The objective of this research was to describe the anal plates of the larval stages of the ephydrid fly, Hydrellia pakistanae Deonier, a biological control agent of hydrilla (Hydrilla verticillata (L.f.) Royle). This was accomplished using light microscopy coupled with a specialized staining technique; and scanning electron microscopy (SEM). AU 3 instars of H. pakistanae were collected from hydrilla cultured in outdoor concrete-lined ponds. To ascribe a function to the anal plates, a modified staining technique was employed that uses a 5% silver nitrate solution, which, upon ionization, binds with chloride ions suggesting an osmoregulatory function. Under light microscopy the two anal plates appeared smooth, flat crescent moon-shaped structures that encircled the anus of the larva. SEM revealed the anal plates to be relatively smooth with an undulating surface pattern possibly an artifact of the high vacuum conditions associated with the SEM. This may therefore indicate a difference in cuticle thickness for the anal plates since the overall body cuticle did not exhibit the same surface changes. A distinct delineation in the form of a thin raised line of cuticle between the anal plates and the outer body cuticle could be discerned from both light microscopy and SEM. The anal plates vary in size from 200 µm to 750 µm in perimeter and 1800 µm² to 14000 µm² in area depending on instar. A highly positive correlation in anal plate size in relation to larval instar was also detected; i.e., larger anal plates were associated with later instars. The anal plates darkened rapidly after immersion in a weak silver nitrate solution with subsequent exposure to light indicating that they may play an important role in maintaining internal ionic equilibrium.