Flight requires a lot of energy, and butterflies get most of the calories they need from the sugars found in flower nectar. The best flowers produce nectar with 20-25% sugar content and store it in chambers that can be easily penetrated by the butterflies’ uncoiled proboscis, or sipping straw-like mouth part. Suitable blossoms also provide a good landing pad on which to feed. Among the favorites are asters, daisies, milkweeds, mustards, mints, peas, and vervains.
While nectar forms the bulk of a butterflies’ diet, they also need other food sources. Besides sugars, they need salts, nitrogen, amino acids, and certain chemicals used for making sex attractants. Butterflies are very opportunistic creatures, and so their grocery list includes tree sap, wet soil, flower pollen, rotting fruit and vegetables, carrion, mammal dung, urine, bird droppings, slug slime, tears, sweat, and other animal secretions. These items do not come to mind when we think of colorful, frolicking butterflies.
Butterflies have a mating process that involves providing a “nuptial gift”. During copulation, the male transfers a spermatophore, a capsule of nutrients, salts, and sperm, to the female. This is no small gift, as a spermatophore can weigh 10 to 50% of the male butterfly’s own weight. The female depends on it for the materials necessary to provision herself and her eggs, and allows her to devote more time to locating host plants on which to lay them.
To find the chemical compounds essential to the nuptial gift, male butterflies are the ones most often found clustered around urine soaked ground or cow piles, forming what has been named “puddle clubs”. These waste products are a cornucopia of nitrogen, amino acids, salts, and sugars. To an unmated male butterfly, such food sources are equivalent to very fine dining. Decaying carcasses are even better.
Information for this article was acquired from “Butterfly Buffet”, Natural History Magazine, July 2001 issue, page 46. This is a good magazine for nature lovers.