The winged forms, which are less apt to be seen, are also aphid-like, except that wings are held flat over the back. Neither winged nor wingless forms have cornicles, tail pipe-like structures on the top of the abdomen, as aphids do. The presence of grape phylloxera is best recognized by characteristic galls it produces on the leaves or roots. Root galls are knot-like swellings on the rootlets, and may lead to decay of infested parts. American varieties of grapes, or European grapes on American root stock are tolerant to the root gall form of the insect.
Some varieties are resistant are to root galls, leaf galls or both.
In spring, a female hatches from a fertilized egg that had been laid on the wood of a grape vine. She migrates to a leaf where she produces a gall and grows to maturity in about 15 days. She fills the gall with eggs and dies soon afterward. Nymphs that hatch from these eggs escape from the gall, and wander to new leaves where they in turn produce galls and eggs. There maybe 6 or 7 generations of this form during the summer.