These almost microscopic, pale yellow sap-sucking insects, related to aphids, feed on the roots and leaves of grapevines (depending on the phylloxera genetic strain). On "Vitis vinifera", the resulting deformations on roots ("nodosities" and "tuberosities") and secondary fungal infections can girdle roots, gradually cutting off the flow of nutrients and water to the vine. Nymphs also form protective galls on the undersides of grapevine leaves of some "Vitis" species and overwinter under the bark or on the vine roots; these leaf galls are typically only found on the leaves of American vines.