Why do male butterflies visit mud puddles?

This study is the first to demonstrate that Na budgets of male and female Lepidoptera differ. At the time of emergence, male imported cabbage butterflies, Pieris rapae L., have significantly more total body Na than females. Older males collected from the field show a significantly lower level of body Na than freshly emerged males, whereas freshly emerged females and older, field-collected females show no difference. It is suggested that feeding from soil may help restore losses of Na in males. A single female, through oviposition, may lose nearly 75% of the total body Na with which it emerged. The lepidopteran mating system involving transfer of spermatophores is postulated as one causative factor for sexual differences in body Na levels.