File:Catopsilia pomona (yellow) and Graphium doson (black and blue) butterflies mud-puddling - 20100616.jpg

English: The yellow butterflies are Common Emigrants, also known as Lemon Emigrants (Catopsilia pomona). This is a medium sized pierid butterfly found in Asia and parts of Australia. The species gets its name from its habit of migration. Some early authors considered them as two distinct species, Catopsilia crocale and Catopsilia pomona.

The black and blue butterfly is a Common Jay (Graphium doson). This is a black, tropical papilionid butterfly with pale blue semi-transparent central wing bands that are formed by large spots. There is a marginal series of smaller spots. The underside of wings is brown with markings similar to the upper side but whitish in color. The sexes look alike.

(Thanks to Vivek, Naveena and Bala Sir for confirmation of the identity of the butterflies.)

Mud-puddling is a phenomenon mostly seen in butterflies that involves their aggregation on substrates like wet soil, dung and carrion to obtain nutrients such as salts and amino acids. This behaviour has also been seen in some other insects, notably the leafhoppers.

Lepidoptera (butterflies and moths) are diverse in their strategies to gather liquid nutrients. Typically, mud-puddling behavior takes place on wet soil. But even sweat on human skin may be attractive to butterflies. The most unusual sources include blood and tears.

This behaviour is restricted to males in many species, and in some like Battus philenor the presence of an assembly of butterflies on the ground acts as a stimulus to join the presumptive mud-puddling flock.