The European Cauliflower Gall 22.10.25
Holt Island has a number of Ash trees on it; the trees have large bunches of Ash keys. But if one looks closely there are a number of brown lumps in with the Ash keys. These are European Cauliflower Ash Galls. They are formed by the gall mites Aceria fraxinivora. The galls are formed in the flower clusters; the eggs of the mites being laid soon after they open. As the mites are mainly female, the eggs do not need fertilizing.
The mites are very small, around 0.5mm long cylinders. Scanning electron microscopy images can be seen here. They can pierce individual plant cells, on which they feed. The surrounding cells enlarge and multiply and this forms the gall, which can be 2 cm long, they will turn brown and black and will stay on the tree for up to two years.
The gall mites are members of the spider family, Arachnida. They are very specialised and only reproduce on Ash tree species. They are sap eaters; they have no circulation or respiratory systems. They have two pairs of legs and no eyes, so a rather curious creature.
This year there are a lot of galls in amongst the Ash keys which can easily be seen on the Island. Next year a large number of mites will emerge from each gall. They are widespread in Britain, wherever Ash trees are present, but particularly in Leicestershire and Rutland.
Left: Cauliflower Ash Galls. Below: close up of an individual gall
Photos: Julian Limentani
