The word knopper derives from the German word Knoppe, meaning a kind of felt cap or helmet worn during the 17th century.
On my walks I have been picking up a few misshapen acorns, less this year than I remember from previous years. They always make me think of the animated film Epic (2013) when the good and bad battle it out in the faery realm, helped by a human teenager who has been magically miniaturised.
I was intrigued as to what caused this, as they give off a strong life, very feminine energy. The picture below shows the culprit who made the one in my picture, Andricus quercuscalicis!
Knopper galls develop as a chemically induced distortion of growing acorns, caused by gall wasps, which lay eggs in buds with their ovipositor. An ovipositor consists of a maximum of three pairs of appendages, its form is adapted to functions such as transmitting the egg, preparing a place for it, and placing it properly. The gall produced may reduce the reproductive ability of the tree. The knopper is a recent introduction to the British Isles, first arriving in the 1960s and now found throughout England, Wales and Scotland.
The 2 cm gall growth looks a mass of green to yellowish-green, ridged, and to begin with, sticky plant tissue, that breaks out as the gall between the cup and the acorn. If only a few grubs are developing within, then it may appear only as a group of flat folds. Where several grubs are struggling for space, the shape may become much more distorted, with several tightly bunched galls.
Andricus quercuscalicis is a small gall wasp with a two-phase life-cycle that requires both pedunculate oak and Turkey oak. This species has alternate sexual and parthenogenetic (all female) generations.
The abnormal acorns develop during summer and the acorn is either wholly or partially replaced by the gall growth. The knoppers become woody and brown in early autumn, after which they fall from the tree and the adult sexual female gall wasp emerges through a vent in the top of the gall in spring. The level of attack by the insect varies from year to year.
The fact that the specimens I have collected contain a potential female wasp explains my feeling of strong feminine energy. The powerful life force I assume is due to the combination of the actual acorn, together with the growing parasites, competing for who will survive.
This is a different knopper I found on another walk, made by a different wasp, the Oak marble gall wasp (Andricus kollari).