The immatures (larva and pupa) of Rheocricotopus (Psilocricotopus) valgus Chaudhuri & Sinharay are described for the firsttime. The species belongs to chalybeatus group. The larva is opportunistic, present in the fast-flowing streams to slow-flowingorganically enriched sewage drains. It lives in tunnels made of various particles glued together by silky secretions. There are twogenerations a year with peak emergence in April-May and September-November. The sex ratio of females to males is 2:1.