In the study the preference of two Littorina species, i.e. Littorina obtusata and Littorina fabalis was investigated experimentally and in the field on which of the two fucoid species, Fucus vesiculosus or Ascophyllum nodosum they preferred to place their egg aggregations. The hypothesis tested was that L. obtusata and L. fabalis both prefer F. vesiculosus as substrate for spawning over A. nodosum and that L. obtusata move from their main grazing habitat, i.e. A. nodosum to F. vesiculosus before laying their egg sacs. The experiment was supported by a field study where the numbers of the two Littorina species, both adults and juveniles, were counted on F. vesiculosus and A. nodosum thalli collected in the field.  The results showed that both L. obtusata and L. fabalis preferred F. vesiculosus over A. nodosum as substrate for placing their egg sacs and that juveniles transfer to their preferred food source after hatching. This is the first report on the ability of adult L. obtusata to actively select favorable substrate for juvenile snails, by avoiding placing their egg sacs on unfavorable surfaces as A. nodosum. Both L. fabalis and L. obtusata placed their egg sacs on older parts of the thalli, mostly below the vesicles. The number of eggs sac was higher for L. obtusata when both A. nodosum and F. vesiculosus where available, but higher for L. fabalis when there were only F. vesiculosus in the jar. This indicates that more of the preferred nutrition would provide for more eggs in each sac, since the adults have more energy to produce more eggs. The number of snails counted in the field shows the dynamics of population during the summer. There was an obvious shift with more juveniles of both Littorina species on F. vesiculosus in the beginning of July, changing to most of the juveniles occurring on A. nodosum at the end of the month.  The importance of conducting the study during the hatching season to monitor the movements of the snails between preferred habitat for adult grazing, spawning and juvenile feeding is evident.