Week 37
It has been a sadder week than normal, as I have encountered several problems. Everything started with the grass snake[i] that was killed on a road outside my house. I hate animal death, as the body invariably looks sad and lonely. The dead grass snake was no exception. The reptile happens to be the country’s longest snake and is expert at many things, including feigning death when threatened (thanatosis). Certain other animals can do this as well, such as rabbits and ducks[ii]. Sadly, the grass snake was properly dead.
Mostly, grass snakes are well equipped to get out of trouble. When up against it the reptile can release a foul-smelling substance from its anal gland and can also strike, just like any other snake, but only with its head. A grass snake is no danger at all to humans[iii] and is protected in the UK under the Wildlife and Countryside Act, 1981. It is a Priority Species under the UK Post-2010 Biodiversity Framework, meaning that it cannot be deliberately killed, injured, or traded in any way[iv]. On a more positive note, to see a dead snake is regarded by some as symbolic and generally indicates good health, wealth, change, the solving of problems, and rebirth. It can also be a warning sign, or an indication that there is broken trust somewhere in one’s life[v]. I will have to wait and see what the dead grass snake may mean for me, but so far I just feel sad.
I turned my back on the snake and walked slowly through my land, checking all was behaving as it should. The moss in The Mossarium looked healthy and the dead hedge was clearly being well used by small animals, likely mice. I then started to inspect the many oak seedlings and saplings that were beginning to turn into trees. I have a lot of them, almost anywhere I look.
Every few years, some species of tree and shrub produce a bumper crop of fruits or nuts. The collective term for these fruits and nuts is 'mast', which gives rise to the phrase, a mast year[vi]. The term derives from the Old English mæst, meaning the nuts of forest trees that have accumulated on the ground, especially those used historically for fattening domestic pigs, and as a food resource for wildlife[vii].
Two very recognisable trees, the oak[viii] and beech[ix], fluctuate massively year on year with the number of acorns and beech nuts they produce. Warm spring temperatures, as we have had this year, can lead to impressive crops of acorns. It is now too early to say if this year will also be a mast year, as I have just begun to see acorns dropping, but only in ones and twos.
The theory behind a mast year is predator satiation[x]. That is, if an oak produces a huge number of acorns, there are too many for wildlife to munch, and at least some will grow into trees. Mast years should occur every 2-5 years[xi], but it is difficult to be certain. There was a mast year in 2020, and likely also in 2022. This year is anyone’s guess.
However, as I slowly patrolled my land, one oak sapling worried me, especially as only two weeks ago it was healthy. Now it was looking very unwell. I had been planning to transplant it to another location on my land, but now I was not so sure. At its base, its leaves were green and healthy but nearer to its tip, now two metres from the ground, the leaves were curled and wilting. They were also white, no longer green and shiny, and covered in what looked to be talcum powder. I swore under my breath, as I recognised the problem immediately. I was looking at oak powdery mildew, not a happy sight.
Powdery mildew, and there are different varieties, is a fungal disease of foliage and stems, but occasionally fruits and flowers. Many common edible and ornamental garden plants are affected such as apples, blackcurrants, and gooseberries, or marrows, cucumbers, and peas. Powdery mildew is a major pathogen of cereal crops, many ornamentals in the daisy family, as well as rhododendrons, azaleas, roses, and before my eyes, the English oak. Fortunately, if such a word can be applied to powdery mildew, a specific species of the fungus usually has a narrow host range comprising of just a few related plants. For example, the powdery mildew affecting peas is different to the one that attacks oaks.
Most growth of powdery mildew is found on a plant’s surface. The fungus sends feeding structures into the surface cells, reducing the vigour of the plant. Because of this surface growth, powdery mildew is more heavily influenced by the environment than other plant diseases. Choosing the right plant for the right place is one very good way of minimising the risk of powdery mildew.
The powdery mildew fungi produce microscopic airborne dispersal spores from the fungal growth on the plant’s surface. These have an unusually high water content, enabling them to infect under drier conditions than most other fungal pathogens. High humidity, but not free water, is favourable for spore production and infection, and plants growing in areas with poor air flow, thereby allowing the accumulation of humid and stagnant air, are likely to be attacked. For this reason, climbers and ramblers grown against walls and fences are often heavily infected. Powdery mildews either spend the winter as dormant infections on green vegetation, or on fallen leaves, with release of spores the following spring[xii].
