Saturday, 1 November 2014

Leaf mines on hogweed

Although it's very common at Filnore Woods, Hogweed is very obliging in that it provides flowers pretty well all year round.  Even today it is still producing new buds for the next bunch of flowers. 
It will grow in long grass, amongst nettles, on the edge of the woodland, in hedgerows,
anywhere where it can get enough light.

The flowers can be creamy white or tinged pink.  They are arranged with the longest petals on the outside of each circular flower cluster with about a dozen clusters
in each big umbel, like a sort of firework going off.
Today I noticed some strange, white markings on some of the hogweed leaves. 

A closer look revealed a tangle of little, white lines
snaking all over the leaves
Each thread is the tunnel left by the larva of a tiny fly.  The larva (or grub) eats away the green cells of the leaf as it crawls along, without damaging the upper or lower membrane of the leaf.  As the grub gets fatter the tunnel gets wider and you can see this when you look closely. 

  Eventually it is ready to pupate and drops out of the leaf to become an adult fly in its turn, and repeat the cycle.

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