The influence of 4 different factors on spatial distribution was tested experimentally: developmental stage, predator density, duration of site occupation and presence or absence of larvae of different developmental stages. Six parameters were used to characterize spatial distribution. — Three of the factors tested influenced spatial occupation in A. imperator: the size of home ranges increased with larval development, the coexistence of larvae of two different larval instars induced an increase of the volume occupied by medium-sized larvae and an instability of the home ranges of final-instar larvae, and the frequency of agonistic interactions increased with larval density. Analysis of the spatial distribution of aquatic insects is required to understand the dynamics of insects in aquatic environments (HILDREW et al., 1980; JOHNSON & CROWLEY, 1980; SPENCE & SCUDDER, 1980; ALLAN, 1982; HUGGINS & DUBOIS, 1982; MARTIN, 1985). Recent reports have stressed the value of an ethological approach towards interactions (between insects) for understanding modalities of spatial occupation (SIH, 1982; PECKARSKY & PENTON, 1985; SJOSTROM, 1985).