From across the vegetable garden, it’s a ghost tree, a solarised photograph of a tree against a green background of sycamore and hawthorn. Each year the leafy tips of this bird cherry are covered in the taut spun tents of ermine moth caterpillars, Yponomeuta evonymella. This year the entire tree is encased in a pale, sheen-like opaque clingfilm.
I look up its trunks and they are silvered to the top. The work of the caterpillars has encased foliose lichens, trapped fallen nascent cherries and shrouded the trunks in stockinged silk. It’s eerie and fascinating, and more of a spectacle than in most years; the moths breed in boom-and-bust cycles.
Twin trunks growing close together have formed a cleft and this is filled by white pupae in neat parallel lines, like shoals of fish swimming in the same direction. I press the tensioned silk with my fingertips and it bounces back, a few bodies still moving beneath it, spinning as they go. Where I break it, there are layers and layers of gauze. The caterpillars’ droppings have congregated in tide lines, peppercorns coloured dark brown through ochre to buff.
Beneath the tree, a table and chairs have been wrapped together and a line of rosemary bushes is enmeshed in film. Blue tits work their way through the bare branches above, picking off any caterpillars that are unprotected. Flying between bird box and cherry, they are raising their brood on this easy bounty.
Inside their webbing, the caterpillars pupate. Within a week a flush of leaves will appear on the branch ends. No longer being munched, the tree recovers unharmed; it would not be in the moths’ interest to kill their host. After a short pupation, many thousands of moths will emerge, their slender white wings studded with five rows of black dots.
Night-flying moths, the adults, have a further defensive strategy. Because they are deaf they cannot listen for approaching bats, so they produce a continual series of ultrasonic clicks from their hind wings, imitating those made by toxic moths.
Soon the adults will emerge and, when I do my weekly count of moths at the light trap, there will be a dramatic increase in recorded numbers.
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