Dear Readers, the brown and distorted leaves of the horse chestnuts on Hampstead Heath tell their own story of how things have changed during my lifetime, and particularly during the last twenty years. If you had a look at the short film in the blog that I did a few days ago, you’ll have seen that loveliest of things, a horse chestnut in full leaf. These days, we’re lucky if they get past flowering before the leaf miners and the various fungi that attack the tree have turned those big palmate leaves into a patchwork of brown and yellow, before they shrivel and fall.

Horse chestnut leaves, July 2022

It’s said that these various ‘pests’ won’t kill the trees, but I do wonder if the leaf damage over successive years weakens them. After all, most of them are relatively recent. The leaf miner, a tiny moth whose caterpillars actually live between the layers of the leaf, was only sighted for the first time in 2002. Since then it has been working its way steadily across the country, until most of our horse chestnuts are a tatty mess long before they should be losing their leaves. The trees are also producing fewer and smaller conkers, which is a shame for any remaining children who like to play with them. However, there is evidence that blue tits are starting to get the hang of feeding on the larvae, and it’s hoped that parasitic wasps might recognise this handy food source, as they often do. Let’s hope it’s soon.

In ‘Nature’s Calendar’, Rowan Jaines tells the story of how the horse chestnut first arrived in the UK. It’s been here long enough for many people to think that it’s a native, and to be honest I thought it was another one of the things that the Romans had done for us, but no. The first record of the Horse Chestnut in Europe is from 1576, when the tree was planted in the gardens of the imperial palace in Vienna. It was so impressive that it spread across the gardens of the continent, with two trees arriving in France in 1615. One of the trees lived in the grounds of the Hotel Soubise in Paris until its death in 1840, while a second lasted until 1767 in the Jardin des Plantes. Louis XIV loved the tree so much that he ordered avenues of the trees to be planted at Versailles, assuring that the tree would be fashionable, and would spread across the estates and gardens of the rich throughout the eighteenth century.

However, its place of origin was something of a mystery. The first trees planted came from Turkey, and horse chestnuts were thought to be of Asian origin right up until the nineteenth century, when it was found that their home range was actually in the Balkans, in the mountains of Bulgaria, Albania and Greece.

Horse chestnut bud

However, what’s very interesting to me is how the tree got the name ‘horse chestnut’. I always wondered if it was something to do with the shape of the bud, which could possibly look like a horse’s hoof (if you squint). However, it appears that the conkers were ground up and used as medicine for coughs and chest complaints in horses as far back as the sixteenth century. In fact, chemical compounds in conkers have been found to control inflammation and swelling and reduce the accumulation of the fluid that causes the horses to cough, so there is scientific evidence for centuries-old practices. I always find it heartening when the skills of generations stand up to twenty-first century scrutiny, as many often do. Let’s celebrate the horse chestnut, that most impressive of trees, and let’s hope that nature soon finds a way to balance the effect of its parasites.

Horse chestnut flowers

Frogs in the pond in 2022

Dear Readers, this has to be my favourite New Scientist headline so far this year. See what you think:

Frogs have attempted sex with other species for millions of years.

Well, I don’t know about you but this seems like a pretty rubbish life strategy, though my observation of the frogs in my garden strongly suggests that this could be true. At the height of the breeding season, the frogs attempt to mate with other male frogs, they mob the females and if there were toads or goldfish in the pond I’m pretty sure that they’d try to mate with them as well. Frogs have been observed engaged in sexual congress with boots, turtles, dead frogs and frogs of a completely different species. 

One theory is that in situations of explosive breeding, where lots of males emerge from hibernation at once and there are relatively few females, grabbing whatever you can find and hanging on like billy-o would usually pay off. Frog mating involves amplexus, in which a male grabs a female and hangs on with a specially adapted ‘thumb’. He then waits until the female lays her eggs and fertilises them as they emerge, but a female might take hours, or even days, to be happy enough to lay, so he has to be capable of staying with her, and fending off other males, for that whole period. Possibly the occasional male grappling a stick or a goldfish is a small price to pay for the chance of successful reproduction.

