Many times we see butterfly sitting on the ground or some rotten waste but mostly on the soil . So why does this happen.
Apart from nectar, butterflies also need salts like sodium and some essential amino acids for their growth, mating and other physiological demands. To meet this demand butterflies take up this nutrient from wet soils, carrion(rotting meat) . In some cases they are also attracted to the sweat from the human body.
This activity is generally termed as mud-puddling. It gets to be sighted more often in post-monsoon season when the soil is wet all around. Males benefit from the sodium uptake through mud-puddling as it helps increase in reproductive success. During mating the collected sodium and amino acids are often transferred to the female with the spermatophore, which helps in survival of the eggs. Recent studies reveal that those minerals also responsible in the neuromuscular activity, therefore it is important for their flight movement as well. Butterflies also take up this kind of minerals,salts from rotten meat and animal wastes . Sometimes in humid weather condition when its quite sweaty the butterflies get attracted to the humans as they take up nutrients from the sweat.
So commoners might find it quite unusual but its a part of their physiological system.
In this image a butterfly named , Angled Pierrot is trying to take up nutrients from the bird poop in the middle of a wet tar road.