Megachile (Addendella) are robust bees with black integument. They have primarily white hair on their body with some black hair on the head, scutum, scutellum, the discs of the terga, and S6 (Mitchell 1935b). Their body length ranges from 10–17 mm (Mitchell 1935b, Michener 2007). Megachile (Addendella) are univoltine, and adults have been observed flying from May to early July (Mitchell 1935b). This subgenus was previously synonymized with Megachile (Xanthosarus), but was revived by Gonzalez et al. 2019.
Megachile (Addendella) females can be confused with Megachile (Litomegachile) because of their similar four-toothed mandibles and concave T6 when viewed in profile. M. (Addendella) can be distinguished by their larger size and denticulate clypeal margin (Mitchell 1935b; Michener 2007). Male M. (Addendella) can look similar to Megachile (Argyropile) parallela in the wide emargination of the T6 preapical carina and the four-toothed mandibles. M. (Addendella) differ in their dense patch of red bristles at the base of the front coxa and the absence of sublateral spines on the apical margin of T6 (Mitchell 1935b).
Megachile (Addendella) have been observed visiting the flowers of multiple plant families including Cactaceae, Ericaceae, Fabaceae, Hypericaceae, Onagraceae, and Plantaginaceae (Mitchell 1935b). They have also been shown to be effective pollinators of commercial cranberry (Cane et al. 1996). Females have been found cutting maple leaves (Acer rubrum) to line their nest cells, and males have been observed patrolling maple trees (Cane et al. 1996).
Megachile (Addendella) nest in the ground where they excavate their own nest cavity in the soil (Cane et al. 1996). The nests are usually shallow (4–17 cm) with a short main tunnel ending in horizontally arranged cells. Nest cells are lined with cut leaves and usually arranged singly or in groups of two, although they have sometimes been found arranged linearly, with 4–9 cells per nest (Cane et al. 1996).
Megachile (Addendella) includes a single species, Megachile addenda (Gonzalez et al. 2019).
There are no known invasives.
Megachile (Addendella) are known primarily from the eastern U.S. from southeastern Canada south to Florida (Mitchell 1935). They have been reported in the southern part ofthe U.S. as far west as California,but are mostly found east of Kansas (Mitchell 1935).