What is interesting, though, is that even frogs that have different mating strategies from the ones in my pond also display what scientists call ‘misdirected amplexus’. Tree frogs, for example, sit around and call to attract a female, who comes to them, and who gives the male a little pat on the shoulder to indicate that she’s happy to mate, and yet even these species occasionally mate with the wrong species. What’s going on? Evolutionary biologists have studied the behaviour across 159 frog species, and have concluded that even the earliest frog species, dating back to some 220 million years ago, also made these kind of mistakes. It could even go back further, to the ancestors of frogs, salamanders and a type of amphibian called a caecilian.

Presumably if this behaviour was catastrophic, frogs wouldn’t have become the extremely successful and widespread species that they are today, but there is bad news. The incidence of frogs getting it wrong seems to be more widely reported in the 21st Century than previously, and scientists are concerned that habitat destruction, drought and noise might all be contributing to frogs not meeting enough females, and becoming more generally confused. Add this to the chytrid fungal disease which is causing the decline and even extinction of many frog species, and what can seem like a harmless quirk of behaviour could have serious implications for these fascinating animals.

Dear Readers, I was journeying home to East Finchley on the 263 bus today when I noticed how many of the London Plane trees that line the route had been in effect ‘pruned’ by the double-decker buses that pass under them. Nowhere is it clearer than with the trees in the photo above, where the ones to the left have all been ‘topiaried’ to the exact height of a London bus. However, while the smaller twigs and leaves are presumably safely removed by a bus roof, there must surely be a more managed programme of tree maintenance to make sure that passing omnibuses aren’t ‘scalped’ by the branches.

In the olden days (i.e 1943) there was a special open-topped tree-lopping bus. Have a look at this short film. What is a marvel is not only the low-tech tools used (I have most of them in my garden shed), but that the horse chestnut being pruned is in such excellent health. And I love the bit at the end where the ‘tree-loppers’ throw conkers to the waiting urchins.

Lopping Trees for London Buses (1943)

You may sometimes see signs on the trees lining the road, saying instructive things like ‘Tall Trees’. Some of the Plane trees that line North Hill in Highgate really are tall.

Travelling at speed on a bumpy road on the 263 bus.

However, signs are not always enough: in 2015 a double-decker managed to collide with a Plane tree on the Kingsway, close to Holborn, and the roof was neatly sliced off. Five people were injured, fortunately none of them seriously, though I imagine that they didn’t travel on the top deck for a while. Apparently there was a sign saying ‘Overhanging Trees’ on the tree in question, but clearly it wasn’t enough.

Photo by Stuart Coates (Twitter)

In 2012 there was a similar incident in Croydon, where again the roof was ripped off. I wonder if double-deckers are actually designed in this way? Presumably taking the roof off is better than it collapsing inwards on to the passengers. Any bus nerds out there who would care to enlighten me (and I use the word ‘nerd’ with the greatest of respect, being a bug nerd myself).

The 119 bus that was de-roofed in 2012 in Croydon (Photo from https://www.standard.co.uk/hp/front/tree-rips-roof-off-london-bus-6847204.html)

There is a regular programme of pruning, pollarding etc for London’s street trees, with the condition of the trees assessed, and rotten branches and other dangerous protuberances removed where necessary. This does leave the question of how drivers manage to drive into trees, though I imagine that a branch at the height of the roof is not easily assessed from the point of view of the driver’s cab, especially as they have to do everything these days – on a one-person bus the driver is expected to take fares, sort out any passenger nonsense (of which there is plenty) and drive through the streets of London which often resemble nothing so much as one of those live action video games where people jump out into the road, throw their car doors open without looking, and occasionally stop dead in the middle of the road to check something on their mobile phones. Thinking about it, I’m amazed at how rarely buses collide with trees. It’s something of a miracle.

The avenues of London Plane trees and Limes are a cool and welcome sight as the 263 crests the hill at Highgate and heads towards East Finchley station, and long may they remain so, even if their lower branches have to be trimmed to a convenient height. What venerable trees some of these are!

Dear Readers, I was visiting a friend in Walthamstow today when I passed a wall covered in ivy flowers, and I thought I’d stop and have a quick look just in case there were any ivy bees. And indeed there were! The ivy was abuzz with honeybees, hoverflies, bumblebees, ‘ordinary’ flies and a few wasps (of which more later). But of course I was looking for these little stripy critters, and there they were. In comparison to honeybees they are slightly smaller, and somehow ‘zippier’ – they can also stand up for themselves very ably, and weren’t the slightest bit fazed by the presence of a queen bumblebee about four times their size.

