Mordellistena y-nigrum is a species of beetle in the family Mordellidae.

It was described in 1937 by Eugene Ray from Puerto Rico.

[1][2] It is named for its diagnostic characteristic, a Y-shaped black spot on the region of the elytra surrounding the scutellum.

[1] This beetle measures 2.25 mm (0.089 in) in length, or 3.1 mm (0.12 in) when including the anal stylus.

The antennae are 1 mm (0.039 in) long.