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One of the bigger Acleris species, with a wingspan of 12.5-16.5 mm, hardly distinguishable from A. stadiana. Ground colored forewing with a costal triangle, including a costal margin. Within the costal triangle, cinnamon drab to fuscous with brownish highlights. The basal patch is sometimes defined by a small and thin transverse line. The coloration of the hindwings is similar to that of the forewings. Unlike A. stadiana, male A. semiannula have a short, broad and almost straight aedeagus. Females display a broad and flat sterigma, with sharply pointed lateral tips, whereas female A. stadiana also have a broad and flat sterigma but their lateral tips are rounded and blunt (Sabourin et al. 1997).

Larval host records include silver maple (Acer album), red maple (Acer rubrum) and white oak (Quercus alba). The larvae only spare the upper leaf epidermis, when they crumple and skeletonize their hostplant’s leaves from underneath, tying the lobes with silk. For metamorphosis, the larvae build thin cocoons among webbing on the crumpled leaf and right before emerging, the pupae extend from the cocoon (Sabourin et at. 1997). Depending on the locality, adults can be found on wing between March to December (MPG 2019). Some studies indicate that Acleris semiannula is univoltine (Sabourin et at. 1997).

Another Nearctic tortricid, namely Peronea braunana has been generally misidentified as A. semiannula (McDunnough 1997). Furthermore, A. notana and A. ferrugana, which are species native to the palearctic region, are very similar to A. semiannula, which has resulted in various misidentifications and debates about their biology in the past (Sabourin et al. 1977).