If you look closely at the photo above, you can see a) that the stripes on the abdomen really are very distinct. But I think an interesting diagnostic feature might be those little hairy back legs. In social bees, you often see all the pollen bundled together in a structure called a corbicula (literally ‘little basket’), but solitary bees like Ivy Bees don’t have these, and so they have to collect the pollen on their tummies (as in leaf-cutter bees) or on their legs.

In the photo below, if you look at the top left you can just see the backside of a honeybee – note that the stripes on the abdomen are not as distinct as in the ivy bee at the bottom left. You can also see a bright orange ball of pollen attached to one of the honeybee’s legs.

Don’t ask me who the critter on the bottom right is. S/he rather photobombed the scene.

So as you can probably tell I am very excited about finding these attractive little bees again, and to see them foraging so urgently. They must be making their nest tunnels somewhere fairly close by, probably in a garden that doesn’t even know that they’re there. This is the joy of having the time to stop and observe the goings on in nature, even if it’s just for five minutes (and even if it involves blocking the pavement and attracting strange looks from passersby).

Finally, I mentioned wasps, and there are a few about this year. The nests are starting to break up, and the wasps are footloose and fancy free, which is why they’re turning up at picnic tables. But some nests must still be in operational order because some of the wasps were still hunting for protein (which they feed to their larvae) rather than just snacking on the sweet stuff. One wasp was cruising around when it spotted some unfortunate fly trussed up in a spider’s web that was strewn across the ivy. The wasp not only approached and tried to cut the fly out of the web but, when it was unsuccessful, it flew through the web, making quite a kerfuffle of buzzing in the process, and then tried to extract the fly from the opposite side. It was only the sudden appearance of the spider that deterred it and sent it on its way. You might remember that I spotted a wasp actually going into an ants’ nest to remove larvae a few years ago, but this was new behaviour for me. Have you spotted wasps doing anything surprising? I suspect these insects are much more adaptable and opportunistic than we give them credit for.

And I promise to move on from ivy bees tomorrow. If I can tear myself away.

Ivy Mining Bee (Colletes hederae)

I am following the 72 microseasons in Nature’s Calendar as inspiration for the next twelve months – let’s see what we can find!

Dear Readers, I spotted my first Ivy Mining Bee in 2019, on some mature ivy in the gardens of the National Archives in Kew. How exciting it was! These little bees first arrived in the UK in 2001 and have made themselves very much at home. Although they look rather like honeybees, ivy bees have a much clearer set of yellow and black stripes on the abdomen and ginger hairs on their thorax. I took the photo above with my phone (and this is an indication that you should always have your proper camera handy – you never know when something exciting is going to pop by)

Here is a much better photo. If you have ivy, and if it ever stops raining, have a look and see if you can spot some Ivy Mining Bees. They are currently only found in Southern England, but are travelling further north every year.

Male Ivy Mining Bee (the female is very similar) (Photo by By Charles J. Sharp – Own work, from Sharp Photography, sharpphotography, CC BY-SA 4.0, https://commons.wikimedia.org/w/index.php?curid=51348998)

When you notice ivy bees, you can be sure that autumn  is underway: this species is the very last to emerge from the nest each year, and the adults will only live for about six weeks. As the name suggests, they feed almost exclusively on ivy flowers, and use the pollen to feed their larvae. Ivy Mining Bees are solitary, with each female bee making a tunnel in soft or sandy soil, and laying a single egg in each one, which will be provisioned with the pollen. Once complete, each tunnel is sealed and the female, her job done, will die. Although the bees are solitary (inasmuch as they don’t make a communal nest) there can be many individual tunnels at a suitable site.

In August, the larvae start to hatch as adult bees, with the males hatching first. The males hang around waiting for the females to emerge a few weeks later (they time their emergence for when the ivy is starting to flower). When the females appear they produce a pheromone so overwhelming that many lust-crazed males may pounce upon a female, forming a mating ball. This reminds me of the frogs in my pond, where again the males emerge (this time from hibernation) first, and hang around waiting for the females (who seem to hibernate elsewhere in the garden) to turn up. Again, a number of males may try to mate with a single female.

