September opened with unsettled but unseasonably weather in much of the UK, with eastern and northern areas seeing the lion's share of the warmth and sunshine while the south and west were hit by heavy thundery showers. We saw a brief pulse of cold air during the second half of the month, resulting in some cooler nights, before temperatures climbed back up. The month ended on a stormy and chilly note.
News and discoveries
Beneficial bats. With Halloween on the horizon, bats are a seasonally topical species. Courtesy of the frequency with which they're linked with evil and the paranormal in human culture, bats have a bad reputation as animals to fear. The reality couldn't be more different. We know that bats are important pollinators of some tropical plants, and they also provide a natural pest control service. Indeed, in North America, bat populations have collapsed since 2006 with the arrival of a white-nose fungus. A recent study published in Science found that this collapse prompted farmers to apply more pesticides to their crops, which in turn raised the infant mortality rate in bat communities by eight percent; this may not sound like much, but it precipitated just over 1,330 infant deaths between 2004 and 2017. The additional pesticides needed to replace the bats cost an additional $27 billion over the same period.
Pollution emotion. How sensitive we are to climate hazards determines our vulnerability to climate change. A new approach by psychologists at Stanford University, published in PLoS One in August, sets out a framework for identifying how a person's underlying emotive state (known as their “affective state”) changes according to air quality. The data, based on following 150 Americans for just over a year, suggest that our mood is impacted by air pollution, and some people are hit harder (i.e., more prone to experience anxiety and depression) than others. Given that the World Health Authority estimate that 90% of the world's population breathe air that does not meet its standards for liveable air quality, understanding the influence of air pollution on human mental health is important.
Tuberculosis tack. The UK government has announced it intends to start work immediately to end the culling of badgers in England in response to the bovine TB epidemic, suggesting it may cease by the end of this Parliament, in 2029. At the same time, it set a goal of eradicating the disease in England by 2038 with a plan that now includes an up-to-date survey of the remaining badger population and a widespread badger vaccination programme. The current TB strategy, which involves shooting badgers to reduce disease prevalence in the wildlife reservoir and slaughtering cattle herds infected with TB, currently costs taxpayers more than £100 million every year. A new “Badger Vaccinator Field Force” is due to be created to increase the number of badgers vaccinated, while the impact of the vaccinations will be closely assessed to establish efficacy and the prevalence of the disease in the population. Reassuringly, there is also increased funding for research into a TB vaccine for cattle. The National Farmers' Union continue to question the feasibility of vaccinating badgers and cattle, pointing to research supporting culling as an effective approach, but given that this is ultimately a bovine disease and most transmission is between cows it's difficult to see a long-term solution that does not revolve around eliminating spread within the primary host species.
Seasonal highlight – The truth about spiders
Spiders hold an interesting place in our psyche. A few hardy souls love them (I'm one such person), a few tolerate them, but many more are terrified of them. Arachnophobia is one of the most common phobias experienced today, with about half of all women and one-fifth of men suffering from the condition. Symptoms range from a mild discomfort in their presence to a paralysing fear. Arachnophobia is an interesting phobia because it appears to override the ability of affected people to correctly estimate the size and speed of spiders. In an interesting paper published in 2012, researchers at Ohio State University reported that the greater someone's phobia of spiders, the more likely they were to significantly overestimate the size of a spider and, when shown a video of a spider moving towards them, the less able they were to correctly estimate when the spider would reach them (always underestimating the time).
All of this makes evolutionary sense (if you're scared of something, swerving to avoid it too soon rather than too late is almost certainly beneficial to you), but it can be debilitating for the afflicted party. Behavioural therapy has managed to cure some of their arachnophobia, but it can be a protracted process, taking upwards of six months. Alternatively, you can gradually desensitise yourself to spiders by simple things such as saying your fears out loud, looking at photos, or watching someone else handle a spider. Getting over a phobia takes time, but it is possible with the right approach and support, so if you attempt it, please be patient with yourself. As a prelude to improving our understanding of spiders at a time when we're most likely to find them in our houses, here's a quickfire Q&A on these amazing arachnids.
Are some autumn's spiders bigger than other autumn's?
This is something I see on social media a lot. It's hard to say with any certainty whether one year's crop of spiders is bigger than another, though, because there are no data sets comparing spider body size year on year. That said, some scientists think that a mild winter and warm, largely dry summer and start to the autumn provides a bumper crop of invertebrate prey. With more food on offer, spiders may be able to grow to their upper size limits.
Are there more spiders around some autumns than others?
