Country diary: what’s behind this silken grey cloud?

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Foxhole, Norfolk: The spindle ermine moth is a beautiful species. Its caterpillar will strip this tree bare in a writhing mass

Spindle ermine webbing on a tree. ‘This is an entirely natural, sticky spread of greying silken web.’ Photograph: Kate Blincoe‘This is an entirely natural, sticky spread of greying silken web.’ Photograph: Kate Blincoe

@KateblincoeSat 3 Jul 2021 00.30 EDT

It’s an untimely Halloween prank, surely. I’m walking the tracks and paths where I live, grateful to be clearing my head after going out last night – I’m out of practice. Yet my fuzzy brain is not imagining things. A small bushy tree that last time looked entirely normal is today shrouded in cobwebs. For a second, I wonder if it’s been netted, in that awful modern way, to prevent birds nesting. But no, this is an entirely natural sticky spread of greying silken web.

And the bush appears to be moving. I step closer to find a squirming, squiggling mass of caterpillars festooning its branches and twigs, most hidden beneath the web as if trapped inside. There are too many to count: hundreds, each about 2cm long. Most are yellowish, some a grubby grey, all with a neat black spot on each segment. The web is dotted with their excrement. En masse, they make my stomach turn, even though I’m fascinated.

The caterpillars are demolishing the leaves, stripping them bare, but enough remain, with a few white flowers, to see it is a spindle tree. In autumn it is decorated not by caterpillars but bright pink and orange berries. According to Flora Britannica, the wood was used more for skewers than spindles. It means I can fully ID the species of caterpillar as spindle ermine moth – utterly dependent on this one food plant.

Spindle ermine caterpillars.‘The caterpillars are demolishing the leaves, stripping them bare, but enough remain, with a few white flowers, to see it is a spindle tree.’ Photograph: Kate Blincoe

Under cover of numbers, and protected by the webbing, each caterpillar will gorge itself before pupating in a silken cocoon. Then, an attractive white moth, spotted with black, will emerge to mate. The females will lay eggs on the spindle for the cycle to begin anew.

In that perfect natural synchronicity that is threatened by climate chaos, the caterpillars emerge when the spindle is in full leaf and baby blue tits are hatching, and in need of an abundant juicy meal. If the parent birds can navigate the sticky web, that is.

I return over the coming days. The web grows and thickens, becoming opaque, until not a leaf remains. Amazingly, the tree will recover from the onslaught, weakened but unharmed. A week later, the grey shroud is still there, but only a stray caterpillar or two can be seen.

Country Diary is on Twitter at @gdncountrydiary

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