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Murder at the Garden Pond: Thalia dealbata – the (not very) beautiful assassin

An evergreen, marginal aquatic perennial forming a clump of long-stalked, erect, narrowly ovate leaves to 40cm in length, covered with white powder, and slender stems bearing panicles of purple flowers 2cm across’. This, from the Royal Horticultural Society, neatly sums up the rather statuesque plant that we encountered in Beth Chatto’s garden last summer: Thalia dealbata.

As per usual, when in gardens we seek out insects to photograph and were immediately aware that this plant was covered in SO many pollinators. But dead pollinators. On closer examination, each flowerhead was actually riddled with corpses – hoverflies, lacewings, bees, wasps and blow flies, amongst others – a glistening mortuary for those valuable garden assistants, pollinators and predators alike, all stuck headfirst into the mouths of their nemesis.

The scale of the carnage was, quite simply, shocking. Some, still alive, like this Honeybee we managed to release, but most were dead. Lost to the world.

Reference to the internet shows this is a recognised phenomenon. The plant has no reason to kill its visitors – it doesn’t digest them like a truly carnivorous species: it seems that the flowers have an elastic style, used in explosive pollination which can and does trap insects.

In its native central American/southeastern USA range it is normally pollinated by large and powerful Carpenter Bees, capable of extricating themselves from the flower’s fatal embrace. Anything smaller is trapped and starves, mere collateral damage, cannon fodder in the battle for life.

 

But at times of an Extinction Crisis, that is one pressure our array of pollinators, necessary not just for the plant’s but for our species’ continued existence, can do without, dozens of pollinator lives being extinguished unnecessarily for each flowerhead. We raised our concerns with the Beth Chatto gardeners, and they promised to investigate, perhaps to remove the spikes of (to our eyes, rather unlovely – they often don’t seem to open fully) flowers, leaving only the stately leaves to give emergent architecture to the water margins.

And to their credit, the Beth Chatto online sales catalogue does at least draw attention to this antisocial behaviour attribute of Thalia: ‘Please note that the plant has an unusual mechanism for pollination which results in some pollinating insects remaining trapped within the flower, where they can perish. Hover flies appear the most affected.’

No other suppliers that we came across made any such references to the ‘special properties’ of Thalia, so we started a bit of a Twitter campaign to raise awareness, and perhaps get restrictions on the sale of the species, or to at least persuade suppliers to inform potential customers of the plant’s fatal attraction. And perhaps in response to this, we note that six months on, the RHS website now contains the following sentence: ‘Although not carniverous [sic] as such, this plant may trap and kill small insects such as hoverflies and small bees during the pollination process.’ Not the unequivocal recommendation not to buy and grow it that we might have hoped for, but a start nonetheless…

The RHS also provides a list of recommended stockists, of which six are noted for Thalia, one in France and five in the UK (including Beth Chatto’s). Two of those seem no longer to list it on their catalogues, but that still leaves three well-known British aquatic plant suppliers who do without hesitation, one even noting it is ‘much frequented by butterflies, moths and other pollinators’ without giving the full story. And of course other UK suppliers are available, though in the first three pages of a Google search, none referred to Thalia’s nasty little habits, save for World of Water Aquatic Centres which in its information table asks ‘Perfect for Pollinators?’, and gives the answer ‘No’, albeit without explanation.

We shall be contacting suppliers to try and persuade them to at least mention this issue, if not withdraw it from sale , in the hope that insects can be saved and eco-conscious gardeners are not upset at the behaviour of their latest purchase. And future updates to this blog may include a ‘name and shame’ as well as a ‘Hall of Fame’!

#WildWivenhoe Botany & Bug Walks: February awayday to the Naze

What could be better – a walk on the beach on a sunny afternoon, time to scrabble about and get dirty hands in the search for fossils and other beach treasures, followed by tea, cake and chat in the warm?  Our intrepid Bug-and-Botanists all had a whale of a time on Saturday at The Naze, and despite there being a distinct lack of botany (except of course Gorse) or bugs to admire, there was plenty of ‘nature’ to enjoy!

Standing on the beach looking at the cliffs, you really are looking back many millions of years in time.  The whole area, a Site of Special Scientific Interest, is one of the finest geological sites in Britain, comprising layers of London Clay, topped by Red Crag.

The stunning redness of the Crag is due to oxidisation of the sand and fossil layer laid down over 3 million years ago when Walton was, as now, at the edge of the sea, just prior it being engulfed in the turmoil of the last Ice Age. Fossils of many kinds and shell debris can be readily be found on the beach, most stained an attractive red colour, distinguishing them from otherwise-identical modern shells.

A combination of the seeping of rainwater downwards, lubricating the clay surface, and storm wave pressures makes the whole area prone to landslips and substantial coastal erosion, which although a delight for geologists and fossil-hunters, nevertheless is extremely worrying for those with buildings atop the cliffs!  One example of course is the famous Naze Tower, a 300 year old landmark, built by Trinity House for navigational purposes and which today is a popular art-gallery and tea room.  Some years ago a local dispute raged as to what to do – completely surround the whole Naze with a sea defence?  (extremely expensive and would prevent geological discovery and the ‘production’ of sand which feeds our local seaside resorts), or let the whole area eventually fall into the sea?.  A compromise was sought and about ten years ago an additional 170 metres of defence was built.

