Aceria macrorhyncha

Gall mites are extremely tiny plant feeders, often around 0.5mm in size. They are members of the Arachnid group, which includes spiders and mites, and are small enough to pierce and feed on individual plant cells, causing the surrounding cells to enlarge and multiply to form the gall. The mites are sap-sucking elongated cylinders, which apparently have no eyes, circulation or respiratory system and just two pairs of legs. Aceria macrorhynchus produces a red pustule gall on the upper surface of the leaves of Sycamore. The galls are far easier to see than the mite.

Aceria cephalonea

Adult Gall

Only on Sycamore.  Aceria macrorhyncha galls are up to 6mm long, with a pointed tip.  Aceria cephalonea galls are smaller and shorter (less than 3mm) and have a rounded tip. Intermediates do occur, and these can't be identified from the galls.  

Some indication of the size of the gall is helpful, and a close-up photo.  The host plant must be specified in the comments box - e.g. "Galls on Sycamore, 5-6mm high"

Wherever Sycamore is found.

Summer and Autumn.

They are mainly all female, producing eggs which need no fertilization.

Quite common and widespread in Britain.

Fairly common in Leicestershire and Rutland.