Once and for all: are white-tailed spiders dangerous or not?

Here in New Zealand we have precious few animals capable of inflicting grievous bodily harm, and jealously guard and cherish the few we have. The katipō spider, the redback spider and the white-tailed spider are our holy trinity of dangerous arachnids.  So it’s no wonder the debate over the white-tailed spider is such an emotional one.

Once every few years, the discussion reignites in some public forum, and it usually goes something like this: someone will post a scientific study saying the case for white-tail spider venom causing serious harm is misleading, and that white-tailed spiders are simply a popular scapegoat for any infected skin lesions. And then you scroll down to the comments section to see 150+ photographs of festering wounds that look straight out of custard week on The Great British Bake Off.

So what’s the answer? Are white tail spiders dangerous or not?

I asked Phil Sirvid, curator of Invertebrates of Te Papa and spider apologist, if white-tailed spiders have an undeserved reputation. “Very much so”, he said. 

He pointed me to an Australian study published in 2003 of 130 confirmed white-tailed spider bites, investigating the “incidence of necrotic lesions.” A necrotic lesion is when living tissue dies, usually due to infection or trauma, and has to be cut away. The result is so disgusting that Google has applied a “SafeSearch blurring” feature to the image results; the faint of heart may prefer to picture a chargrilled crème brulée.

While participants recorded pain in 100% of white-tailed bites and there is plenty of evidence of puncture wounds, redness, itchiness and occasional “wound weeping”, there is zero evidence of necrotic ulcers.  

130 participants, as Sirvid points out, is a pretty good sample size. “And this is a case where the study looked at spiders caught in the act of biting, so there’s no doubt they’d been bitten by a spider rather than a wound from something else. And the spider was properly identified by an expert. So that’s as good as you can hope for I think.” 

It seems as if this evidence is pretty conclusive. And yet when I threw the question out there on Instagram, I received a torrent of upsetting and horrible messages about festering genital wounds, golf-ball-sized lesions, and a bite between the toes that turned one friend’s foot white and smelled so badly of rotting flesh it made her doctor retch.

Tallying up the incidents, I counted:

• 1x person bitten in the balls
• 1x person bitten on the vulva
• 1x person bitten on the groin (during church)
• 1x child with cellulitis
• 1x chunk of leg surgically removed, after someone was bitten by a spider on a construction site, only to return to work a few days later and have the same thing happen AGAIN
• 3x bites in the thighs that left “swollen and black and weeping” wounds
• 3x large pus sacs
• 1x wound the size of a golf ball
• 1x wound the size of a tennis ball
• 2x scars like bullet wounds
• 3x spider-bite-based relationship breakups (potentially unrelated) 

And a number of other stories which are too painful and personal to glibly reproduce here. 

My favourite story came from Isaac Strati, who, after being bitten by white-tailed spiders three times, said: “The prevention my hippy parents decided to do was burn the spiders and leave the charred bodies in little plates as some sort of warning. I  think it worked?”

So what of all these people? Were they imagining their horrible white-tailed spider injuries?

“Never say never,” says Sirvid. “There may be a few people out there who will react differently to everyone else, just like there are with bee stings. But we don’t know that for sure. It seems more likely that in most cases, secondary infection of the wound after the fact is a bigger problem. And any wound can have that happen. I’ve got scars on my skin from one such incident.”

All of the respondents were people I know to be careful and intelligent, and claim to have responded to their bites promptly. It doesn’t seem fair to accuse these upstanding citizens of improper wound care. 

The good news is that we can, at least, blame Australia. The white-tailed spider is a native Australian species which hitched a lift over the ditch in the 1870s. There are two species of white-tailed spider living in New Zealand: Lampona murina, which lives in the North Island, and Lampona cylindrata, which lives in the South. 

“Just looking at them, you wouldn’t be able to tell them apart easily,” said Sirvid. “You actually need to get them under a microscope to see the differences.” Despite managing to find their way over from Australia, it seems as if white-tailed spiders haven’t been able to figure out the Cook Strait. “I’ve never yet seen one on the wrong island.”

I asked if it was possible that the two species of spiders have different kinds of venom, and that could account for people’s reactions to the bite. But as Sirvid says, “there’s no reason to suggest that either one is more nasty than the other.” 

On any white-tailed spider comment section, there’s always someone claiming that because white-tailed spiders are spider hunters, their bites may be nasty as a result of their diet. I ran this theory past Sirvid, who quickly debunked it.

“Even if they do kill other spiders, the whole way that spiders feed – basically flooding everything with digestive enzymes and – it’s not as though spiders can co-opt the venom of another species to inflict it on us. And even if that were true, the only ones we’d be worried about would be katipō and redback. So unless it was meeting those, which it isn’t… fundamentally the whole way spiders feed rules against it.” 

Sirvid points out that because white-tailed spiders have such a bad reputation, they are frequently blamed even if there is no evidence to suggest they were responsible for the wound in the first place. “When people have an experience like this, whether they saw a spider or not, there’s a ready explanation for it called the white-tail. I can’t blame people for leaping to that conclusion. But one thing to be aware of in stories that you read in the media is if the person never felt the alleged bite, it probably wasn’t [a white-tail] because if we go back to that study, the bite is pretty painful.” 

There’s probably something to be said for the frequency of the bites having a direct correlation to the kind of environment white-tailed spiders prefer. Because they are itinerant and prefer to live in or around houses, white-tails are much more likely to end up between your bedsheets than more reclusive arachnids. 

Does this mean we should stop giving white-tailed spiders the old boot heel? 

Asking a spider expert whether you should kill a particular species of spider feels a little rude, like asking a marine biologist if Jaws got what was coming to him. But Sirvid is diplomatic. “You know, I wouldn’t blame someone for doing that,” he said, while probably secretly blaming me. 

I asked Sirvid if he’s ever been bitten by a white-tailed spider. He said he hasn’t, but wouldn’t want to be, reiterating that although their reputation for causing necrotic ulcers appears to be unjustified, it doesn’t mean the bites are harmless. Their bite is painful 100% of the time and can lead to complications, so it’s an experience to be avoided. 

So if you wake up to a stinging foot and three dead white-tailed spiders in your bed, what should you do? “People should always look after spider bites as if they’re suspect wounds because the infection can still get in, particularly if you don’t clean the wound and don’t look after it. And if there’s any untoward symptoms at all, get medical advice.” 

I asked him if it’s worth capturing the culprit spider for identification, where possible. “Always. Whether you know what it is or not, catching the spider is a really good thing. Because then someone like me may get to see it and confirm exactly what it is, and whether it’s worth worrying about. And there are very few in this country that are worth worrying about. Unlike Australia.” 

At the end of my investigation, I feel even more conflicted than when I began. On the one hand, the scientific evidence is both robust and reassuring. The data from the study appears to be the best evidence you could hope for. I like “Spiderman” Phil Sirvid and trust his professional expertise.

And yet the overwhelming amount of horror stories I’ve heard as a result of this conversation have, if anything, made me even more cautious. While the white-tailed spider might be maligned in many respects, its bite is certainly nothing to sneeze at. The next time you see a white-tailed spider in your bedroom ceiling, it’s probably best to burn the house down, just to be on the safe side.