At the start of spring, females or stem mothers crawl to witch-hazel leaf buds.

As the leaf grows, the aphid injects it with a substance, possibly an enzyme or hormone, that causes that the galls to form around her.

[4] The first generation of the year is composed entirely of female fundatrices (also called stem mothers), which hatch from winter eggs laid on the bark of witch-hazel.

A gall forms around her approximately 7–14 mm tall on the adaxial (upper) side of the leaf.

The process of “stinging” the leaf to induce gall formation is distinct from normal feeding behavior.

While feeding occurs seemingly haphazardly, a stem mother must repeatedly sting a site over some time to induce gall growth.

[6] When stinging, the aphid repeatedly inserts her stylets into the leaf over a small circular area.

[7] Higher fecundity is linked to larger gall size, as well as increased levels of condensed tannins.