There are multitudinous treatments available for powdery mildew. For example, baking soda, potassium bicarbonate, neem oil, commercial sulphur-containing fungicides, and even milk[xiii]. Milk can be astonishingly effective, although different mixtures of milk and water have been suggested. For my case of oak powdery mildew, I decided to try milk, and have used a 40% milk: 60% water mixture, as well as removing the affected leaves and pruning the sapling’s trunk. How milk works has been extensively researched but the results are still uncertain. One theory is that milk protein has an antiseptic effect when exposed to sunlight, which is why milk should be applied in bright sunshine. The treatment should be repeated every two weeks until conditions are no longer warm and humid[xiv]. Let us see what happens to my oak sapling.
Many decades ago, when I went to school, I recall my mother making certain that I had a regular supply of rosehip[xv]. Today, whenever I see a rosehip, I remember those days, so I have been watching the red rosehip fruits grow, and now slowly rot, right outside my kitchen window. Rosehip is part of the fruit that grows on the blossom of a wild rose called Rosa canina, which is found mostly in Europe and parts of Africa and Asia.
Rosehip is incredibly useful medicinally and is packed full of vitamins B, C, and E, as well as other antioxidants and minerals. It contains more vitamin C than even citrus fruits, in addition to a substance that fights inflammation. Animal studies have also shown it to lower blood sugar, cholesterol, and blood pressure, and even reverse obesity[xvi]. Rosehip promises a lot and achieves plenty, although not always everything claimed. In addition to its medicinal uses, rosehip is much sought by birds as food during the winter, especially when the ground is too frozen to hunt worms or snails, and when there are few insects about[xvii]. One thing is certain, I had best look after my rosehips.
It has been a good year for roses, although I now have a few that are targets for pests. Sawfly caterpillars have gone into overdrive and are munching my rose leaves as if at a sawfly feast. This is normal for sawfly caterpillars, which can strip a plant of all its foliage - almost overnight in some cases[xviii]. The common name for a sawfly comes from the saw-like appearance of the fly’s long ovipositor, protruding from the female’s rear end, which is used to burrow into plants to lay eggs. There are many different sawflies, with more than 8000 described species and over 800 genera[xix]. There is generally no need to combat sawflies, as plants can withstand attack without suffering. What is more, the use of chemicals can kill beneficial insects such as bees and butterflies, as well as sawflies.
There are several organic techniques that can be tried in some circumstances, otherwise it is reasonable to let Nature take her course. These techniques include:
Cultivation - the caterpillars of many sawflies overwinter in the soil under their host plant, so cultivating the ground beneath susceptible plants by clearing debris and lightly raking the soil, will expose the caterpillars to the frost, and to being eaten by birds and other predators.
Hand picking - pick off and discard rolled-up rose leaves to prevent the caterpillars maturing, although with large numbers of leaves, they are best left, or the rose will suffer.
Hand squashing - inspecting the undersides of susceptible leaves in spring and early summer can reveal clusters of eggs, while leaves may be scarred where eggs have been laid. Intervening early and squashing with finger and thumb can prevent a large infestation.
Encourage natural predators - it is better to encourage natural predators to control sawfly than to control them oneself. Look out for birds, wasps and even ground beetles feasting on sawfly caterpillars and let them get on with it[xx].
Yet what the sawfly caterpillar has shown me is the importance of caterpillars. For much of my life I have looked at caterpillars with wonder, on occasion with horror, as I simply have not understood them. There are many people who have a caterpillar phobia, which is a well-described condition[xxi], although I suspect much of this is thanks to poor knowledge.
Caterpillars are officially the larval stage of members of the order Lepidoptera, the insect order comprising butterflies and moths. As with most common names, the application of the word is arbitrary since the larvae of sawflies (suborder Symphyta) are commonly called caterpillars, too[xxii]. Caterpillars have an essential role in natural ecosystems, acting as pollinators both before and after they have metamorphosed, and as a food source for various predators[xxiii]. Caterpillars are a primary food source for several bird species, making the existence of a vibrant bird population possible[xxiv]. Through their own feeding habits, caterpillars greatly influence the structure and composition of plant communities.
