The blackline Hawaiian damselfly (Megalagrion nigrohamatum nigrolineatum) is a moderately-sized and delicate subspecies (Polhemus and Asquith 1996, p. 73) found on Oahu. It occurs in the slow sections or pools along mid-reach and headwater sections of perennial upland streams and in seep-fed pools along overflow channels bordering such streams. The adults measure from 1.4 to 1.8 in (35 to 45 mm) in length and have a wingspan of 1.7 to 1.9 in (45 to 50 mm). Naiads remain concealed and are found under stones or in mats of algae e (Williams, 1936, p. 318; Zimmerman, 1948a, pp. 371-372).