Apparently this is what a butterfly does when it "pees":

"Mudpuddling and Mineral Intake

Butterflies engage in a behavior called mudpuddling, where they gather on wet soil, animal waste, or even human sweat and urine to obtain salts and minerals essential for their metabolism During this process, they may release abdominal fluids as they balance their intake of liquids and nutrients. The expelled fluid can vary in color, consistency, and droplet size, depending on what the butterfly has consumed and its digestive processes. While butterflies do not pee in the traditional sense, they excrete excess fluids through their abdomen to maintain hydration and nutrient balance. This unique method of fluid release, combined with behaviors like mudpuddling, allows butterflies to thrive on a liquid diet without the need for kidneys or conventional urine production."