The Acorn Gall wasp, Andricus quercuscalicis, causes these strange Knopper Galls on Oak acorns. The wasp oviposits its eggs in the acorn in early Summer as the acorn starts to develop. The egg hatches into a grub which then secretes chemicals causing a gall to form. The grub pupates inside the gall and emerges in the following year.
The wasp has a two generations per year and requires both native Pedunculate( English Oak) Quercus robur or sometimes in Sessile oak, Q.petraea, and, Turkey Oak Q. cerris . The first generation of adult wasps to emerge in spring are all female, they lay their eggs in the young oak buds. The second generation of the life cycle sees sexually reproducing male and female wasps emerge from the galls, the female returns to lay eggs on the English Oak and the cycle begins again. The Acorn Gall wasp has only been known to be in Britain since the 1950's, having made its way north from Europe. The introduction of the Turkey Oak to Britain in the 1700's eventually facilitated the arrival of the wasp from Europe.
|Plenty of things to paint at this time of year!|
Colours: Lower acorn, Gold Ochre and Burnt Sienna, built up in washes with a wash of Transparent Yellow applied on top. Highlights were left clear and a small amount of Cerulean Blue used to bring the highlight forward. A little dry brush work was used the build up the rich colour on the acorn. Acorn 'cap', Green gold, Indanthrene Blue and some Burnt Sienna on top for the indents.
Gall, Burnt Sienna and Raw Umber with Ultraviolet and Indanth Blue for the shadows.