What do knoppers, spangles and apples have in common? No, its not a game or a trick question! The're types of “galls” that can grow on oak trees and autumn can be a good time to look for some.
Galls form when a plant grows differently in response to the presence of a parasite for example when an insect lays eggs within a plant, or a fungus finds its way in. As far as is known galls don't harm the “host” plant but can take some weird and wonderful shapes. Country names were often adopted for the more common ones such as witches brooms (that look like tight bunches of twigs) on birch trees – caused by a fungi, and robin's pin cushion (a round growth covered in long hairlike strands) on wild roses – caused by a wasp.
Back to knoppers, spangles and apples on oak trees – these are also caused by gall wasps! Not those wasps that might sting you but rather smaller insects only a few millimetres long! 42 types of gall wasps use various parts of oaks (catkins, buds, acorns, leaves, roots) to breed in. As well as knoppers, spangles and apples, there are currants, hedgehogs, artichokes and marble galls that occur on oaks! Each gall type contains a different stage of life of either one, or several gall wasps.
As autumn advances spangles form on the underside of oak leaves, and knoppers on the acorns of Turkey oaks! As winter takes hold the knoppers turn brown and drop to the ground.
Please let me know if you find any.
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