The effects of omnivory on population ecology are rarely studied, although scavenging can be expected in species that are obligated herbivorous to supplement dietary needs for improving their fitness and/or performance. In one field and two laboratory experiments scavenging effects on growth and reproductive success (mating frequency, daily number of eggs per female, hatching rate) of and the attraction to carrion were investigated for the intertidal herbivorous periwinkle Littorina littorea. In the field, M. edulis with cut adductor muscles (= opened; representing carrion) were significantly more frequently contacted by L. littorea than either intact M. edulis or Ulva lactuca, with no significant differences in contact frequency between the latter two. In the laboratory, L. littorea that were exclusively offered opened M. edulis grew significantly less than conspecifics that were either offered U. lactuca alone or that were kept on a mixed diet (= opened mussel and U. lactuca). Regarding reproductive output, L. littorea produced fewer eggs when offered opened M. edulis than conspecifics that were either kept on a mixed diet or exclusively on an U. lactuca diet. Mating frequency and hatching success of eggs was not significantly different between L. littorea kept on the three diets. Our results confirm a NW Atlantic study showing that L. littorea was attracted to carrion. Yet, missing significant differences in growth and reproductive output of periwinkles that were or were not allowed to scavenge (= mixed diet vs. exclusively U. lactuca fed) suggests neutral scavenging effects on periwinkle fitness and performance. Perhaps, scavenging by periwinkles could be important at higher levels of ecological organization, due to an increase in the frequency of interspecific interactions and/or a facilitated flow of energy and matter, all of which should add on stabilizing food web structure.