Paddle crabs Ovalipes catharus (White, 1843) adopt five distinct opening techniques when feeding on the blue mussel Mytilus edulis aoteanus Powell in the laboratory. The particular opening technique used is influenced by bivalve size. Small mussels, <1.0 cm length are quickly crushed by the chelae and/or mandibles, while mussels between 1.0 and 3.0 cm are crushed across the umbone area or over the adductor muscle. Larger or more robust prey are opened slowly by wedging into, or chipping the shell until the minor chela gains access and is able to cut the adductor muscle. Handling times increased exponentially with mussel size, and resulted in a regular decrease in profitability (yield of flesh per unit handling time). Prey selection experiments, using equal ratios of mussels within the size range 0.5–3.0 cm length, showed that large and small crabs preferred a medium size prey. The preferred prey length increased with predator size, 1.0–1.5 cm for small crabs and 1.5–2.0 cm length for large crabs. Paired ratio experiments suggested the smallest mussels (0.5–1.0 cm) suffered reduced predation as they were often misidentified or obscured among the larger prey. Declining predation pressure on large mussels (2.5–3.0 cm) is the result of high rejection rates. Analyses of rejection times showed that 81% of larger prey were not rejected immediately, but handled further for periods up to 7 min. As encounter rates with small and large prey increased, handling times declined. The improvement of handling times suggests that Ovalipes catharus is able to learn or gain information by experience about the prey. This is the basis of a flexible search image, evidence of this foraging behaviour is discussed.