Elachista flammula is a moth of the Elachistidae family that is endemic to the Australian Capital Territory. The wingspan is 9–10.3 millimetres (0.35–0.41 in) for males and 6.9–9.3 millimetres (0.27–0.37 in) for females. The forewings are yellow, powdered with dark brownish grey-tipped scales in males. The hindwings are grey. The larvae feed on Carex polyantha. They mine the leaves of their host plant. The mine is straight and reaches a length of about 150 millimetres (5.9 in). Several larvae may be found on a single leaf. Pupation takes place outside of the mine, along the fold of the leaf.