The answer seems to be yes. As our climate changes to one of hotter summers and milder winters, this doesn't just provide more food, it also potentially means that fewer spiders perish during the winter and more spiderlings survive to adulthood. It should be noted, however, that as already mentioned, there is no national spider census conducted to monitor spider numbers in Britain so it is very difficult to make statements about how their numbers vary year on year. A survey by the charity BugLife published in 2009 suggested that every domestic property (i.e., house and garden) in Britain has, on average, 30 spiders, which adds up to some 750 million arachnids. Given that we had, I would estimate, well in excess of 100 wolf spiders in our garden alone last summer, I suspect this may be a significant underestimate.
What types of spiders are likely to be coming into my house?
My news Facebook newsfeed has been brimming with spiders over the past few weeks and the photos are almost invariably of the same three or four species because, despite Britain being home to somewhere in the region of 700 different spider species, few find comfort in our homes. In that which follows I will use the most often used common names for the species, but the use of vernacular naming with spiders is something of a minefield because there is a huge tendency for different people to call different spiders by different names. I appreciate that most people don't care, but for clarity I will also include the scientific names.
The main spider people see running across the carpet or loitering on walls/ceilings is the aptly named house spider. House spiders aren't a single species, but instead a group of spiders placed within the Tegenaria and Eratigena. Most of the spiders in Eratigena were moved there from Tegenaria (which translates roughly to 'carpet weaver' and is a clue to the type of webs the females create) in 2013; Eratigena is an anagram of Tegenaria. There are just over 100 species currently known from these genera, several that are found in Britain, although normally only three are commonly found in houses and these light brown spiders all have fairly small bodies and long legs: the common house spider (Tegenaria domestica), western house spider (Eratigena saeva), and the giant house spider (Eratigena duellica), which are almost indistinguishable without a close-up inspection. The cardinal spider is also a member of this genus (Tegenaria parietina), indeed the largest Tegenaria species in the UK, but this is uncommon and found largely in the south-east of England.
Another species commonly found in houses, particularly bathrooms, is the cellar spider (Pholcus phalangoides), also sometimes called the Daddy-longlegs spider (not to be confused with craneflies). These spindly spiders have small heads and small, almost rectangular abdomens (the size of which swells according to how well fed they are) and very long, thin legs. Cellar spiders tend to hang out in the corner of ceilings and, if you approach too close, will vibrate in their webs in the hope that you can't see them. If you're arachnophobic, these are good to have around because they'll eat most other spider species, even much larger house spiders.
Increasingly here in the UK, false widow spiders are being found in houses. As with house spiders, the name false widow actually refers to any of several species in the genus Steatoda (meaning 'rotund'). In the UK we have six species, only two of which are found with any regularity in houses: Steatoda nobilis and Steatoda grossa. A third species, Steatoda bipunctata, also known as the rabbit hutch spider, tends to be found in outbuilding such as animal hutches and sheds. False widows appear to have increased their range north in recent years, but their distribution is still very patchy with most sightings from the south coast and south-east England. As far as I know, there are no records for northern England or Scotland.
There are a couple of tiny, less than half a centimetre long, spiders that are sometimes also found in (particularly old) houses: the stunningly spotted spitting spider (Scytodes thoracica), and any of a handful of jumping spider species, including the attractive black and white striped zebra jumping spider (Salticus scenicus).
There are other spider species that live on the outside of our houses, including the large black tube web spider. Again, this actually refers to any one of three species of the genus Segestria, but the largest species and the one that tends to make the tabloids is Segestria florentina, which is currently restricted to southern Britain. These are large black spiders that live in holes in walls, and you tend only to see their front legs poking out. Lace web spiders of the genus Amaurobius (of which there are three species) are sometimes found in cocoon webs in the corner of windows and are often misidentified as False widows owing to a broadly similar abdomen pattern. Finally, the fat, patterned spiders most of us see in our gardens sitting in the middle of their webs is the aptly named European garden spider (Araneus diadematus). None of these species tend to venture into houses of their own volition and, where they are found, they tend to have been carried in on clothing or other objects.
Why do spiders suddenly appear inside in autumn?
September and October is the breeding season for most of our common spider species so, in most cases, the spiders that we find in our houses at this time of year are male house spiders searching for females. The females live in lofts, behind skirting boards, in window frames, etc., all year round and the wandering males come inside looking for them during the autumn. It is currently thought that the males follow scent trails when looking for females and will often use the same routes each day in their search; this explains why, if you don't squash them, you often find a spider in about the same spot each night.
Some spider species have just evolved to live in human houses, where they relish the warmth, and a spider living in your bathroom or conservatory will remain active throughout most of the year, while those in the garden may go into a torpid state if the weather gets cold. There are also far fewer potential predators in a spider-friendly house; all they need worry about are other spiders!
Will the spider die if I put it outside?
