Oak apple and Currant galls

This oak, just coming into leaf beside the river Tyne at Wylam yesterday, was carrying both oak apple galls and currant galls.

The big, spongy oak apple is caused by the tiny wasp Biorhiza pallida, which lays its eggs as the base of an oak bud and causes it to swell into this large gall that's home to up to 30 of the gall wasp's grubs. After it matures in July the hatching adults chew their way out, leaving distinctive exit holes. 



Oak apples contain either all male or all female wasps but when they emerge they mate and the fertilised females then lay their eggs on the oak's rootlets, when they form a much smaller woody gall. Only females emerge from these and in late winter climb the oak's trunk and lay eggs to form the next generation oak apples.

The small red, spherical galls dangling under the oak apple are currant galls formed in the catkin of the oak, when the gall wasp Neuroterus quercus-baccarum lays its eggs in the male flowers. Each currant gall contains a single grub  and either males or females hatch in June. After mating the female lays her eggs on the underside of the oak leaves, where they form the familiar spangle galls that cover the lower surface of the leaf in autumn.



Spangle galls drop off shortly before the leaves fall in autumn, then in spring females emerge and lay eggs in the oak's catkins, producing currant galls again.

For more pictures of plant galls click here

Plant galls

This is probably the best time of year for anyone interested in plant galls - those strange growths on plants caused by insects, mites and sometimes fungi. These are a few that I've seen locally over the last couple of weeks.

Leaf petiole of common lime Tilia x europaea with a gall chamber containing larvae of the gall midge Continaria tiliarum.

Ash flowers galled by the ash gall mite Eriophyes fraxinivorus.

An old oak apple gall caused by the gall wasp Biorhiza pallida, with exit holes where the adults have hatched.

Silk button galls on the underside of oak leaves, containing larvae of the gall wasp Neuroterus numismalis

Spangle galls on the underside of an oak leaf, containing larvae of the gall wasp Neuroterus quercus-baccarum.

Galls on leaf surface of sycamore caused by the eriophyid mite Eriophyes macrorhynchus aceribus. Click here for pictures of eriophyid mites.

Bean gall in the leaf blade of willow, containing the larva of the sawfly Pontania proxima

Robin's pin cushion or bedeguar gall on wild rose, caused by the gall wasp Diplolepis rosae. 

For pictures of the gall wasp click here. 

For pictures of the parasite that attacks the wasp, click here.