The nail galls on linden leaves induced by Phytoptus tiliae are a familiar and striking foliage injury. They are usually numerous and are scattered at random over the leaf surface, generally missing the veins. Each gall is an elongate structure, attenuate distally, with a rounded or pointed tip, measuring 5-12 mm long, which may be erect, oblique, or curved, pro truding through the upper surface of the leaf blade. Some times two galls are coalesced at the base but form separate apices. The interior of the gall is filled with long, simple hairs near the base or opening (see pi. 6, D). The galls vary from greenish yellow to pinkish, to red and brown. They appear in June, maturing in July-August.

Although a common species, nothing is known of its life history. It is one of the many eriophyids that attack the linden family Tiliaceae and cause galls to form. Phytoptus tiliae is apparently widely distributed.

- Hartford Keifer,Edward Baker,Tokuwo Kono,Mercedes Delfinado,William Styer: (1982) An Illustrated Guide to Plant Abnormalities Caused by Eriophyid Mites in North America^©

Reference: https://babel.hathitrust.org/cgi/pt?id=uiug.30112019256624&view=1up&seq=72