Now known as the Crag Walk, this allows a safe walkway, and provides a chance to study the cliffs at close quarters, whilst learning about the geology and wildlife from interpretation boards. It also protects the area immediately below the tower.

And so to our beachcombing….many delights awaited the patient explorer, but sadly no 50 million year old shark’s teeth,  from inhabitants of the subtropical London Clay lagoon which then covered most of what is now Essex, were forthcoming this time.  Our photo shows one that ‘we found earlier’ on a previous visit….

‘Boring piddocks’ Chris was heard to exclaim at one point….to whom or what was he referring?  Turns out Piddocks, also known as Angels’ wings, are attractive shells which bore vertically in the soft London Clay, making perfectly round holes as they do so.  These examples (above left) are modern, as is their holey now-deserted home in the right hand image. Other delights in this photo include ancient pyritised wood (turned to ironstone), and fossilised poo known as ‘coprolite’. Fifty million years old!

The ubiquitous left-hand coiling whelks Neptunia contraria are interesting as most gastropods coil in a dextral way;  these left-handers from the Red Crag seas can be dated at over two million year old.  It’s hard to get your head round numbers like this!

Although quite slippery on the London Clay platform, areas of sand became more accessible as the tide receded and we were particularly struck by the beautiful dendritic drainage tree-shapes in the sand.  So  much to see, but the time came to leave the beach and we finished our session with a cliff-top walk, admiring features on the skyline, and taking the opportunity for some wildlife-spotting:- a Common Seal bobbing along, Brent Geese feeding and a perfect chance to see a beautiful male Sparrowhawk at rest on the Crag.

We look forward to kicking off our season of Botany and Bug Walks proper in April, and hope that some of you will be able to join us.

Beth Chatto Gardens – sunlight and shadows

The winter thus far remains stubbornly at arm’s length, save for a few frost-washed mornings. The crisp blue light of a midwinter morn has been hard to come by too, temperatures held up and spirits lowered by seemingly unremitting gloom.

But at last today the skies cleared and the garden once again came into its own.

Sunlight and shadows….

Seedheads and sprinkles…

Subtle splendours…

And scentwaves and snowdrops.

 

Beth Chatto Gardens: the reawakening of the year

‘Reawakening of the year’ hardly seems appropriate, as hitherto the winter slumber has been barely discernable, with few frosts, and bees and other insects around us all the time. As worryingly now seems to be the norm.

Maybe ‘renewal’ is a better term: last year’s leafy growth is playing its final role as a blanket protecting the coming seasons’ primordia from environmental extremes, before breaking down into the nutrients they need to fulfil their potential…

…while tussocks of grass and other plants again provide shelter for overwintering invertebrates, and sources of food to seed-eaters. In too many gardens – happily not Beth Chattos – these would have been ‘tidied up for the winter’.

New spring greens are already coming through, with added colour from variegations and coloured bark, perhaps more obvious and appreciated at this time when flowers are at a premium.

And likewise now is the time to appreciate the trees for what they are, liberated from the distraction of blowsy flowers all around. Standing for decades, centuries even, like old furniture they are so often ignored, but what a delight they are, hinting at the riches they have already given us and promises for the future.

Structure and texture are best appreciated when the sun shines, and this is when their trunks play a role for the few insects on show, sheltered spots for basking flies, even on a cold day like today.

On a warmer day, no doubt many more insects would have been evident, roused from winter torpor and needing to feed to replenish resources for any cold snaps to come. Herein lies the value of a garden: in January, the countryside is pretty much devoid of pollen and nectar sources apart from Gorse. But in a good garden, the ‘winter nectar gap’ can be closed, an essential feature in these times of climatic disruption.

Moreover, some of those plants have a scent that intoxicates even the most jaded human snout, from spicy Wintersweet to rich Witch-hazel, the delicate lily-of-the-valley fragrance of Mahonia to the ultra-sweet wafts of Sarcococca.

 

Identification by Internet…

May 2012, we were undertaking a butterfly transect for the national monitoring scheme within and close to the Great Notley Country Park, near Braintree. An unexpected shower at the end of the transect caught us out, but trudging back damply along the rather unprepossessing-looking hedgerow and track between two intensive arable fields, our eyes were drawn to a mating pair of insects….

Or I should say ‘mating pair’: examining our single photo back home revealed a superb example of ‘two becoming one’, the head (even down to the eye-glint) of the ‘one on top’ actually the pattern on the lone insect’s thorax, as if its head had been cloned there with Photoshop.

