Deoptilia heptadeta is a moth of the Gracillariidae family. It is known from Japan (the Ryukyu Islands, Kyūshū, Shikoku, Honshū, Tusima, the Amami Islands) and Taiwan. The wingspan is 6.3-8.3 mm. The larvae feed on Mallotus japonicus. They mine the leaves of their host plant. The mine usually occurs upon the upper surface of the leaf; at first it is an entirely epidermal and linear gallery, whitish with a glassy luster and irregularly curved, sometimes occurring along the leaf-veins. Soon after, it is broadened into a moderate blotch, sometimes elongated along a leaf-vein or situated on a space between two veins. It is whitish and blister-like. In the later stages the larva continues feeding on the leaf-tissue within the blotchy mine. Finally, it leaves only upper and lower epidermal layer