Pyraloid moths in the subfamily Acentropinae have developmental stages that are aquatic, they live and breathe underwater during all or part of their life cycle. We discovered and describe the previously unknown larvae of Usingeriessa onyxalis (Hampson) (Crambidae) reared on Hygrophila polysperma (Roxb.) T. Anderson (Acanthaceae) and Eleocharis sp. (Cyperaceae) in Texas.We also describe Oxyelophila callista (Forbes) feeding on at least five species of aquatic plants in Texas. Morphological and molecular characters were used to associate immatures with adults. These are the first accounts of the immature stages of U. onyxalis and the first detailed description of the immatures of O. callista, so we discuss the current classification and generic placement of these and associated species. Images and line drawings of the aquatic larvae, adults, and male and female genitalia of U. onyxalis are provided, as well as a table comparing the larval habit and morphology among genera. The current process of boiling larvae for preservation as voucher specimens and morphological study is discussed in light of current molecular techniques.