A simple funnel trap which inverts on entry to and exit from the water, was evaluated with respect to sampling the aquatic fauna of wells in and around Fortaleza, Brazil. Mosquito larvae, copepods, ostracods, fish and tadpoles were collected. When known numbers of Culex quinquefasciatus larvae and Mesocyclops aspericornis copepods were introduced into negative wells, overnight sampling resulted in 50% positivity of traps when 10 larvae (1/1,000 cm2) and 25 copepods (1/176 liters) were introduced. All traps were positive when 100 and 400 larve and copepods, respectively, were present. Over a range of 10-2,000 and 25-800 released larvae and copepods, respectively, average recovery rates were 6.1 and 3.6%, but on the basis of one sample, the variability was such that a precise estimate of absolute abundance could not be made.