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bramble leaf showing a tunnel, or mine left by a moth larva

Anyone who has spent any time scrutinising a bramble bush at this time of year (is it just me then?) will recognise the squiggly trail left by the caterpillar of a Bramble Leaf Miner Moth (Stigmella aurella).  The moth lays its egg inside the leaf where the larva hatches and slowly snakes its way through the leaf by eating a tunnel just below the outer skin of the leaf.  At this time of year the frosts turn the mines a silvery colour and they are much easier to find.

more leaves showing the trails left by leaf mining moth larvae

As the caterpillar chomps its way through the leaf tissues it inevitably grows, and consequently the tunnel gets bigger and wider.  You'll notice inside the tunnel the caterpillar leaves behind a little dark line of what entomologists politely call "frasse" (it's poop), and this shows up well if you hold the mine up to the light (free lightbox here).

Eventually the caterpillar reaches full size and pupates in readiness to emerge as an adult moth.  You can sometimes see a small slit in the largest end of the tunnel where the insect would have left.  The adult moth has a silvery sheen to its wings and a cream coloured streak running across the middle of them.  You might see one as early as February, but more usually they fly later in spring.

More info at: UK Safari Leaf Miners Fact File

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