But what was it? It seemed to be a sawfly, a type of wasp without a wasp-waist, but after flicking through the paltry coverage of that group in available popular field guides, we rapidly drew  a blank. The 500 or so known species of sawfly in the UK are very poorly known, as all but a few of the more easily recognisable ones are omitted from the guides. Such a collective information gap is very unfortunate, especially when you see that many also have distinctively marked and wonderfully charismatic ‘caterpillars’, or distinctive feeding signs and galls. Just a few are shown below:

Anyway back to our ‘mating pair sawfly’. We were busy, and the photo got relegated to a pending file… until 2019 when scrolling through some of the riches of the internet, we saw something that triggered a lightbulb moment of recognition. Once we found our image, there it was – Pamphilius sylvarum. Except that is a species with records from only nine previous localities in Britain, ranging north to the Welsh borders, near Wrexham, and Sherwood Forest. The sole other Essex record came in May 2019 from Chigwell, in the Metropolitan sector of the county, courtesy of Yvonne Couch. As well as its scarcity, the habitat of ours seemed odd, given its assumed reliance on oak leaves (which its larvae roll up), perhaps in a woodland or woodland-edge context. There were several spindly hedge oaks within a few tens of metres of our specimen, but otherwise just a hedgerow and open arable. A more uninspiring location for such a rare insect is hard to imagine.

Nonetheless, we could not find much about it, nor about potential lookalikes, so I posted the picture on Twitter, and within a day, had the collective thumbs up from such experts as Steven Falk, Andy Musgrove and Andrew Green.

This episode brought to mind a similar finding from the Beth Chatto Garden, near Colchester. On one of our regular visits at the very end of October 2016, insects to photograph were few and far between, but we did find a fly sitting in a geranium flower. Once again, close examination of the photos showed it to be something different, and unknown to us. It had the appearance of a blow-fly, but with markings not unlike a hover-fly, and excitingly striped eyes, more like those of a horse-fly.

Once again scrolling through the internet came to the rescue, suggesting it was the Locust Blowfly Stomorhina lunata, an egg predator of locusts and grasshoppers, normally well to the south of the UK. Perhaps reflecting its spatially unpredictable feeding preferences, it is a known wanderer, including to the UK, albeit rarely, although seemingly increasing in recent years. In fact in the previous year there had been the largest known migratory arrival in Britain to date, one of which was in Essex at Rainham, only the second record for our county. The identity of our specimen was then confirmed by Del Smith, the fly recorder for the Essex Field Club.

Of course we cannot assume either of these rarities are actually as rare as the paucity of records might suggest. Quite likely their distribution reflects the distribution of recorders rather than the species, especially given the lack of popular illustrated insect guides which cover such oddities.

The internet and social media are much maligned, with considerable justification, but they can give access to more information about insects of all sorts than we could have imagined a few years ago, at least for those without easy access to a museum collection. But BEWARE! As noted on the British and Irish Sawflies website, ‘The internet is awash with incorrectly identified sawfly images so it is recommended to avoid identification by Google searches. The image galleries on this website and on the links below are sourced from known and trusted hymenopterists‘.

Therein lies the answers. By all means use the available picture resources to attempt an identification, but one should always give greater weight to expertly determined and curated sources. And then use social or other networks to get confirmation. If forthcoming, then importantly the records should be submitted and captured for posterity, ideally via a web portal such as iRecord. As always, there will be some species whose identity cannot be ascertained definitively from a photo. As ‘ethical naturalists’ who don’t wish to kill things in pursuit of our hobby, knowing and accepting our limitations is crucial.

#WildWivenhoe Botany & Bug Walks: January – trees in winter

January’s walks were short and sweet, and concluded our three ‘Tree-mendous’ winter events. We walked around the edges of King George’s Field looking at winter twigs, bark and tree shapes.

Below is a series of close-ups of Chris’ photos of some of the twigs we looked at, with a brief description:

ASH  Twigs straight and slightly flattened below the buds, which are black and distinctive and usually in opposite pairs.

BEECH  Twigs thin and zigzagged.  The buds are long and slender, with a waxy white tip, and spread out from twig at a 60 degree angle.

HORNBEAM Twigs slender and zigzagged.  Buds long and pointed, like Beech, but appressed close to, even curved into, the twigs.

HORSE-CHESTNUT Twigs thick, with horseshoe-shaped leaf scars.  Buds with large red-brown scales, not yet quite at the stage of developing their characteristic stickiness.

SWEET CHESTNUT  Twigs shiny and markedly ridged, with heart-shaped leaf scars, showing numerous vascular bundle scars.  Buds plump, reddish and sit on ‘shelves’.

OAK  Twigs widely branched, showing numerous pale lenticels (‘breathing holes’)  and often decorated with woody galls.  Buds plump, orange-brown, and clustered and scaly.  The number of visible bud scales is diagnostic of type of oak: fewer than 20, as here, indicates Pedunculate Oak.

SYCAMORE  Twigs greyish, often with ‘wrinkled stockings’, the stacked leaf scars from previous years. Buds large and pale green, in opposite pairs, but with a lovely purple edging and a white fringe. See, even dormant buds can be beautiful and exciting! And you really do not need leaves and flowers for identification: botanists should never hibernate!

We are indebted to The Field Studies Council for their very informative booklet ‘Winter Trees, A photographic guide’ for inspiration and information. https://www.field-studies-council.org/shop/publications/winter-trees-a-photographic-guide-to-common-trees-and-shrubs/