Wednesday, 4 September 2013

Oak galls

Last year we had a load of oak apples at Filnore, which are a type of gall.
Taken May 2012
But in 2013 I haven't seen any.

 On the other hand we have a lot of Knopper Galls this year, forming on some of the acorns. 



They are the result of an attack by a tiny little gall wasp Andricus quercuscalicisThe insects that emerge from these in spring will be only females.  
photo by Paisley Natural history society
They then fly off to find a Turkey Oak tree and lay their eggs on the catkins causing small conical galls to grow.  From these galls, in May or June, emerge a bisexual generation - males and females.  It is their grubs that cause the knopper galls on common oak.  Round and round it goes.

Spangle galls on oak leaves also produce female gall wasps only.  This time called Neuroterus quercusbaccarum.  The galls fall to earth in the autumn with the leaves and in spring the female gall wasps emerge and fly to lay eggs in oak buds.  The resulting currant galls give rise to a male and female generation.  After mating, the females lay their eggs, in summer, on the leaves of the oak and new spangle galls are created.  
All the photographs of spangle and knopper galls were taken in the western corner of Filnore Woods, near post 2 (which is actually a number 2 painted on a cherry tree).  You can see that some of the oak leaves are covered in galls, though it doesn't seem to do the trees any harm.  It's a bit like spots and pimples on us.
So a good year for spangle galls and knopper galls if not for oak apples.

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