Until the description of Grahamstoneia humboldti in 2021, galls now known to belong to that species were typically identified as Andricus projectus. The species can be distinguished by the following traits.

A projectus galls first appear in the spring on overwintered flower and leaf buds and are tan-pink even early in their development. They have a plump, rounded shape and are hairless with the exception of a typical but not universal tuft of hairs at the tip resembling those found on bud scales. They are slightly narrowed and lighter in color at the tip but lack a distinct pointed tip. The galls persist on the tree into the summer and overlap with the beginning of the season of G humboldti, but are typically visibly weathered and never green. According to Weld, the galls drop in November. Adults emerge in the following spring or in the spring up to 6 years later.

G humboldti galls have been seen as early as July 31 but are typically not seen until later in the fall. They are slender, pointed, and green or brown, sometimes with a uniform coat of loose hairs. They always have a distinct "torpedo" tip, with distinct coloration (lighter green than the base or light brown). The wasps apparently emerge in November in the same season the galls developed.

Given the fact that Weld named A projectus the "torpedo" gall after a trait obvious in G humboldti and absent in A projectus, it seems possible that he mistook the galls for a single species. Traits given in his description of A projectus may plausibly refer to either species, so caution should be used in relying on them.

No good cross section of G humboldti is available, but the two species likely differ in internal structure as well. The internal structure of A projectus doesn't match the drawing provided by Weld (Figure 161), suggesting that Weld's drawing may represent G humboldti instead.