Sinking speeds of falling and flying Aphis fabae Scopoli

Abstract. 1. The terminal velocities of freshly anaesthetized and weighed, virginoparous alatae were measured by dropping them into updrafts of known speed. For an average specimen weighing about 0.49 mg the terminal velocity was 1.78 ms ‐1 with wings closed and 0.82 ms ‐1 with wings fully extended horizontally. 2. Extrapolating from the known terminal velocities of falling spheres of appropriate density, it is concluded that for inertly falling insects of constant shape the terminal velocity will be substantially lower with the wings extended than with them closed for all sizes of insect and that the horizontal distance travelled during a fall will be correspondingly greater. 3. Sudden reflex immobilization and falling was sometimes observed in aphids flying in a laboratory flight chamber, and very occasionally this immobilized state was maintained for many seconds (even during handling) before recovery and renewed flight. There was no evidence of a special falling attitude (‘Fall‐reflexhaltung’) other than a simple ‘frozen flight’ attitude with wings extended horizontally and legs extended fore and aft while the insect spiralled downwards, abdomen first. 4. The flying aphid's usual response to a coloured surface below it in the flight chamber was not to cease wing‐beating and fall but to fly downwards, abdomen first, at speeds up to more than 0.7 m s ‐1 .