Significance Mosquito blood cells are central players of immunity against the vector-borne pathogens that devastate the lives of millions of people worldwide. However, their molecular identity and classification remain controversial. By applying single-cell RNA sequencing and high-content imaging flow cytometry, we defined the molecular fingerprint of a subset of mosquito blood cells and characterized two transcriptionally distinct blood cell populations that resemble previously described cell types. Surprisingly, cell population analyses at a single-cell level uncovered an active molecular transfer between the two cell types that may contribute to cellular diversity and plasticity seen across biological systems.