A mating cluster of Ivy Bees (Photo by By Charles J. Sharp – Own work, from Sharp Photography, sharpphotography, CC BY-SA 4.0, https://commons.wikimedia.org/w/index.php?curid=51349000)

I’ve written before about how invaluable ivy is, in spite of its reputation as a destroyer of trees and buildings. There is a clump of it in a front garden just up the road from me, and I noted 6 species of insect feeding from it even on a blustery day like today. So I wanted to mention another insect that, if you’re lucky, you might see on ivy flowers: the golden hoverfly (Callicera spinolae).

Golden Hoverfly (Callicera spinolae) Photo By Barry Walter – https://www.inaturalist.org/observations/34871549, CC BY 4.0, https://commons.wikimedia.org/w/index.php?curid=132624690

This is a very handsome fly, and sadly rare too, so you will  be lucky to see one – in the UK it’s mainly confined to East Anglia. The adults feed on ivy, as the name suggests, but the problem is that the larvae (like the larvae of so many hoverflies) need wet rot holes – areas of damaged and decaying wood that hold water. The larvae develop in these miniature pools, feeding on bacteria. This kind of habitat is found largely in ancient deciduous woodland, where fallen trees are allowed to remain, and where there isn’t an urge to cut things down and tidy things up. As we all know, these places are becoming rare in the UK. The Golden Hoverfly has only been seen in four locations in the past ten years, but it could be that it is under reported because it spends most of its time either in the canopy or trying to find places to lay eggs. Your best chance of seeing one is to keep an eye on those ivy flowers. Fingers crossed! And if you don’t see a Golden Hoverfly, there are a whole host of other pollinators (including Red Admiral and Holly Blue butterflies) that make good use of the late pollen and nectar that ivy provides. It’s always worth stopping at flowering ivy to have a look.

Honeybee on ivy

Wasps on ivy

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Dear Readers, there can be few flowers that are as spectacular as the Oriental  Lily, and I was gifted some last week when I retired from work. They are extraordinary blooms: some people think that they smell of plastic but these particular ones seem to have a deeply spicy scent, with more than a touch of cloves about them. Interestingly, when a lily that looked like the Stargazer but had no scent was developed, the breeder went out of business, so clearly those who like the scent are in the majority.

The pollen is poisonous to cats – if it gets onto the fur and the cat licks it off, it can cause kidney failure. Fortunately, my elderly cat can no longer be bothered to jump onto anything higher than the sofa, so I can enjoy my lilies without having to worry.

Willow the cat. 16 years old this year!

Stargazers are a specific form of the Oriental Lily – they appeared for the first time in 1974 by California breeder Leslie Woodriff. Woodriff wanted to create a flower that looked upwards, rather than drooping like so many lilies. The original Stargazer lily was mostly pink in colour, as in the photo below, but since then pure white and pink-tinged varieties have been bred. I rather like the delicacy of my pale pink flowers. Plus, do you think there’s the merest touch of ‘Little Shop of Horrors’ about the one below? It looks very slightly hairy to me, which is a little off-putting.

Original ‘Stargazer’ lily (Photo By Jim Evans – Own work, CC BY-SA 4.0, https://commons.wikimedia.org/w/index.php?curid=58312801)

Although they look so delicate and exotic, Stargazer lilies are reputed to be relatively easy to grow. Easy, that is, until this little chap comes along.

Scarlet lily beetle (Lilioceris lilii) Photo By Charles J. Sharp – Own work, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=28705466

I think that these are very attractive-looking beetles in their livery of red and black, and note the little indentations in their wing cases (elytra), as if someone has picked them over with a tiny sharp stick. Alas, their larvae eat the leaves of all lily and fritillary species, and they can make short work of your prize specimens. In Europe, the beetle larvae are preyed upon by a variety of parasitic wasps, which helps to keep things in some kind of balance. In North America, however (where they were imported in garden soil) there are no predators at all, and so they are more of a nuisance if you like growing lilies.

Incidentally, a distressed lily beetle can let out a loud squeak if it feels threatened by rubbing its legs together, which may be enough to deter an eager bird (or even an eager gardener). It can also play dead (known as ‘thanatosis’), which is a popular tactic in the invertebrate world.

