Plant galls are abnormal growths that have formed as a reaction to species such as wasps, mites, or flies laying their eggs in different plant hosts and some are also caused by fungi and bacteria. Plant galls are some of the most fascinating natural structures with 2000 different galls present in the UK. Come the summer, it’s great fun going on a hunt to find them and it’s one of my favourite activities to do in the parks and green spaces in Ipswich. One of the best things about galls is that often the gall-inducing species has two generations emerging at two different times of year, producing two completely different types of gall types and shapes and further opportunities to see these wonderful natural structures.

In the summer, great galls to look out for are the blistered bumps that the walnut gall mite, Eriophyes erineus, produce, sometimes completely covering walnut tree leaves, making themselves at home as soon as a leaf unfurls. Great places to find these in Ipswich are in Chantry Park, the largest of all the town’s parks.

Along the streams running through Purdis Heath are several alder trees, and sat on top of the leaves in the summer you can find a variety of different galls created by a variety of species that choose alder to lay their eggs in.

Last week I spotted galls on alder leaves that I think look a little like popping candy, but are sure to not taste similar, created by the mite Eriophyes laevis. Being green at first then turning pinky red later in the year, the mites emerge in the autumn spending the winter in cones and tree crevices. Alders are water-loving trees, and plenty grow near the ponds and waterways in our green spaces in Ipswich. Head towards water to find these trees and their gall decorated leaves. 

Providing completely different shapes, and probably some of my favourites, are those that can be found on oak trees. Artichoke galls, caused by the wasp Andricus foecundatrix can be seen from mid-summer and mature in August where the inner gall is forced out, falling to the ground. The single larvae that is housed inside will pupate in the fallen gall, emerging next spring. 

Ramshorn galls, caused by the wasp Andricus aries, are elongated with a rounded base and yellow / green in colour that turns brown as the gall matures in the autumn and can last on the tree for years, long after the young inside have emerged. There can be some variation in shape with these galls with some looking as described, like ram's horns, and others are much longer without a pronounced horn-like curve just tapering out at the end.

You can see the variation of ramshorn galls in the photos below from Bourne Park. If you are looking out for galls for the first time, Bourne Park is a brilliant place to start in Ipswich as the young oak trees provide a great opportunity to check the whole tree over, whilst the more mature oaks give those feeling more adventurous an opportunity to climb them and a harder, but fun, challenge to spot galls.  

Providing a different shape completely, oak marble galls are caused by the wasp Andricus kollari, and sit rotund on branches. Not being native to the UK, it is thought that this solitary wasp was initially introduced in the UK as a source for tannin for dyeing and ink making industries.

Look out for green marble-like balls on branches in the summer but also keep your eyes peeled in the autumn and winter for this gall when it turns brown and lasts on the branches throughout the winter. These galls are on Rushmere Heath, where the young sapling oak trees provide great accessibility.

Often more noticeable in their golden brown 'autumn colours' I spotted the early stages of the spangle gall this week on the underside of oak leaves, where the gall wasp Neuroterus quercusbaccarum has laid its eggs, causing spangles with tufts of red hair to form. Each spangle houses a single larva and they fall to ground in the autumn where they then spend the winter maturing until they are ready to emerge in the spring.

I found these in Christchurch Park so why not go there yourself and inspect the underside of some oak leaves or look out for them in the autumn.

Last, but by no means least, is the knopper gall created by the wasp species Andricus quercuscalicis that can be found on acorns on oak trees. Identified by being green and knobbly all over with an uneven surface in the summer, this gall has a small hole which leads to a chamber with the larvae inside. Turning brown as they mature, the galls fall to the ground and whilst they normally emerge as adults the following year, they can remain inside for as long as four years! 

In most cases, galls are only a cosmetic complaint rather than causing lasting damage to their hosts, and as the empty galls often stay on the branches after their inhabitants have emerged, and in some cases for a couple of years afterwards, they provide lots of opportunity throughout the year to search for them.

Why not go on a gall hunt yourself using our gall spotter sheet and see how many you can find?