1. Temporal summation was measured in green-sensitive photoreceptors of seven hymenopteran species with various life styles: three bees, Melipona quadrifasciata quadrifasciata, Trigona spinnipes and Bombus morio; one wasp, Polistes canadensis; and three ants, Pseudomyrmex phyllophilus, Camponotus rufipes, and Atta sexdens rubropilosa. In all species approximate agreement with Bloch's law was confirmed. 2. Critical durations (tc), which varied from 10 ms (Pseudomyrmex) to 46 ms (Atta), are discussed in relation to the life styles of the species and to the mechanisms causing the differences. 3. The direct measures of critical duration obtained are compared to estimates made by convolution or integration of impulse responses measured here in one species and from published data. Linear convolution of typical impulse responses is shown to result in significant departures from Bloch's law, a fact that seems to have been overlooked in the literature. 4. The method used to measure temporal summation involved recording responses to 300-ms stimuli at various intensities; the form of these responses varied greatly from species to species. Possible causes of these variations are discussed.