Mecodema aberrans is a medium-sized (14.6–19.5 mm length, 5.3–6.5 mm width) ground beetle endemic to the South Island, New Zealand. This species is within the curvidens group[1] and is one of three species that is a braided-river ecotype. It occurs in Otago and Canterbury.[2]
The body colour of the species varies from black (dorsal) to brown (ventral), legs may be a red-brown. To reduce the abrasion of the ventral abdomen, ventrites 3–5 are covered in a large number of setae, which is one of the distinguishing features of this species. To further identify M. aberrans from other Mecodema species there is a difference in the size of the asetose punctures along elytral striae 9 in comparison to striae 1.