There’s now a third species of gall to look out for on Walnut trees. More...

Walnuts are not native to the UK but, as attractive and productive trees, they are often planted in parks and gardens.  Various gall mites in the genus Aceria provoke the leaves to form distinctive structures, which provide a home where the mites can develop. Aceria erinea creates obvious concave bulges up to about 2cm across that you can find on almost every walnut tree. Aceria tristriata is less common but has still been recorded from a dozen sites in Leicestershire & Rutland.  It causes the leaves to become dotted with small, hard blisters, which are concentrated along the veins.
For its Members’ outing in June, the Natural History Section of Leicester Lit & Phil visited the Wash Brook Nature Reserve in West Knighton and discovered Aceria brachytarsus alongside the other two species.  These galls are 3-4mm across and project from both sides of the leaf, being roughly hemispherical above and conical below. The species was first found in the UK in 2021 and there have been records from London, Cambridge and Norfolk since then but Leicester appears to be the furthest north and west it has been recorded so far. Was this sighting a one-off or is the species now becoming common across our two counties? Do check any walnut trees in your neighbourhood and log the results on NatureSpot so we can build up a picture of its distribution!