Spider attack or a web of lies?

One of the more common types of public enquiry I get as a natural history curator is about spiders. Every year in September people start reporting large spiders that they don’t recognise and which therefore *must* be invasive species or tropical escapees from packets of bananas. Every year I either reassure (or disappoint) those people by explaining that the spider they have discovered is a common species in its fully-grown adult stage, sometimes looking a bit on the bloated side because it’s full of eggs.

Araneus_diadematus_comparison

Garden Spider (Araneus diadematus) full of eggs. Inset: comparison against non-gravid Garden Spider abdomen – note the characteristic cross pattern.

This year has been a bit more active on the spider enquiry front, because there has been a lot of scaremongering about spiders in the tabloid press. Beyond the usual September influx of sightings when adult male spiders become more active as they seek females to mate with, there has also been an increase in the number of requests for identification throughout the year, with people unnecessarily concerned about the Noble False Widow (Steatoda nobilis) spreading steadily northward as the global climate warms.

Male Giant House Spider (Eratigena atrica) on the lookout for females. Inset: note the 'boxing glove' pedipalps that show this is a male

Male Giant House Spider (Eratigena atrica) on the lookout for females. Inset: note the ‘boxing glove’ shaped pedipalps that show that this is a male

With all this frenetic arachnological activity I thought it might be time to lay to rest some common misconceptions about spider bites and offer a reality check to counter some of the over-hyped reports of injuries blamed on spiders.

Spider bites

Spiders in Britain are pretty harmless critters. So far there have not been any reported deaths in the UK from spider bites ever. You are literally more likely to be killed by being struck by lightning.

This is partly because spiders very rarely bite people, despite what you might be told by the press. The UK is full of things that do bite however, such as mosquitoes, midges, horseflies, ticks, bed bugs and fleas. All of these unpleasant beasties have a reason for biting – they are after your blood. Spiders are not. They will generally only bite when they feel very threatened.

Another reason why spiders in the UK are not life-threatening is simply that their venom doesn’t pack enough punch. The most venomous spider living in the UK is the Noble False Widow, which can give a painful bite, similar in intensity to the sting of the Common Wasp (Vespula vulgaris).

NobleFalseWidow

Noble False Widow spider – a little visitor in my kitchen

Keep in mind that a Common Wasp is far more likely to sting you than a Noble False Widow is to bite you, since the spiders are not aggressive – they largely keep to themselves and they don’t try to mug you for whatever sugary food or drink you have available.

A few other spiders in the UK can also bite, sometimes painfully, but again their venom is meant for subduing small invertebrates rather than humans, so although you may get some pain and perhaps swelling some time after being bitten, that may persist for a few days, it shouldn’t cause you any serious problems unless it gets infected.

Spider bite or MRSA?

Now this is where it gets interesting. Cellulitis caused by bacteria like Staphylococcus aureus (or ‘staph’ for short) can commonly be mistaken for spider bites. Any bites, stings, scrapes, cuts or even hair follicles in the skin can open the underlying tissue to infection, leading to necrosis of the skin, similar to that caused by the bite of certain spider species – in particular the Brown Recluse (Loxosceles reclusa), which it’s worth noting does not occur in the UK.

Cellulitis - not a spider bite! Image by James Heilman, MD

Cellulitis – not a spider bite. Image by James Heilman, MD

In areas of the USA where the Brown Recluse is also not present, it still gets blamed for a large number of injuries that are actually caused by staph bacteria that are resistant to Methicillin antibiotics (this is the strain of bacterium more commonly known as MRSA). In one study assessing the possibility that MRSA had become established in a prison community, half of the study group incorrectly assumed that the symptoms of their MRSA infection were symptoms of having been bitten by a spider.

In fact, it seems that spiders regularly get blamed for injuries that they don’t cause. One American study reported 216 medical diagnoses of Recluse bites in Western states in 41 months, despite the fact that the spiders don’t naturally occur in those areas. In fact there had only ever been 35 confirmed sightings of Recluse spiders in the regions studied, which really doesn’t add up: how can non-existent spiders be biting people?

Why blame spiders?

It seems that there are a few factors at play here, not least irrational arachnophobia fuelled by irresponsible reporting in the press. People are told about ‘deadly’ spiders and then when they get an infection they assume that it’s actually a reaction to a spider bite. They then tell the media they’ve been bitten by a spider and the vicious circle is complete.

People also assume that a bite has been caused by a spider because they have seen a spider nearby. However, that spider is probably an innocent bystander that’s more interested in eating the bloodsucking pest that actually caused the bite – assuming that it’s a bite at all and not cellulitis caused by something else.

Cellar Spider (Pholcus phalangioides) feeding on a different spider species

A Cellar Spider (Pholcus phalangioides) intent on feeding on a another spider species and not remotely interested in biting humans

Finally, the effects of spider venoms are often very poorly understood, because they are so frequently conflated with a variety of other dermatological problems and the rarity of confirmed bites means that little research has ever been carried out. That means medical staff are operating from a poor information base and may rely on poor information when making a diagnosis. The danger here is that significant medical issues (such as the spread of MRSA) may be overlooked because spiders are being unfairly blamed.