Sawflies develop through four life stages - egg, larva (caterpillar), pupa, and adult. After hatching from an egg, larvae develop through several growth stages, then pupate and emerge as an adult[xxv]. Caterpillars also serve as sensitive indicators of the health and vitality of the ecosystems in the Lake District. Their presence, diversity, and abundance are often reliable markers of the ecological richness of an area[xxvi]. Fortunately, there are plenty of caterpillars on my land, not just those of the sawfly. In the context of renaturing, when it comes to caterpillars, the more the merrier. Community science projects like the Caterpillars Count project[xxvii] by the University of North Carolina engage people in monitoring caterpillar abundance and diversity, thereby contributing valuable data to understand the role of caterpillars in the restoration of an ecosystem.
Despite an extreme heatwave taking place in UK this week, there is still some dew formation. When that happens, my land comes alive with dozens of spider’s webs. Because the webs are now simple to see, it is easy to see why autumn may be regarded as spider season. This is not actually true, as spiders are active all year, but the moisture in the air associated with autumn, and the frequent dew, makes the webs more obvious.
Dew is the moisture that forms because of condensation. Condensation is the process a material undergoes as it changes from a gas to a liquid. Dew is the result of water changing from a vapour to a liquid. As temperatures drop, and objects cool down, so dew forms. If the object becomes cool enough, the air around the object will also cool. Colder air is less able to hold water vapour than warm air. This forces water vapour in the air around cooling objects to condense, and small water droplets form - dew. The temperature at which dew forms is called the dew point. Dew is most likely to form at night, as temperatures drop and objects cool. However, dew can form whenever a dew point is reached[xxviii], even by day.
With so many spiders evident, certainly their webs, it is not everyone’s best time of year. I am happy with spiders but many around me do not feel the same. An intense fear of spiders, arachnophobia, is a well-recognised condition, affecting up to 15% of the human population, and is more common in females than males. However, there is fear and there is phobia - the two are different. Fear is a natural emotion that protects people from harm when they face real and imminent danger. A phobia is an intense and irrational fear towards one or more things, or situations, the level of fear not matching the actual danger presented by the feared object or situation[xxix],[xxx].
Yet despite widespread emotions, with so many webs now evident, it is a shame not to take advantage of them, as a spider’s web can say much about the spider. There are seven types of web - orb, sheet, tangle, funnel, lace, radial and purse. I cannot cover them all here.
The classic two-dimensional web that looks like a bicycle wheel or dart board is the so-called orb web. The radial threads act as a scaffold while the circumferential threads are sticky and laid down as a spiral by the spider. Common spiders that fashion orb webs are the garden orb-weaver[xxxi], the wasp spider[xxxii], triangle spider[xxxiii], and the garden centre spider[xxxiv].
Sheet webs are what I am mostly seeing on my land. They are normally built by the largest family of spiders in the UK, the Linyphiidae, of which there are 280 species. The webs are densely woven, thin, horizontal sheets that look like silken hammocks decorating grass and low bushes. Insects fall onto the hammocks or are knocked down when they collide with a tangle of threads above the sheet[xxxv].
The reason there are so many webs for me to see at the moment is not only because the dew makes it easy. It is also because September is when male spiders are searching for a mate. It is also why one can see larger spiders at this time of year. This should all be over by the end of October[xxxvi] and arachnophobes can once more relax.
I am sometimes confused between a spider’s web and that of a spider mite. However, there is a difference. The spider mite generally lives on the undersides of leaves of plants, where it may spin protective silk webs, and can cause damage by puncturing the plant cells to feed. Spider mites, and there are about 1200 species of them, are known to feed on several hundred species of plants[xxxvii]. Hot, dry conditions are often associated with a population build-up of spider mites. They do know how to procreate. One female spider mite can lay up to 20 eggs per day and can live for 2 to 4 weeks, thereby laying hundreds of eggs. This accelerated reproductive rate allows spider mite populations to adapt quickly to resist pesticides. This means that chemical control methods can become less effective if the same pesticide is used over a prolonged period.
