Rates and energies of consumption (C), egestion (F), assimilation (A), respiration (R), growth (Pg), production of exuviae (Pev), and production of egg masses (Pr) and associated efficiencies, and the effects of seasonal temperature, weight and metamorphic stage upon these factors were examined for a typical individual and cohort of Corydalus cornutus (L.) from a stream in North-Central Texas (330 23'N, 97*5'W). Dobson flies are apparently univoltine in the study area, with 11 larval instars. Emergence, oviposition and hatching occur from late May to August. The typical dobson fly hatches in mid-June, grows rapidly until November, and resumes rapid growth in March, reaching full adult size prior to leaving the stream to pupate in early June. Adult females must feed to provide energy to yolk eggs, produce egg-mass coverings and continue somatic maintenance during their week of reproductive endeavors. Metabolic compensation enables larval dobson flies to maintain preferred and fairly constant rates of R during winter (201-451 pl g-1 h~1; 5-15 C) and summer (985-1173 pl g- h1; 20-30 C); with a seasonal acclimatization change point between 15-20 C. Reduction of rates of R through undercompensation during the winter when food is scarce and through partial compensation at high temperatures during the summer conserves energy which is allocated to P, resulting in high ratios of P/R (1.94) and P/A (66%) for the individual larva and, to a lesser degree, for the cohort (P/R = 1.07, P/A = 52.3%, P/B = 9.96). Rates of C, F, A and R, but not assimilation efficiency, were influenced by temperature and size. The energy budget for a typical dobson fly during the 47 wk as a larva was: C = 4167, A = 3442, F = 725, Pg = 2075, Pev = 198, and R = 1169. Ova respired 0.107 cal wk-1, prepupae 357 cal wk~ 1 , male pupae 509 cal wk~ 1 , female pupae 454 cal wk~1 , male adults 625 cal wk-l1 and female adults 735 cal wk-1 . The prepupa and pupa shed exuviae of 144 cal and 120 cal respectively. The average female produced 667 cal of eggs and 185 cal of egg-case material, which totaled 54% of adult female A. The annual energetics of the cohort of larvae was: C = 39,150, A = 32,642, F = 6876, Pg = 13,052, Pev = 3608, Pr= 359-409 and R = 15,982 cal m- 2