Thank Christ someone chimed in with the facts eventually in this thread ! In Australia the media has ‘beat up’ the myth that white-tail bites cause necrotising arachnidism. Nice work Lara, you rock !
The study published last year that Lara alludes to by Isbister and Gray is the most powerful and convincing evidence to date that white-tails don’t cause necrotising arachnidism. They only included patients that had captured the spider that bit them on the spot, and they had all spiders identified ‘in the flesh’ by experts. Impressively, and relevant to Paul’s post (above) suggesting that there could be an odd species distribution accounting for anecdotal reports of white-tail induced ulceration, they went as far as identifying all ‘white-tips’ (Different Lampona genus spiders) down to the species level.
130 certified white-tail bites, zero necrotic lesions. Relevant to the above post from “ax”, they also confirmed zero infections.
http://www.ncbi.nlm.nih.gov/entrez/q..._uids=12914510

There is another interesting study relevant to Isbister and Gray’s final conclusion (see Lara’s post, directly above), particularly their assertion that “Previously we have shown that there were no necrotic lesions when all spider types in Australia were analysed. These data suggest that spiders are an extremely uncommon cause of necrotic or cytotoxic lesions, and should be considered only at the end of a long list of other differential diagnoses”

This seems to amount to a tactfully phrased (but wise) suggestion that when patients present with necrotic lesions that they think were caused by a spider bite, they are most likely to be wrong (and inadvertently misleading the physician to their own detriment).

One group has investigated this specific question scientifically, and just published their results this year. Probably because white-tails do not actually cause necrotic lesions, the sample size (the number of people that actually presented with existing lesions that the patients themselves believed were caused by white-tails) was small, 11. So the study is nowhere near as powerful as Isbister and Gray’s. But like the venom study alluded to by ‘Rod’ above, it is completely concordant with their conclusions.
Physiologically verified alternative causes of ulceration ? All 11 patients. Their conclusion:
“In this series, all cases initially referred as WT spider bites or necrotic arachnidism were found to have alternative diagnoses with appropriate investigations. This demonstrates that spider bites are an unlikely cause of necrotic ulcers and that all ulcers should be properly investigated with bacterial, fungal and mycobacterial cultures and skin biopsy for histopathology”.
http://www.ncbi.nlm.nih.gov/entrez/q..._uids=14748912

So why does the myth persist. ? In my humble opinion it is the product of a combination of irresponsible media hype, and human psychology.
Applying principals of psychology, I think people would often feel embarrassed when they develop necrotic skin lesions, because they’re disfiguring and ugly. People are more comfortable believing that such ailments are due to external causes, that are clearly ‘not their fault’, rather than an internal deficiency or the like. I hope this suggestion doesn’t offend anyone.
Cheers, Owen Proudfoot