Most of the webs I can see on my land, on its trees, shrubs, and flowers are made by garden spiders, not spider mites. With careful observation it is easy to tell the difference.
Spider mites only web when the infestation is severe. They spin a fine and sticky web and, in most cases, it is possible to see the tiny spider mites in the web. The webs also tend to engulf the leaf, leaves, stems or branches instead of being on the top of the plant or layered.
Garden spiders make their webs on top of the plants, or possibly in between the branches, but do not usually wrap up the foliage with their web. Their goal is to capture other insects, which includes spider mites, so they want their webs in the open. By looking closely at the web, it is often possible to find a tiny spider waiting in ambush[xxxviii].
As I write, as I think about this, I sense that arachnophobes have a point.
***
Acknowledgement
Take it from me - none of this would be possible without the help of RSG Horticulture. Rufus, who runs it, has far more energy than me and is full of ideas and skills. Do contact him through https://www.rsghorticulture.com.
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References
[i] See week 26 entry. [ii] Maxwell K. Playing possum: 9 animals that play dead to survive. 3 June 2023. See https://a-z-animals.com/blog/playing-possum-9-animals-that-play-dead-to-survive/. Accessed 7 September 2023. [iii] Grass snake (Natrix helvetica). See https://www.wildlifetrusts.org/wildlife-explorer/reptiles/grass-snake. Accessed 7 September 2023. [iv] Young People’s Trust for the Environment. Grass snake (Natrix natrix). See https://ypte.org.uk/factsheets/grass-snake/protecting-the-grass-snake#section. Accessed 7 September 2023. [v] Chris. Dead Snake Symbolism & 7 Meanings (Health and Change). 19 September 2021. See https://symbolismandmetaphor.com/dead-snake-symbolism-meaning/#:~:text=The%20dead%20snake%20is%20a,can%20manifest%20from%20this%20symbol. Accessed 7 September 2023. [vi] Whittle L. What is a mast year? How and why it happens. 27 October 2020. See https://www.woodlandtrust.org.uk/blog/2020/10/what-is-a-mast-year/#:~:text=Every%20few%20years%2C%20some%20species,and%20beech%20nuts%20they%20produce. Accessed 7 September 2023. [vii] Wikipedia. Mast (botany). See https://en.wikipedia.org/wiki/Mast_(botany). Accessed 7 September 2023. [viii] See week 23 entry. [ix] See week 23 entry. [x] Bubber G. The mystery of the mast year. 12 November 2020. See https://www.treesforcities.org/stories/the-mystery-of-the-mast-year#:~:text=Mast%20years%20are%20a%20canny,is%20called%20%27predator%20satiation%27. Accessed 7 September 2023. [xi] The Botanical Journey. Oaks & Acorns: The Mystery of the Mast. 31 October 2022. See https://thebotanicaljourney.com/blogs/the-botanical-journey/oaks-acorns-and-the-mystery-of-the-mast. Accessed 7 September 2023. [xii] Royal Horticultural Society. Powdery mildews. See https://www.rhs.org.uk/disease/powdery-mildews. Accessed 7 September 2023. [xiii] Hagen L. How to get rid of powdery mildew. See https://www.gardendesign.com/how-to/powdery-mildew.html. Accessed 7 September 2023. [xiv] Iannotti M. How to Use Milk Spray to Control Powdery Mildew. 15 October 2021. See https://www.thespruce.com/how-to-use-milk-to-control-mildew-1402739. Accessed 7 September 2023. [xv] Wikipedia. Rose hip. See https://en.wikipedia.org/wiki/Rose_hip. Accessed 7 September 2023. [xvi] Miller K. Rosehip. See https://www.webmd.com/vitamins-and-supplements/rosehip-uses-and-risks#. Accessed 7 September 2023. [xvii] Rose Hips. See https://community.rspb.org.uk/wildlife/f/wildlife-questions/6546/rose-hips#:~:text=to%20answer%20your%20question%20rose,there%20are%20few%20insects%20about. Accessed 7 September 2023. [xviii] Notcutts. Sawflies. See https://www.notcutts.co.uk/garden-advice/problems-pests/sawflies/. Accessed 7 September 2023. [xix] Wikipedia. Sawfly. See https://en.wikipedia.org/wiki/Sawfly#:~:text=Like%20all%20other%20hymenopteran%20insects,fertilization%20to%20create%20viable%20eggs. Accessed 7 September 2023. [xx] Fisher S. How to get rid of sawfly. 