Monday, December 6, 2010

Spider Bites

New Zealand has only three spiders that have bites that can cause us concern for our health; the common White-tail spider, the rare native Katipo spider and its cousing the Australian Redback. The Redback is also rare but becoming more common in New Zealand according to AgResearch scientists. The Redback and Katipo have powerful venom that can be very painful and on rare occasions Redback bites can be life threatening. However, the rapid administration of anti-venom has meant that no one has died from a Redback bite for more than 50 years in its native Australia.

Adult female White-tail Spider
There is controversy over the risks posed by White-tail spiders. There is much hearsay evidence that the bite of a White-tail can cause ulceration and necrosis, but published studies of confirmed White-tail bites have not shown any link. It is accepted that their bite is painful and can cause localised swelling and itchiness.

White-tail spiders are hunting spiders. They hunt other spiders. Their normal habitat is among leaf litter, but they find our homes and buildings suitable for them to live. They often find an abundance of other spiders to feed on and dark dry areas like roof voids to build their nests. The nest of a White-tail is a tangled mass of silk where they lay their eggs.

Insect and spider bites and stings, whether from wasps, blood sucking insects, biting flies or spiders involve puncturing the skin and therefore some risk of infection. The infection can be directly from bacteria on the insect or spider mouthparts or from subsequent invasion of disease organisms at the bite site. Because bites and stings often become itchy they often get scratched. Scratching can open up bites to infections that could be serious. Perhaps such infections are the source of the ulceration and necrosis reported following White-tail bites. Avoid scratching bites. Application of anti histamines or topical steroids can reduce itchiness and swelling.

Spider bites can sometimes (but not often) be differentiated from bites of insects such as fleas or bed bugs. Spider bites involving venom usually cause pain prior to inflammation. Spiders use two fangs to bite and inject their venom so it is sometimes possible to identify two puncture wounds very close together.

Spiders are a beneficial part of the natural ecosystem, but many people have a fear of spiders and as discussed, some pose a risk to our health. A simple spider proofing treatment of a house can be carried out that will keep spiders outside and leave our homes spider free. Residual insecticides such as NO Spiders or NO Bugs Super can be purchased from good hardware stores. Spray around the exterior of a building where spider webbing is seen and where spiders could gain entry. Inside, spray the bottom and tops of walls, behind furniture and appliances and in voids such as roof spaces. NO Bugs Bug bombs or NO Bugs Borafume fumigators can be useful in hard to access areas.


A whitetail spider walks into a bar.
The bartender asks "What's your poison?"

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