Hemocytes are an essential component of the invertebrate innate immune system (Strand 2008). Their close similarities to vertebrate white blood cells enable their use as a tractable model for immunological research. The quantification of hemocytes in the hemolymph (invertebrate blood) is one way of assessing the efficacy of the immune response, as the absolute number of hemocytes changes during the course of an infection (Bergin et al. 2003, Brayner et al. 2007), and the density of hemocytes in the hemolymph is strongly correlated with the capacity to encapsulate or phagocytose parasites (Eslin and Prevost 1998, Kraaijeveld et al. 2001, Wilson et al. 2003; Costa et al. 2005). Most researchers continue to use cell staining and manual microscopy techniques to enumerate the hemocytes in a given sample. However, given the laborious nature of this method (with a throughput often as low as 6–8 samples per hour), more rapid techniques are required to increase our understanding of the role of hemocytes in invertebrate immunology. Here, we tested the suitability of the Bio-Rad TC10 automated cell counter, a tool originally developed for assessing mammalian cell counts, for counting insect hemocytes. Hemocyte counts from the model insect species Spodoptera littoralis (Lepidoptera: Noctuidae) were compared with those obtained using a traditional tool for counting insect hemocytes: a hemocytometer with improved Neubauer ruling under light microscopy. We then tested the capacity of the Bio-Rad TC10 cell counter to distinguish among cell counts in insects fed on artificial diets varying in their protein and carbohydrate contents, which has previously been shown to influence hemocyte counts in this species (Ponton et al. 2011).