So if you read a case in the media about some horrible ‘spider bite’ it’s sensible to remain a bit sceptical. If the spider wasn’t seen actually doing the biting, the chances are the injury wasn’t actually caused by a spider at all. More likely it’s an infected wound, maybe following a bite or sting from something else with a taste for human blood or the sweet things we eat ourselves.

Oddjects No.1

I’ve been running my mystery object for over three years now and I’ve decided to add another kind of post in order to share some of the odd and interesting objects that I come across as I work in the collections of the Horniman Museum.

To share these specimens I’ve chosen the name ‘Oddjects’ as a portmanteau of ‘Odd’ and ‘Objects’. Here’s the first:

Oddject1

This happens to be a Wolffish (Anarhichas sp.) specimen that was a mystery object back in 2010, but here I just want to use the specimen to capture the imagination and spark discussion rather than provide much in-depth interpretation.

What does this make you think of?

I hope you enjoy the Oddjects I plan to share – if you do I would heartily recommend also checking out the Twitter and Tumblr feeds for the Horniman’s collections review projects as they also share some great objects.

Friday mystery object #168 answer

On Friday I gave you this specimen to identify:

As I suspected, the distinctive shape of the skull makes this specimen easily recognisable as an owl (family Strigiformes). However, there are a couple of hundred species of owl, so there were plenty of possibilities to make a more specific identification.

This specimen has quite a distinctive slope to the forehead in profile view and a very clear groove down the midline of the cranium, which combined with the length of around 58mm narrowed down the likely suspects considerably.

Jake was the first to suggest the species I think it’s most likely to be, with palaeosam suggesting the other possible option and RH cautiously suggesting both. This skull belongs to an owl in the genus  Continue reading

Friday mystery object #166 answer

On Friday I gave you this great skull from the Grant Museum of Zoology to identify:

A big list of you (Mieke RothJakemcarnall, Anthony wilkes, 23thorns, Cam Weir, henstridgesj, Rhea, leigh and Robin) managed to work out what this specimen was from and there were some really interesting explanations about how you came to your conclusions in response to Steven D. Garber’s comment:

Now, I’d like it even more if people explained why this skull looks the way it does.

This is a really interesting thing to consider, as it underlies the process of recognition and identification. As a biologist I might start by saying that the lacrimal foramina is on the edge of the orbit (as henstridgesj pointed out) which is indicative of a marsupial and that the dentition is indicative of a carnivorous mammal that isn’t a member of the placental Carnivora as it lacks carnassials, plus the dental formula appears to be ‘primitive’ from the photo ?.1.3.4/?.1.2.4 which narrows down the possibilities to just a few marsupial carnivores, and given the scale of the skull there is just one that fits the bill.

However, if I’m honest I’d say that the overall shape and robust structure of this specimen is very similar to specimens I’ve seen before belonging to the  Continue reading

Friday mystery object #165 answer

On Friday I gave you this object from the Horniman collections to identify:

It’s fairly obvious that it’s a claw, but the question is what is it a claw from?

This claw was originally identified as being from a big cat of some kind, but it isn’t the right shape. A big cat claw has a thicker body with an acute sharp point – as with this Tiger claw:

Although different from the Tiger claw, the mystery claw has several similarities – mostly the fact that it’s laterally flattened. This suggests it’s from a mammal since birds have more rounded talons, as mentioned by henstridgesj. The mystery claw has a strong and long curve, that looks like an adaptation for climbing. The large size narrows it down to just a few possibilities and the little bump in the middle of the inside edge is quite distinctive.

There is a handy picture with a variety of claws that Carlos G found, which proved to be useful:

Robin and Carlos G managed to get it down to the right family and palaeosam and henstridgesj identified it to species. It’s the claw of an  Continue reading

Friday mystery object #164 answer

On Friday I gave you this object to identify:

It was a bit of a tricky one, since a few vertebrae aren’t a huge amount to go on. However, the large size helps narrow it down, as do the distinctively long neural spines.

As Ric Morris and henstridgesj spotted, the vertebrae are very compressed, not providing much scope for movement, suggesting an animal that relies on a rigid backbone for support and transferring large forces. This is not something you see in whales (at least not after the cervical and first few thoracic vertebrae), since water supports their weight and they maintain some flexibility in their spine for changing their orientation in the water when swimming. That leaves us with very few terrestrial mammals big enough to have vertebrae of this size – particularly considering that these vertebrae are from a juvenile animal.

The neural spines are long, but not laterally flattened. This suggests that they are not from a large Buffalo, Hippopotamus or Rhinoceros, since all of these animals have their neural spines orientated as a dorsal blade. The only animal of the right size that has dorso-ventrally flattened neural spines in the mid-thoracic region (that I’m aware of) is the  Continue reading