HAYASHI, Fumio (Dept. Biol., Fac. Sci., Tokyo Metropolitan Univ., Tokyo). 1985. Factors affecting the handling time of the dobsonfly larva, Protohermes grandis (Megaloptera, Corydalidae). Jap. J. Ecol., 35 : 1-11. Handling time, that is the time from biting a prey item with mandibles until completely swallowing it, of the dobsonfly larva Protohermes grandis, a predatory aquatic insect dwelling in the mountain stream, was measured under the laboratory conditions. It increased exponentially with the prey size. Size relation between the labium width of the dobsonfly larva and the body width of prey was important to determine the handling time. Water temperature affected the handling time (Q_<10>=3.8), but the degree of hunger did not affect it. The kind of prey was another important factor affecting the handling time which was changed by the difference in shape and hardness of prey. In addition, prey profitability was estimated based on the handling time/dry matter gain. There was the most profitable prey size for the dobsonfly larva, at which the time required to eat 1 mg dry weight of prey was minimized. This most profitable prey size was independent of water temperature, but changed by the difference of prey kinds.