19 January 2022. See https://www.gardenersworld.com/how-to/grow-plants/how-to-get-rid-of-sawfly/#. Accessed 7 September 2023. [xxi] Caterpillar phobia. See https://healthresearchfunding.org/caterpillar-phobia/. Accessed 7 September 2023. [xxii] Wikipedia. Caterpillar. The origins of the word "caterpillar" date from the early 16th century. They derive from Middle English catirpel, catirpeller, probably an alteration of Old North French catepelose: cate, cat (from Latin cattus) + pelose, hairy (from Latin pilōsus).See https://en.wikipedia.org/wiki/Caterpillar. Accessed 9 September 2023. [xxiii] Hossain Z, Gurr GM, Wratten SD, Krutmuang P. (Lepidopteran caterpillar biodiversity in tropical green habitats. Scientific Reports 2020, 10, 1023. [xxiv] Narango DL, Tallamy DW, Marra PP. Native plants improve breeding and foraging habitat for an insectivorous bird. Biological Conservation 2017;213, 42-50. [xxv] University of California. Pests in Gardens and Landscapes. See https://ipm.ucanr.edu/PMG/GARDEN/PLANTS/INVERT/sawflies.html#:~:text=Life%20cycle,and%20emerge%20as%20an%20adult. Accessed 9 September 2023. [xxvi] Summerville KS. Managing the forest for more than the trees: effects of experimental timber harvest on forest Lepidoptera. Ecological Applications 2011; 21(3), 806 [xxvii] Overview. See https://caterpillarscount.unc.edu/#:~:text=Caterpillars%20Count!%20is%20a%20citizen,for%20birds%20and%20other%20wildlife. Accessed 7 September 2023. [xxviii] National Geographic. Dew. See https://education.nationalgeographic.org/resource/dew/#. Accessed 8 September 2023. [xxix] Cleveland Clinic. Arachnophobia (Fear of Spiders). See https://my.clevelandclinic.org/health/diseases/21852-arachnophobia-fear-of-spiders#:~:text=What%20is%20arachnophobia%3F,or%20more%20things%20or%20situations. Accessed 8 September 2023. [xxx] The Recovery Village. Fear vs. Phobia: What’s the Difference? See https://www.therecoveryvillage.com/mental-health/phobias/fear-vs-phobia/#:~:text=Fear%20is%20a%20natural%20emotion,the%20actual%20danger%20they%20present. Accessed 9 September 2023. [xxxi] Arabeus diadematus – very common in gardens throughout UK. [xxxii] Argiope bruennichi – look for a zigzag of dense white silk down the centre of the web. [xxxiii] Hyptiotes paradoxus – its web looks like a slice of pizza. Hence the name of the spider. [xxxiv] Uloborus plumipes – has set up shop in garden centres and was imported from The Netherlands. [xxxv] Hendry L. Spider webs: not just for Halloween. See https://www.nhm.ac.uk/discover/spider-webs.html#:~:text=Spiders%20build%20webs%20all%20year,the%20transparent%20nature%20of%20silk. Accessed 8 September 2023. [xxxvi] Button J. Spider Season: When are spiders most likely to enter UK homes and how can they be prevented? 27 September 2022. See https://www.newcastleworld.com/lifestyle/homes-and-gardens/spider-season-when-are-spiders-most-likely-to-enter-uk-homes-and-how-can-they-be-prevented-3816033#. Accessed 8 September 2023. [xxxvii] Wikipedia. Spider mite. https://en.wikipedia.org/wiki/Spider_mite. Accessed 8 September 2023. [xxxviii] Prestige. Spider Mites or Spiders. See https://www.prestigestt.com/glossary/spider-mites-or-spiders/#:~:text=With%20some%20careful%20observation%20it,spider%20mites%20in%20the%20web. Accessed 8 September 2023.
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