Small Mytilus edulis forced open by foot of N. lapillus. See image 39b 39b Nucella lapillus. Feeding on Mytilus edulis. North Cornwall, England. April 2008. Leg. & copyright N. Ward. for detail. Only small shells of M. edulis can be forced apart; larger specimens have to be bored for radula access, and those over 40mm long are rarely attacked in either way (Crothers, 1985).
Mytilus edulis is often most frequent prey of N. lapillus in extreme S.W. England, where the usually favoured prey, Semibalanus balanoides (barnacle), is rare or absent (settlement and survival vary greatly with weather from year to year, Lewis, 1964, pp.250-251). M. edulis may also be utilized in other areas on very sheltered shores where the sweep of fucoids restricts barnacle settlement.

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