It was love at first sight; one of those eyes across the Park moments. Standing as sentinel in an open wooded habitat amongst scarlet Pin Oak and yellowing Salix, this tall dark stranger had a monumental Gothic presence. High up in the canopy, triangular whispering leaves were hanging on to their lime-green vestments well on into late November. Aside from a mossy North face,1 the bark was intensely grey-black and most alluringly tactile. It was not hard to imagine a volcanic crater secreted in the crown, whereby larva had oxidised down in overlapping, butted verticals.
Given the bark’s colouration, I had first assumed it to be one of the UK’s rarer native Black Poplars but after a deal of research, finally nailed it down as Populus x canadensis (I think correctly although identification of Poplars requires a somewhat specialist knowledge!). Hybridised in the 18th Century from Black poplar (Populus nigra) and the American Eastern Cottonwood (Populus deltoides), the Black Italian Poplar is quite significantly taller than its Populus nigra parent. Having a more compact crown of upward growing branches, the strongest identification comes from the long deeply furrowed trunk, devoid of the tell-tale knobbly bolls or bosses. The popularity of this faster growing tree increased in the 19th Century where its poorer quality timber was appropriated for the more utilitarian production of matches, crates, clogs and flooring.
Being such an impressively healthy specimen of Poplar, I was surprised to see a tumorous outgrowth where trunk and root met in the grass line. Closer inspection of the deformity revealed woodworm-type bore holes which made me wonder if the tree was rotting from the base up. A quick google of wood borers on Poplar however revealed that in fact these were most likely to be the exit holes of a rather scarce and unusual UK insect: Sesia apiformis or Hornet moth.
In striking vespa colouration, this British clearwing moth lives and loves in around Poplar trees. Eggs are laid at the trunk base where the hatched larva feed by boring into the bark and eventually cocooning themselves in the tunnels. Taking between 1-2 years to reach maturity, the adults are on the wing in summer, with a jagged flight pattern that completes their hornet mimicry. They may be spotted at rest low down on the trunks in early to mid morning but are rarely seen north of the Midlands.
Sesia apiformis images from Wikipedia
Evidence from the timber industry pinpoints Sesia apiformis as a significant pest of Poplar but there is a difference between the goals of commerce and arboreal ecology. A summary review of decade old studies by Eureka Mag indicates that human activity and climatic variations may be at the root of the Populus dieback problem:
“the moth most likely acts as a secondary agent in tree decline. Up to 53 per cent of trees with severe dieback occurred in shelterbelts, and many of these sites were situated on reclaimed land or other man-made substrates. The area where dieback has been most prevalent is one of the hottest and driest parts of the UK, and the reports of dieback in Poplar and the apparent increase in S apiformis activity, follow particular dry springs and early summers.” 2
Poplars are often associated with river banks although many eke out an existence in non riparian zones, including industrial cities (e.g. the Manchester Poplar hybrid). This Black Italian Poplar is thriving in it’s Hyde Park setting perhaps because it is protected by the little gnarled tree Dryad which has formed from the activity of the Poplar loving Hornet moth. I shall revisit in Spring and Summer for an update.
Postscript: For my own edification, I aim to do a collection of Tree ID posts, in and around London. Next time: The Black Poplar – much nearer home than I would have expected….
1. Moss and lichen growth on tree trunks indicate a northern direction – a helpful bushcraft tip if ever you are lost in the woods. On this tree the bat box has thus been placed to the east – not the best locale given that Bats need the warmth of a south facing shelter.
2. Eureka Mag: Sesia Apiformis
Identifying ClearwingsUK Moths
And finally… A delightful video of the Clearwing Moth mating ritual – a rather long and haphazard love affair set in the slightly artificial setting of a Butterfly farm but the shots are magnificent.