Despite the large amount of information available on host plant preferences by butterfly larvae, we still know quite little about what determines the number of plant species they visit as adults when searching for nectar in flowers. Here we examine the patterns of nectarivory by butterflies at five Spanish sites, encompassing a wide range of biotopes.  A large data set of flower visitation has been gathered throughout a period of 11 years of monitoring butterflies. Specifically, our main aims are: (1) to evaluate their degree of generalism, and (2) to determine the influence of different butterfly life history traits (index of abundance, phenology, larval polyphagy, voltinism, habitat specialization, wing length, mobility) in such generalism. We compare different habitats (forest vs open biotopes) in order to (3) assess whether generalism levels and their influencing factors vary among them, and (4) to know how consistent is the degree of generalism for species living in several habitats. Finally, we test whether the most specialist butterflies are those most likely to be of conservation concern (as found in a previous study in the UK, Tudor et al. 2004).

Results/Conclusions

Of the 104 species monitored in total in the five localities, we could classify 43 (41.35%) as generalists and 61 as specialists (58.65%). Despite the higher diversity of butterfly species in forested areas, a similar proportion of specialists and generalists were found in them. By contrast, we found a higher proportion of specialists in open areas than expected. Interestingly, a number of species act as generalists or specialists depending upon the habitat in which they are found. For most sites, phenology as well as index of species abundance (estimated independently) showed to be the main factors determining the number of plants butterfly interact with when nectaring, although species habitat specialization also was relevant in some cases. The number of host plants on which butterfly larvae feed was consistently irrelevant in all models. As expected, significant differences existed among butterfly families in their degree of generalism. We did not find that the most specialist flowers users are butterflies listed in the Red Book of European Butteflies.