27th May 2014

Galls have several causes- viruses, fungi, bacteria and insects, and appear on half of all plant species. In all cases, the host plant is invaded which causes the host plant to reorganise its cellular structure to provide nutrition, protection and/or shelter for the invading organism, in a parasitic relationship. Oak Apples, produced by Gall Wasps or Cynipids, are perhaps the best known galls, but a single Oak Tree, like the one we are lucky to have at the end of our garden, may support thousands of galls of different sorts without causing real damage to the tree. Over the last few weeks hundreds of these small Currant Galls have been appearing on the tree, with many falling onto the ground. The Gall Wasps that cause these Currant Galls to grow have a fascinating life-cycle. In autumn, eggs are laid on the backs of oak leaves causing Spangle Galls, which all hatch into female wasps. These are agamic, meaning they can reproduce without mating. In spring it is these which lay eggs in oak buds and catkins, generating Currant Galls, which hatch as males and females in June, mate and lay the eggs that form the Spangle Galls, and so it goes on. Gall Wasps not only cause the plant material to change form but cause the oak tree to produce more nutrients in the gall cells, to feed the larvae which hatch inside the gall. The larvae have  sealed guts until just before they hatch, so they don’t foul their home! Even these little galls have been shown to creat mini-ecosystems for other lodgers, and they can themselves be parasitised by parsitoid wasps! More of galls another time I’m sure! Conditions: A dull, quiet, cloudy day, occasional very light rain. Temperature: Max 14- Min 10 c

Closeup of the Currant Galls.

Close-up of the Currant Galls.


Currant Galls growing on our Oak tree

Currant Galls growing on our Oak tree

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