Body size is one of the most important aspects of an organism’s biology and determines metabolism, a vital life function. Analyzing organism mass with respect to abundance is known as a size spectra analysis. Steeper size spectra slopes indicate less efficient energy transfer between trophic levels. Biological processes, such as growth and reproduction cycles, occur differently in temperate climates than tropical ones due to changes in influence of temperature and flow between these systems. However, temporal and latitudinal trends of community size spectra in lotic systems are less understood. To investigate how size spectra compare between tropical and temperate streams, we sampled macroinvertebrates in two river networks: one in Virginia, USA and one in Sao Paulo, Brazil. Using data from four evenly spaced sampling events throughout the calendar year, we produced community size spectra slopes to illustrate temporal patterns between the two river networks. Temperate sites had more variability over time and steeper slopes, whereas tropical sites had less biomass and consistent slopes between sites and time periods. Climate change is predicted to affect temperature and precipitation patterns, thus temporal studies such as this one are necessary to understand these trends.