blistering and redness develop, the affected limb should firstly be elevated. At this stage of the infection the use of antibiotics has not been proven to be effective, and is not recommended.
If secondary infection is suspected, blisters may be cultured to check for the presence of mycrobacteria or other bacteria, and anitbiotics prescribed. Lesions should be closely monitored in addition to the patient's temperature and general condition.
Insects
Paralysis ticks
The paralysis tick can be found along the south eastern coastal regions of Australia. It is named so because of a neurotoxin it releases in its saliva which causes progressive, and potentially fatal, paralysis. The tick may often go unnoticed until weakness or ataxia develop.
Dr Winkler notes that the venom of the paralysis tick can cause quite severe allergic reactions in some individuals, who are allergic to the proteins in its saliva. Immediate medical attention is essential for these people.
The first course of action with this type of bite should be to remove the tick from the patient's body. Never grip the body and pull - this action will generally squeeze more venom in, and leave the insect's head firmly stuck in the victim. Several methods for tick removal are available, one of the most effective being to place a pointed pair of scissors underneath the tick's 'shoulders', and levering it out of the skin.
Tick bites are treated with an anti-venom which is administered intravenously. Airway support and ventilation may occasionally be required.
Bees, wasps and ants
Dr Winkler believes this type of bite is generally only problematic in individuals who are allergic to the insect venom.
"In those cases, a sting can be fatal - allergic reactions to wasp stings are the second highest cause of fatality in Australia after snake bites."
In these cases, the pressure and immobilisation technique described above should be applied and the patient immediately bought to hospital.
Bee stings should be scraped off, rather than pulling them out to avoid further venom being squeezed into the blood system. Ice packs applied to the affected area are generally the only treatment required however antihistamines, analgesics and steroids may also be of assistance.
For more information on spider, snake and insect bites contact the Venom Research Unit of Melbourne University on (03) 9344 7753 or their web site. For emergency advice call the Poisons Information hotline 131126 .
Date reviewed: May 11, 2005
