Predation of manila clams (Ruditapes philippinarum) by swimming crabs (Portunus trituberculatus) and Japanese stone crabs (Charybdis japonica) was compared in the laboratory under different starvation regimes by a video recording analysis system, and the mechanism of foraging behavior differences between them combined with ethograms and morphology characteristics was discussed. The main results were as follows: (1) Starvation had a significant effect on P. trituberculatus and C. japonica predation rates. With the increase of the starvation regime, predation rate tended to increase at first and then decrease. Under starvation for 6 days, their predation rates were 4.5 clams day(-1) and 5.5 clams day(-1), respectively. (2) Their foraging time budgets were significantly affected by starvation. The handling time per clam of P. trituberculatus (10.9 ± 4.7 min) was higher than C. japonica (5.3 ± 3.0 min), but the difference was not significant. (3) Encounter rate and the probability of capture upon encounter between P. trituberculatus and clams were significantly affected by starvation. The probability of capture upon encounter of P. trituberculatus was approximately 10 times the probability of consumption upon capture. Encounter rate and the probability of consumption were important components in the swimming crab-clam system. The probability of consumption upon capture between C. japonica and clams was significantly affected by starvation. The probability of consumption upon capture was an important component in the Japanese stone crab-clam system. (4) Relative frequencies of transition from stationary to moving and from searching to handling of P. trituberculatus were significantly affected by starvation. As for C. japonica, the relative frequency of transition from searching to handling was significantly affected by starvation. It revealed that the component regulating predation rate variation under starvation between swimming crabs and Japanese stone crabs was different, which was caused by morphological segregation due to the long-term evolution in their habitats.