Hemolymph coagulation is a first response to injury, impeding infection, and ending bleeding. Little is known about its molecular basis in insects, but clotting factors have been identified in the fruit fly Drosophila melanogaster. Here, we have begun to study coagulation in the aquatic larvae of the malaria vector mosquito Anopheles gambiae using methods developed for Drosophila. A delicate clot was seen by light microscopy, and pullout and proteomic analysis identified phenoloxidase and apolipophorin-I as major candidate clotting factors. Electron microscopic analysis confirmed clot formation and revealed it contains fine molecular sheets, most likely a result of lipophorin assembly. Phenoloxidase appears to be more critical in clot formation in Anopheles than in Drosophila. The Anopheles larval clot thus differs in formation, structure, and composition from the clot in Drosophila, confirming the need to study coagulation in different insect species to learn more about its evolution and adaptation to different lifestyles.