A gall is an abnormal plant growth caused by various parasites such as fungi, bacteria, insects or mites. The plant cells swell and change in size in order to house the parasite inside. The parasite receives shelter and food inside the gall and is provided with a safe environment for its young.
 Alan Stubbs.JPG) |
| A miniature fire gall by a tiny gall wasp (Diplolepis mayri) © Alan Stubbs |
Britain has hundreds of different types of gall, each plant or tree species having its own ‘art’ forms according to the invertebrate which caused it. For the most part galls are much easier to observe and identify than the invertebrates found inside them.
Many galls can be caused by insects called Gall wasps. Gall wasps are in the order Hymenoptera (bees, wasps and ants) and Cynipidae family. They are either parasites of plants or parasites of their fellow parasitic wasps (called hyper-parasatoids). The majority of wasp galls can be found on oak trees.
The gall develops after the female has deposited the eggs into the plant. Scientists still do not know exactly what triggers the growth of the plant gall. The hatching young feed on the plant in the safe environment provided by the gall. The host plant species, size, shape and colour of the plant gall indicate which parasite is inside.
One of the common wasp galls is the Robin’s pin cushion gall found on Field Rose (Rosa arvensis) or Dog rose (Rosa canina). This gall is caused by Diplolepis rosae.
To find out more about plant galls visit the British Plant Gall Society by clicking here. A comprehensive, gall identification guide is published by the Field Studies Council.
