Local enhancement in mud-puddling swallowtail butterflies (Battus philenor and Papilio glaucus)

Male butterflies aggregate at moist soil to acquire nutrients, a phenomenon termed "mud-puddling." We studied the attraction of free-flying Papilio glaucus and Battus philenor swallowtails to dead decoys of those two species at artificial puddles moistened with NaCl solution. Both species landed preferentially at puddles with a decoy present rather than at unbaited puddles, demonstrating very strong local enhancement, a form of social facilitation. Papilio glaucus were attracted only to intraspecific decoys, whereas Battus philenor exhibited both intraspecific and interspecific attraction. Circular discs cut from the hindwings of male Battus were highly attractive to male Battus but completely unattractive to Papilio glaucus. The visual cues attractive to males in their search for salts differ between these two swallowtail species for unexplained reasons.