Galls

A gall is a specific part of a plant that has been changed by another organism. The organisms can be animal or plant. The host plant does not benefit from the relationship but rarely will they die.

The gall is formed when the gall forming organism introduces sustances that affects the host plant's growth pattern. The growth pattern becomes adapted to the needs of the gall forming organism, not only creating these wonderfully unusual shaped galls but sheltered havens and food source. The final gall shape will depend on the species of gall forming organism, of which there are many.

Galls are relatively common however they are not often noticed and because of this only a few have evolved common names. Many abundant species are only known by their scientific name.

Marble Galls

Round marble size galls are to be found on oak trees. The galls are at first green in summer but later ripen to brown. The galls do not fall off in winter and are easy to spot on bare trees.

The gall is the product of a small gall wasp Andricus kollari.

Observing a brown gall in winter, one can see the wasp's exit hole.

Oak Spangle Gall

The small gall wasp Neuroterus quercusbaccarum produces two types of galls on oaks. In autumn flat spangle galls form on the back of leaves, the leaves fall and females emerge next spring.

These females lay eggs on the male catkin buds, forming small round galls.

From these galls both male and female wasps emerge in summer. This generation produces eggs which are laid on the back of leaves, restarting the cycle.

Bedeguar Gall or Robin’s Pincushion Diplolepis rosae

Bedeguar galls are formed on the wild rose by larvae of the gall-wasp Diplolepis rosae. A bedeguar gall is not the product of a single larva but a group of larvae, each residing in their own chamber within the gall.

Other species of wasp larvae will also make use of the gall. There are the species that do not form their own galls but just utilize those already formed by others, these are inquilines. The major inquiline is Periclistus brandtii, this has a commensal relationship, i.e. it benefits from the arrangement, but does not have a detrimental affect on Diplolepis rosae.

More incidious is the possible introduction into the gall of parasitic wasp larvae that will gradually consume Diplolepis rosae.

Diplolepis rosae over winters in the gall emerging as adult wasps in spring. The adult wasps reproduce not needing males i.e. parthenogenetically.

Thanks to Steve for additional information

Photograph by Steve Clemens 

Sputnik Gall on Rose Caused By The Gall Wasp Diplolepis nervosa