Macrophages tightly control their phagocytic capacity, limiting intracellular overcrowding. However, the molecular details of this adaptive response remain undefined. Here, the authors combine live in vivo imaging with fly genetics and show that, in phagocytic Drosophila macrophages, mechanical and molecular adaptations of the nucleus to the indenting phagosomal cargoes are required to sustain macrophage phagocytosis in vivo.