The greenhouse millipede (Oxidus gracilis), also known as the hothouse millipede, short-flange millipede, or garden millipede, is a species of millipede in the family Paradoxosomatidae that has been widely introduced around the world, and is sometimes a pest in greenhouses.

Greenhouse millipedes achieve lengths of 18 to 23 mm as adults, and widths from 2 to 2.5 mm. The dorsal section of each segment has a transverse groove, a trait found in most paradoxosomatids. They are brown in color with pale cream-colored legs and paranota (lateral "keels" extending from each segment).

Greenhouse millipedes are thought to be native to Japan, but have been introduced globally. They are found in the tropics as well as temperate North and South America, and all of Europe.