Back to our lilies.

One thing that lilies illustrate rather beautifully is the way that plants reproduce.

Photo by By JJ Harrison (https://www.jjharrison.com.au/) – Own work, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=5920599

1. Stigma – this is the tip of the female part of the plant. This is often sticky, and this is the spot where the flower will receive pollen, either from a passing bee or other pollinator, or blown in the wind. Note that it’s held high above the pollen-producing organs – this lessens the chance that the plant will be self-pollinated. Some stigma are also able to reject pollen which is too closely related, or which is from the same plant.
2. Style – this is the tube down which the pollen will pass in order to connect with the ovule, which is deep in the heart of the plant. Once there, germination will occur and a seed will be created.
3. Anthers – these are the parts of the plant that produce pollen and, together with the filaments (4) which support them form the stamen, usually considered to be the male part of the plant. Lilies produce a lot of pollen, as anyone who has tried to wash it out of a white teeshirt will concur.
4. Filament (see above).
5. Tepal – in many plants, you get petals and sepals – the sepals are the green protective parts that surround the petals when they are developing in the bud, and which are found at the base of the flower once it opens. Lilies, however, don’t have any differentiation between the petal and sepal, so their petals are called tepals. Simples! And if you think there’s a poem in all this, you’re probably right.

In the Victorian Language of Flowers, lilies were said to represent love and affection for your loved ones, so I am especially touched to have received a whole bunch of them from my workmates. They are also associated with funerals (which may be another reason why they’re sometimes disliked), but as they are meant to show that the soul of the deceased has been returned to a state of innocence I think they are wholly appropriate.

And finally, as usual, a poem. There’s something about this short poem by Ben Jonson that I’ve always liked – each line a new image, and the whole thing so sensual and full of life. He might have been a man of the 16th and 17th centuries (1573 – 1637) but he knew how to live, did our Ben.

Have You Seen
but a Bright Lily Grow”

Ben Jonson

Have you seen but a bright lily grow
Before rude hands have touched it?
Have you marked but the fall of snow
Before the soil hath smutched it?
Have you felt the wool of beaver,
Or swan’s down ever?
Or have smelt o’ the bud o’ the brier,
Or the nard in the fire?
Or have tasted the bag of the bee?
O so white, O so soft, O so sweet is she!

Dear Readers, has anyone else noticed how the starlings seem very restless at the moment? Here in East Finchley they’re sitting on the chimney pots and aerials, singing and chattering and occasionally flying into the air, circling and settling back down. I noticed a similar thing last autumn, but hadn’t put two and two together.

I am wondering if these starlings are experiencing Zugunruhe, which roughly translates from the German as ‘migratory restlessness’. I’ve noticed the same in birds such as swallows and house martins, who seem to be almost crawling out of their skins in the days before they migrate, as if they don’t know what to do with themselves. The phenomenon was first observed when migratory birds were kept captive – it was found that they would not only orientate themselves in the direction in which they would normally fly, but that the length of the period of Zugunruhe would be related to the distance of the normal migration.

What’s interesting is that the majority of starlings in the UK no longer migrate (though they are joined in the winter by birds that migrate from northern Europe and return south in the spring). However, it’s been shown that even birds that are now resident seem to have some sort of ancestral memory of the days when they used to take flight in the autumn for a long trip south. Studies have shown that most birds have the potential for migration, which makes a lot of sense: if the food runs out in the area where you live and breed, you might need to move in order to raise your young successfully. Various bird species are changing from being migratory to being resident – some blackcaps, for example, now spend the winter in the UK, a result of milder winters and increased levels of garden feeding. Some birds are not migrating as far as they used to, because food is available closer to home (again, a result of fewer freezing winters). All in all, nature is in a constant state of flux, which is exacerbated by all the human-made changes that are going on. Just as well our feathered friends are as adaptable as they are.

Anyhow, the starlings have now wheeled away, probably to seek out some suet pellets or to sit in one of the plane trees on East Finchley High Street for a good old whistle and bicker. And I need to get stuck into my brand new Open University course (‘Environment: Sharing a Dynamic Planet’), which could not be more relevant. I shall keep you posted of how it’s all going!