Thursday, 14 February 2013

Conker Trees

The Horse Chestnut, Aesculus hippocastanum, seems to have arrived in Britain around 1610. It is native to the Balkans and Greece but is generally pretty hardy in I can never recall having seen a tree frost damaged. True chestnuts belong to the very large Oak family, Fagaceae, but Horse Chestnuts are not at all related and are placed in a far smaller family, the Hippocastanaceae. A Sweet Chestnut is a fruit whereas a conker is just a seed.

I suppose that, like many children, the Horse Chestnut was one of the first trees I learnt to recognise, obviously because its large round seeds were used for playing conkers but also through its panicles of cream and pink flowers, which we called "candles". I had always assumed that the word "conker" derived from "conqueror", since the object of the game is to conquer your opponent's specimen. However, I find that on old version of the game was played with snail shells and the alternative possibility is that "conker" is from the French word "conque" - a shell. We may never know the truth. 

I have spoken of the seeds but not their protective spiny casing. Nor have I mentioned the distinctive leaves with their palmately compound arrangement of leaflets. In recent years the leaves have become disfigured by larvae of the Horse Chestnut Leaf Miner as shown in the picture. This moth, Cameraria ohridella, seems to have arrived in Britain in 2002 but has spread at an astonishing rate, affecting all the trees I've seen in the last two or three years.

Damage by the Horse Chestnut Leaf Miner,
Byfield Pocket Park, Summer, 2012
Despite being so unsightly there seems to be no long-term damage to the trees. What is surprising, for a moth which arrived so recently, is that a number of parasitoid wasps have already begun to take advantage of this newcomer. These wasps attack the almost full-grown larvae by laying eggs on them. When an egg hatches the wasp grub enter the body of the larva and feeds on it though, surprisingly, less than 10% of the victims die as a result. (British Wildlife, Vol 22, No 4, pages 305-313).

The conkers are poisonous although cases but on the other hand I was told as a child that they could be used to make soap. This is true. The conkers contain saponins and these are the active ingredient in many soaps now available commercially although I have no plans to purchase them - or make the soap myself.

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