Margarinotus ephemeralis is a species of clown beetle in the family Histeridae.

[1][3][4] The body is oblong oval and measures 3.8–5.2 mm (0.1–0.2 in) in length (from anterior margin of pronotum to posterior margin of elytra) and 2.7–3.2 mm (0.1–0.1 in) in width.

The prothorax has convergent, arcuate sides; the pronotum has a single lateral stria.

[1] Some specimens were collected from the burrow entrances of California ground squirrel, and others from temporary pools where they presumably had been flooded out of burrows.

This species might be an obligate inquiline of California ground squirrel burrows.