Ventilation of Tracheal System – Passive Suction Ventilation
Many active insects and insects that live in environments where water is scarce cannot depend on diffusion alone to obtain their oxygen. Flying insects need a steady supply of oxygen; therefore, their flight muscles are richly supplied with tracheoles. If the spiracles of such insects were to be kept open they would lose all their body water.
To solve this problem there is control of volume of air and the direction of flow through the system. For example locusts maintain a flow of air through the spiracles by muscular contraction and accurately timed opening and closing of various spiracles. The air enters through the anterior spiracles and leaves by the posterior spiracles establishing a uni direction flow of air. However, gas exchange in the tracheoles is through diffusion only even in-the largest and most active insects.