Mud-puddling behavior in tropical butterflies: in search of proteins or minerals?

We experimentally investigated the attraction of adult butterflies to moist soil and dirt places (a behavior termed 'mud-puddling') in two species-ric h tropical communities on the island of Borneo. At a rain forest site, 227 individuals (46 species) were attracted to the baits, compared to 534 indiv iduals (54 species) at a farmland site. With one single exception, all attr acted butterflies were males. Of various salt and amino acid solutions, onl y sodium was accepted, but overall, albumin solutions turned out to be the most attractive puddling resource. Butterfly families differed consistently in their resource preferences. Representatives of the families Papilionida e and Pieridae more often visited NaCl solutions, but still accepted albumi n, whereas representatives of the Nymphalidae, Hesperiidae and, in particul ar, Lycaenidae preferred the protein resource. In experiments using decoys prepared from pinned butterfly specimens, representatives of the Papilionid ae and Pieridae were more strongly attracted to baits provided with decoys made from conspicuous, medium-sized yellow Eurema species (Pieridae), where as dummies made from small, cryptically colored lycaenids (Prosotas and Cal eta species) were ineffective. Decoys did not influence the attraction of l ycaenid butterflies towards baits. Hence, visual cues pla) an important rol e in locating puddling resources for papilionids and pierids, while for lyc aenid butterflies searching for nitrogen sources, olfactory cues emitted by decaying organic matter are more likely to be important. The strong attrac tion of male butterflies to nitrogen-rich resources suggests that, as in th e case of sodium, these nutrients may increase reproductive success.