Gall Wasps

                       Cherry Oak Gall caused by Cynips Quercusfolii

Mutant acorns, or knopper galls, are a familiar sight to many of us. Many may also be aware that they are caused by a gall wasp. there could be as many as 80 species of insects that induce galls on our native English and Sessile Oaks.

Knopper Galls caused by Andricus quercuscalisis

Galls are abnormal growths in the host plant and are characteristic to each specific gall-maker. The abnormal growth is induced when the egg hatches and the larva uses the gall as it grows for protection and food. It all happens as part of a natural cycle and has no impact on a healthy tree. 

Smooth Spangle Galls caused by Neuroterus albipes

Galls can be caused on the flower buds, leaves, twigs, trunk, roots or on the acorns themselves. The oaks of Bicknor Wood play host to a number of species.

Common Spangle Gall caused by Neuroterus quercusbaccarum

Not all larvae found in the galls are from the original egg-layer (causer) however. Other insects (inquiline) lay their eggs in galls and their larvae compete with the incumbents for the food provided by the growths. Others still (parasitoid), lay an egg on, or even in, the resident larva with the intention that their progeny will kill and consume the original inhabitant, all the while benefitting from the protection of the gall.

Whichever one of these characters you may have your money on, they emerge as adults and different insects then make use of the hollowed out galls as shelter. 

Many of these fascinating creatures have two generations per year that alternate between sexual and asexual (cyclical parthenogenisis). The sexual generation consists of both genders and reproduces in the expected manner, but the eggs lain will all prove to be female and hatch as the asexual generation. Each generation induces a different gall and will sometimes use a different host tree species. 

Yet to be specifically identified

Finding the galls allows us to assume a presence of the creatures in the wood and they can therefore be added to the list of life that exists within it. 

The invasive Oriental Chestnut Gall Wasp, Dryocosmus kuriphilus, has found its way to Bicknor Wood from Asia, via Farningham Woods (M25 J3). It is a Sweet Chestnut specialist and a kinked curl at the edge of a leaf is the first sign that a gall has been induced.