Mud puddling

Mud-puddling is the phenomenon mostly seen in butterflies and involves their aggregation on substrates like wet soil, dung and carrion to obtain nutrients such as salts and amino acids.
This behavior is restricted to males in many species. In tropical India this phenomenon is mostly seen in the post-monsoon season. The groups can include several species often including members of the Papilionidae and Pieridae. Following pictures were captured from the banks of Bhavani river in South India of Common Lime Butterfly(Papilio demoleus). 

Common Lime Butterfly(Papilio demoleus)

Males seem to benefit from the sodium uptake through mud-puddling behaviour with an increase in reproductive success. The collected sodium and amino acids are often transferred to the female with the spermatophore during mating as a nuptial gift. This nutrition also enhances the survival rate of the eggs.

Common Lime Butterfly(Papilio demoleus)

 Papilio demoleus is an aggressive and very common butterfly. It is perhaps the most widely distributed swallowtail in the world. The widespread range of Papilio demoleus indicates the butterfly's tolerance and adaptation to diverse habitats. It is to be found in savannahs, fallow lands, gardens, evergreen and semi-evergreen forests and shows a preference for stream and riverbeds.

Frost

Frost on the grass

If a solid surface is chilled below the dew point of the surrounding air and the surface itself is colder than freezing, frost will form on the surface.

In general, for frost to form the deposition surface must be colder than the surrounding air.Many plants can be damaged or killed by freezing temperatures or frost. This varies with the type of plant and tissue exposed to low temperatures.

Tender plants like the grass in the picture, die when they are exposed to frost. Cold-hardy plants, such as the plants in the higher elevations can tolerate extended periods of freezing. Eg- Rhododendron nilgiricum

Rhododendron nilgiricum in the higher elevation.

What causes such wide variations in the sensitivity of plants to cold?
As a consequence of natural selection, plants native to a particular hardiness zone are adapted to the temperature extremes that occur in their environment.
In fact, the most widely held explanation of frost damage in plants is that death is caused directly by the advanced state of cellular dehydration that results when ice forms in tissues.
According to this explanation when the concentation of water in cells falls below a critical "threshold" value, protein
molecules in the cells’ protoplasm begin to cross-link with each other, forming a stable but nonfunctional matrix. In this permanently altered state of protoplasm, metabohsm slows to a standstill and, since the cells die, the entire plant dies.
Apparently, species of plants that survive temperatures lethal to other species do so by preventing the dehydration caused by ice formation.

Finally, certain plants are cold tolerant simply because they can recover from even the extreme dehydration
that accompanies ice formation. Examples of such species is Rhododendron nilgiricum.


http://arnoldia.arboretum.harvard.edu/pdf/articles/1198.pdf