Both Linderomyia fergusoni and L. denticulata have the wing costa nearly straight as it approaches the end of vein Sc, and wing cell c is either equal to or less in length (as measured from the humeral vein to Sc) to cell sc. L. austraquila also occurs in Tasmania and is somewhat similar looking to these two species but has the wing costa noticeably arched as it approaches Sc (similar to L. flavipalpis) and cell c is slightly longer in length to cell sc.
Male L. fergusoni have deep black bodies with antennae, palps, and halteres brown. The abdomen is marked dorsally with grey dusting as follows: thin hind margin of tergite 1; a narrow lateral basal mark may or may not be present on tergite 3; a narrow lateral basal mark on tergites 4-5; tergite 6 almost entirely. Male L. denticulata differ by lacking any dorsal grey marks on tergites 1-5.
Female L. fergusoni are lighter than their male counterparts, the thorax being brownish grey dusted with vague vitta, and the abdomen more extensively marked dorsally with grey (sometimes bluish depending on angle) as follows: tergite 1 entirely excepting the base; tergite 2 laterally in the basal half (sometimes meeting in the middle); tergite 3-4 laterally in the basal half (more or less); tergite 5 variably from only a narrow lateral basal mark to almost entire tergite (excepting narrowly apically); entirely tergite 6. Female L. fergusoni lack thoracic vitta and the abdomen is less extensively marked dorsally grey, with tergite 5 notably lacking any such grey markings.