Why, even though they have an open circulatory system, can flying insects like flies beat their wings with great speed?
In insects the circulatory system is open but this system does not participate in the gas exchange process and in oxygen supply to the tissues. Gases go in and out by the independent tracheal system that permits direct contact of cells with the ambient air. Thus an insect can supply the great oxygen demand of its fast-beating wing muscles even having open circulatory system.