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The Conversation

  • Written by Ronelle Welton, Scientist AVRU, University of Melbourne

Recent news reports that a man had both his legs amputated after being bitten by a white-tailed spider have again cast this relatively harmless spider in a negative light. Experts have since said amputations may have been wrongly blamed on a spider bite, and authorities now consider a bacterial infection to be responsible for the man’s injuries. Despite this, the damage to the largely harmless white-tail may have been done.

The venom from the white-tailed spider is listed as non-lethal. It has not been shown to cause necrotic ulcers, which could result in the need for amputation. And there has never been any clear evidence necrotising arachnidism – the name give to a syndrome where the skin blisters and ulcerates following spider bites – has been seen in Australia.

There is currently no clinical test to determine if you have been bitten by a spider. And there is no blood or swab test that can be performed to positively identify what spider it is if a bite is suspected. Whether it is a bite from a spider or another insect, the management is the same – most will get better without any medical treatment.

Spiders in Australia

The majority of spiders in Australia are voracious predators of insects. For the most part, they play a useful role in lowering insect numbers.

The venom transmitted through bites of some Australian spiders can cause harm to humans and even be life-threatening. The better known of these are the redback spider (Latrodectus hasselti), and the funnel-web spiders (genera Atrax and Hadronyche). Antivenom is available for both spiders.

Redback spider venom can cause a lot of pain. Advice would be to go to hospital if pain lasts for longer than a few hours and simple pain relief is not helping. Funnel-web spider venom can cause local swelling in addition to increasing heartbeat, salivation, muscle spasms and respiratory distress (trouble breathing).

Without appropriate first aid, quick access to hospital and antivenom, these bites can be lethal. For the “big black hairy” funnel-webs, appropriate first aid needs to be applied and it is advisable to call 000.

image The redback spider is considered one of the most venomous to humans in Australia. graibeard/Flickr, CC BY

Other spiders that have concerning bites include the trapdoor, whistling, sac, ground, orb and huntsman spiders. These may cause milder symptoms such as headache, swelling and pain, which does not last for a long time.

The white-tailed spider

White-tailed spiders (Lampona sp.) can be recognised by their cylindrical body shape and a white or grey spot on the end of their abdomen. They are found in eastern and most southern areas of Australia and New Zealand.

These spiders are active hunters, preying on other types of spiders and insects. They may transiently roam inside houses, especially in warmer weather, where they may be found in bedding or clothing that has been left on the floor.

One study of over 70 spider bite cases in which white-tailed spiders were identified showed patients experienced only a mild localised reaction, such as swelling, local pain or headache. To date clinical research has not been able to associate tissue loss with the venom of these spider bites.

image White-tailed spiders can be recognised by their cylindrical body shape. Robert Raven, Author provided

Flesh-eating bacteria

The man at the centre of the recent story linking amputations to a white-tail spider bite was said to have a “flesh eating” infection. But there is a very low probability of an association between spiders and necrotisisng fasciitis (commonly known as flesh-eating disease).

Of course, any injury that causes a break in our skin leaves the capacity for bacteria to enter our body. Therefore be sure to keep an injury area clean. Questions have been raised as to the possibility of a spider introducing infections, but again, despite it being theoretically possible, it is unlikely.

Contributing factors to infection are if people have conditions such as diabetes or take medications, such as steroids like prednisolone, that lessen the body’s ability to fight infection.

How to prevent spider bite

  • Leave them alone
  • wear gloves if gardening
  • humanely remove spiders from your home and limit hiding spaces where possible inside the home
  • knock out shoes before putting them on; these are nice quiet homes for spiders.

For first aid after a spider bite, please see the Australian guidelines. Many bites don’t result in envenoming and death is very rare, so it is important to remain calm. But seek medical attention if there are concerning symptoms such as those described above: difficulty breathing, increased heartbeat and pain lasting longer than an hour.

Authors: Ronelle Welton, Scientist AVRU, University of Melbourne

Read more http://theconversation.com/the-truth-about-spider-bites-in-australia-theyre-unlikely-to-eat-your-flesh-75836

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