Autumn is the time when people typically notice spiders in their houses and there is usually an increase in the number of media stories suggesting that spiders – particularly the false widow spider – may be harmful. The false widow, Steatoda nobilis, is the UK’s most venomous spider and in one recent sad story in Hampshire it was reported that its bite contributed to the first death caused by the spider. But the evidence would suggest otherwise.
The false widow, which gets so much attention, can certainly give a “nip”, so this species can be a nuisance. But perhaps rebranding it as “slightly tetchy spider that is trying to do you a favour by eating pest insects in your house but will give you a nip that could be like a bee sting if you poke it (well wouldn’t you be a bit cross if you were in its place?)” might not have the same ring as “killer spider in your house”.
Reports of venomous spiders are serious and require a thorough look at the evidence. As an evolutionary biologist who studies spiders at the University of Nottingham, I have done just that, and there are two main pieces of evidence that the false widow is not the primary cause of the death in Hampshire.
The first of these is that the symptoms described do not fit the profile of this kind of spider’s venom. Spiders of the black widow group produce neurotoxins that act on the nervous system.
These toxins have been very well studied in the “true” widow spiders found in places like Australia and so we know what to expect they will do once they enter the human body: they cause symptoms such as muscle pain, vomiting and sweating.
The symptoms in one reliable report of a woman bitten by a false widow spider in Worthing in the 1990s were exactly as predicted: the bite was painful and the person reported feeling systemically unwell for a while. What these spiders are categorically not expected to produce are venoms that cause necrotising bites (which a small number of spiders in other parts of the world can make). And no spider found in the UK produces these kinds of venoms, so we are quite safe from these.
We do know, however, that our skin is an amazing barrier to a vast array of bacteria that surround us. Any puncture wound (be it from a household object like a sewing needle, or a carpentry nail, or potentially a spider’s bite) can allow bacteria in and from this there is the potential for bacterial poisoning to occur.
From the descriptions given in the media of the Hampshire case it seems much more likely that a wound became infected. There was a significant time period of a month after the proposed spider bite before the problems became serious. This in itself suggests that a neurotoxin was not the primary cause of the ongoing problem, or perhaps an allergic reaction. In another case reported in September, two reported fang marks appeared to confirm a spider bite but the reaction appeared consistent with bacterial infection.
The second thing that suggests that we should not worry about false widow spiders in our homes or elsewhere is that this spider isn’t aggressive and very rarely bites – and if it does so it even more rarely causes a problem. It originally came to the UK from the Canary Islands but we certainly don’t hear that people there regard the spider as a danger, or of holiday makers going to Tenerife and being bitten. I could not find a single report of a false widow spider bite requiring medical attention in the Canary Islands and yet this really would have made the news headlines.
Incidentally, the spider came to the UK more than 100 years ago and in all that time seems to have got as far as the Midlands – and a few other places in the UK – which doesn’t exactly appear to be a rampage.
Good things about spiders
So why are people so scared of spiders? One of my interests is in science outreach (including work with the Open Air Laboratories project, a hands-on citizen science initiative that gets people closer to nature) and it is interesting that children in primary schools – and even in nursery – are not usually scared of spiders. I suspect much of our fear as adults is a learned response based on seeing other people’s responses.
I try to dispel myths about what spiders can and can’t do and focus on the really amazing things that spiders do for us. I tell people how many pests money spiders eat (for free) which means we can avoid using pesticides in farmers’ fields. I tell them that house spider silk is antibacterial (my lab showed this to be true, so don’t worry too much about hoovering up those cobwebs).
I handle spiders in front of people and I tell them that spiders can fly through the air using silk as a sail (a behaviour called ballooning). Some individual spiders potentially travel many kilometres a day and might even cross continents (over time). This an incredibly risky thing to do because spiders cannot control where they land.
So here we are in 2014 and same as last year, people notice spiders in the autumn as it gets colder and more are seen indoors. I’ve already “rescued” several house spiders at work that have been tiptoeing around and alarming my colleagues.
Spiders in general are endlessly fascinating creatures to study and understand, and when it comes to the false widow in particular, should we be worried about them in our homes? The answer is an unequivocal “no”.