The life history and case-building behavior of Molanna tryphena Betten from 2 spring-fed tributaries in east Texas were studied from January 1997 to May 1998. The 344 larvae, pupae, and adults sampled indicated a univoltine life cycle, with an extended adult emergence period. Fecundity was 76.2 ± 9.7 eggs per female. Larvae were recruited in spring and summer, and grew to late instars or pupae by fall. Larvae and pupae were found mainly in the sand substrate. Eggs, larvae of 2nd and 5th instars, pupae, cases, and adults are described. Case reconstruction behavior was observed and videotaped. Larvae constructed emergency cases by gluing together sand and burrowing inside to form a tube. Sand and gravel were added over the next 12 h to strengthen the tube and add the cowl and flange typical of Molannidae.