Probably not, although it may depend on the species. In his 2008 book, Spiders: The Ultimate Predators, Stephen Dalton notes that the cellar spider (Pholcus phalangioides) is a lover of warmth and requires temperatures of at least 10C (50F) to survive, although I have not seen this quoted anywhere else and those in my un-heated shed seem to make it through even snowy winters. It's a commonly held misconception that spiders die off when the weather gets cold but, although some invariably do, many overwinter in a torpid state (with legs curled under their bodies to reduce their surface area and thus slow down heat loss) in leaf litter or under logs and bark.
Obviously, there is a greater chance that, if you put the spider outside, it will get eaten by a predator. It is also quite likely that it will simply find its way back in while you're not looking.
Are spiders dangerous?
Spiders are small predators; they catch and consume other animals. By virtue of their size, however, most spiders lack chelicerae (jaws) large or powerful enough to puncture human skin. Furthermore, spiders tend to keep themselves to themselves and bites occur either accidentally (when a spider has become caught/trapped in clothing, for example) or from deliberate provocation. I have observed and photographed many spider species, including false widows, from close range and have never felt that I was in danger of being bitten. If I evict a spider from the house, I take sensible precautions and put them into a cup/glass rather than handling them, even if I know the species to be harmless. A false widow living in a web in your bathroom, or a house spider on your ceiling, means you no harm and, if left alone, poses no threat.
What should I do if I've been bitten by a spider?
Keep calm. Many of the symptoms people report from spider bites are actually symptoms of shock. Typically, being bitten by a spider is no worse than a wasp or bee sting, but some people are allergic to spider venom and can experience an anaphylactic response. Generally, a spider bite will manifest as a small lump that is reddened and swollen and may have two small, but discernible, puncture marks. So, remain calm and treat the wound as you would any insect bite or sting; clean the bite and apply antiseptic cream/liquid. The horror stories you may have read in the tabloids about spider bites leading to amputations are vastly exaggerated; it's exceptionally rare and occurs when the wound becomes infected with bacteria from the victim's skin or environment. If you're concerned about the bite, contact your GP. If you experience symptoms of anaphylaxis—i.e., red skin rash, swollen face (particularly lips or eyes) or hands/feet, wheezing or other difficulty breathing, abdominal pain, nausea, etc.—seek medical attention as a matter of urgency.
Green fanged spiders in the UK! Really?
Sort of! The ominous-sounding 'green-fanged spider' of Daily Mail fame is actually the tube web spider Segestria florentina. These are the large black beasties that you see in holes in your house wall with their front legs sticking out while they wait for something to trigger one of the spoke-like trip-lines of their web. The chelicerae of females reflect faintly green under torch light. These spiders are among the few that can puncture human skin, but they are rarely found indoors. This species has been in the UK since at least 1845, although it appears to have expanded its range considerably since the early 1990s.
Are there really False Black widows in the UK?
The first thing to address here is the use of the term black in the vernacular name for this spider, as it immediately conjures up images of the notorious black widow spider of the tropics. It is very important to stress that, despite sharing a broadly similar body plan and web design, false widows are not a 'type' of black widow spider; they are not even part of the same family. Black widow venom is highly potent and can kill humans, while the venom of the false widow is substantially milder and, unless you have a specific allergic reaction to it, is no more problematic than a bee or wasp sting. The false widow species most likely to be encountered in homes and out-buildings is Steatoda nobilis, and this species has been in the UK since the early 1870s; its range has extended since the mid-1980s.
What purpose do spiders serve?
Spiders are predators of animals, so they play an important role in maintaining species balance within an ecosystem. In your house, spiders will happily eat a whole range of creepy crawlies that you may consider pests, including flies, silverfish, earwigs, moths, as well as other spiders. In your garden, spiders are also prey for several species, including many birds.
Why do spiders sometimes stop half-way across the floor and watch me for several minutes before carrying on?
Don't worry, it's not sizing up your weakness in preparation for an attack. Quite simply they run out of steam. Spiders don't have lungs like ours. Instead, most species have a pair of flattened, disc-like structures in their abdomen called book lungs. These are highly vascularised structures (i.e., have a high density of blood vessels) from which radiates a network of tubes, called tracheae (pronounced track-e-a) that deliver oxygen and remove carbon dioxide. This method of gaseous exchange is good at conserving water (we lose a lot of water with each breath), but much less efficient at delivering and extracting oxygen from the air than mammalian lungs. As it happens, it's actually the impact that this lack of oxygen has on the rate that they can perform certain biochemical reactions (including neutralising lactic acid and generating the phosphate needed by their muscles) that is the key here; but that's a bit beyond the scope of this Q&A. Ultimately, spiders lack stamina and need to stop and rest periodically after exerting themselves. Indeed, most spiders can only run for, on average, 20 seconds before needing to stop and recover.
For a round-up of Britain's seasonal wildlife highlights for mid-autumn, check out my Wildlife Watching - October blog. To learn more about the pannage season, which is in full swing here in the New Forest this month, check out Pigging Out on the Forest.