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Poisonous Spiders

St Andrews Cross SpiderSt Andrews Cross Spider
Photo: T. Taylor
Some 2,900 species of spiders live in Australia, but only few of these can harm humans and only three species are known to have caused deaths. While from a scientific perspective all spiders have toxins, most spiders are very small and their bite cannot even penetrate the human skin. Of those which are large enough, most don't have a venom potent enough to cause more than a mild local reaction similar to a bee sting. The largest spider in Australia - and the second largest in the world - for example is the Huntsman spider which can reach a leg span of 30 centimetes, the size of a dinner plate. But apart from scaring the hell out of you, it won't do much harm. And there are even some colourful and quite beautiful spiders, like the St. Andrew's Cross Spider which again is harmless for humans.

Keep in mind that spiders have developed over millions of years and are much older than humans. In the case of the so called primitive spiders which are usually more venomous, this time span is as long as 350 million years. Yes, spiders have inhabitet this planet more than 100 million years before the first dinosaurs and they still do. So whatever venom these spider might have, it is never directed at humans and humans are much larger than the natural prey and the venom needs to be extremely potent to cause harm. The few cases where this is the case are nothing but a - from our perspective very unfortunate - coincident.

Sydney Funnel-web Spider (Atrax robustus)

Photo of male and female Sydney Funnel-web spiderMale (top) and female (bottom) Sydney Funnel-web spiders
(Photo: Wikipedia)
Known as the world deadliest spider, the Sydney Funnel-web Spider can indeed kill even a strong and health adult, however only 13 fatal events have been recorded at all and none since the antivenom was developed in 1981. The habitat extends north to south between the Hunter River and Illawarra Region and from the coast to the Blue Mountains.

Body length is between 1 and 5 cm with females being slightly larger than male spiders. Both genders are glossy and colour ranges from blue-black over black and brown or dark-plum coloured.

Funnel-web spiders are highly aggressive and easily provoked. If they bite, they tend to keep a grip on their victim and strike multiple times. While female spiders spend most of their time in their burrows, males wander around - especially during the warmer months - searching for females to mate with. Unfortunately that brings males occasionally into houses where they pose a threat to humans. Especially so, because the venom of the male spider contains a special component which makes it fatal for humans and monkeys while other mamals like cats or dogs are relatively resistant. The female spider's venom is still potent but not deadly.

Symptoms of envenomation include severe pain at the site of the bite and within minutes these are followed by goose bumps, sweating, tingling around mouth and tongue, twitching (initially of face and in between the rips), salivation, watery eyes, elevated heart rate and blood pressure. As systemic envenomation progresses symptoms include nausea, vomiting, shortness of breath (caused by airway obstruction), agitation, confusion, writhing, muscle spasms (including grimacing) and finally pulmonary oedema, metabolic acidosis and extreme hypertension which leads to the final stage where pupils are often dilation and fixed, muscles twitch uncontrollably all over the body and finally the elevated intracranial pressure leads to death.

If bitten by a funnel-web spider (or any large black spider if you are not certain what kind of spider it was), apply a pressure bandage as I describe this in the first aid section and seek medical help immediately. The symptoms of systemic envenomation start usually in less than 30 minutes. Applying a pressure bandage might delay this and buy you some time.

Northern Tree Funnel-web Spider (Hadronyche formidabilis)

With 4-5 cm body size it is slightly larger than the Sydney funnel-web spider and almost as venomous. As the name suggests, it lives further north in Queensland and New South Wales and unlike the Sydney funnel-web spider, it does not live in burrows in the ground but on trees.

Everything else I have said about the Sydney funnel-web spider also applies to this species.

Redback Spider (Latrodectus hasseltii)

Photo of Redback spiderRedback Spider
Photo: Wikipedia
Redback Spiders belong to the family of the widow spiders and are closely related to the famous black widow.  The are common all over Australia. They survive in conditions below freezing point to well above 40 degrees. Female spiders have a rounded body of approximately 1 cm length with a prominent red stripe on the back. Juvenile spiders have additional white markings. Males are much smaller with only 3-4 mm body length. It is not known if the male spider's fangs can actually penetrate the human skin but they might actually be unable to do so, because all known envenomations have been caused by female spiders.

While the venom can be dangerous, the symptoms only develop over a time of 24 hours. The initial stages include severe pain and swelling at the site of the bite, nausea and vomitting and muscle cramps in abdomen, back and tights. As the onset of symptoms is so slow, no fatalities have been recorded since antivenom became available in 1956.

If bitten, you should apply a pressure bandage as described in the first aid section and seek medical help. In many cases no treatement might be necessary, but better to be safe than sorry.

Want to know more?Books and DVDs I can recommend

Dangerous Creatures of Australia

On almost 100 pages the author gives an introduction to the most dangerous creatures in Australia. Given the limited space this book can only provide a brief overview.

Spiders of Australia: An Introduction to Their Classification, Biology & Distribution

A comprehensive guide to Australian spiders, their identification and classification.

Spectacular Snakes of Australia

The book presents the snakes of Australia and unlike other books has a particular focus on the photographic presentation. Ideal for every friend of snakes and reptiles.

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