Butterflies mainly feed on nectar. Certain species may occasionally suck fluids from rotting fruits, mud, dung and carcasses.
The nectar is a thin sugary fluid secreted by flowers. The nectar chamber or the nectary is found surrounding the base of the ovary. Underneath the necatary, are specialized cells that secrete a sweet liquid. The nectar contains several substances other than sugars that impart a particular taste and odor.
The composition of nectar has been studied extensively. It has been found that the nectar varies from one plant species to another plant species. It is a balanced food containing carbohydrates, proteins, lipids (fats), minerals, vitamins and water. The carbohydrates are the major content of nectar. They occur as simple sugars such as, sucrose, glucose, lactose, maltose, fructose, besides arabinose, galactose, mannose, raffinose etc.
There are three types of nectar depending upon the composition of three important sugars, namely, sucrose, glucose, and fructose. Accordingly, there are nectars that contain mainly sucrose, nectars that contain mainly glucose and fructose and nectars that mainly contain all the three sugars, sucrose, glucose and fructose.
The proteins in nectar are identified as Nectarins. In addition, there are aminoacids such as alanine, arginine, serine, proline, glycine, isoleucine, threonine and valine.
The fats are in the form of oils. Other substances in the nectar include terpenes, alkaloids, flavonoids, glycosides, phenols, in small quantities.
The minerals are sodium, calcium, magnesium, aluminium, iron, and manganese.
There are vitamins and antioxidants also.
The nectar is watery and is secreted throughout the life span of flowers. There is a correlation between flower length, nectary size and total volume of nectar secreted by the flower. The volume of nectar is measured in micro liters (ul). The flower of Ipomoea alba is supposed to secrete the maximum quantity of nectar measuring 50 ul.