Oak leaf galls

British Science Week 2016 logoAlan Wood

Galls are abnormal growths of various sizes and shapes that can be found on any part of a plant. They can be caused by viruses, bacteria, fungi, nematodes, mites and insects.

Insect galls are formed when the adults or larvae release chemicals into the plants, and the larvae develop inside the gall, which is the insect’s source of nutrients and also provides protection from predators.

Several types of insect galls are found on leaves of oak trees; we often find them during excursions to Wimbledon Common, and they are easy to observe with a stereomicroscope.

Several types of spangle galls (caused by Cynipid wasps) are found on oak leaves.

Oak leaf with galls and minesWhole oak leaf with spangle galls and leaf mines

Galls on oak leafEarly stage common spangle galls on oak leaf; the galls are 1.5 mm in diameter

Common spangle gallsLate stage common spangle galls on oak leaf, caused by Neuroterus quercusbaccarum

Common spangle gallCommon spangle gall

Silk button spangle gallsSilk button spangle galls on oak leaf, caused by Neuroterus numismalis

Silk button spangle gallSilk button spangle gall on oak leaf

Smooth spangle galls on oak leafSmooth spangle galls on oak leaf, caused by Neuroterus albipes

Smooth spangle gallSmooth spangle gall on oak leaf

Spangle galls are not the only sort of galls found on oak leaves:

Pea gallPea gall on oak leaf, caused by Cynips divisa

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