The dataset contains raw data of cell size, cell number, wing size and survival time of Drosophila melanogaster used for the analyses and to generate figures of the Insect Science paper (https://doi.org/10.1111/1744-7917.12742) by Verspagen, Leiva, Janssen and Verberk. The article investigated how different larval densities and rearing temperatures affected cell size and heat tolerance in the fruit fly Drosophila melanogaster. A detailed description of the experiments is given in the Materials and Methods of the paper. Data are organized in two Excel files. The first one contains cell size, cell number and wing size for each of the treatments used and the second one contain survival time data for four stressful temperatures. A description of each of the column is also given.