In order to acquire a mate, male butterflies have to make sure they are attractive enough. For this purpose, they have to gather certain resources. The resources include minerals from soil - salts mainly. Many a times we see male butterflies in large numbers on a patch of soil, animal dung or on such other surfaces. This is called 'mudpuddling'. The groups of mudpuddling butterflies mainly consist of males in search of their "resources". The salts they suck up are an essential requirement in the production of healthy eggs. These salts get concentrated as nutrients in compact capsules of 'spermatophores' which are passed on to the female while mating.
Here are some mudpuddling male Blue bottles with a Red helen as well :)
Sometimes, milkweed butterflies(like Plain tiger, Blue tiger, Common crow) are seen sucking from damaged parts of plants like Crotolaria or Heliotropium. The sap of these plants contain alkaloids that are essential for the production of mate-atttracting chemicals called 'pheromones'.
While searching for a mate, male butterflies strategically plan their outings, and often search around food plants to find newly emerged females. When a male finds his female, he tries to impress her with a series of wing displays and dispersal of pheromones. Then the male might touch the female and promt her to mate. At this point, the female might mate with the male, or might reject him by lifting her abdomen.
When I had been to Mekedaatu (approx 90km from Bangalore) I photographed this pair of crimson tips. They flew around for some time, and they were flying in circles. So I thought they were going to mate very soon. I got ready with the camera as they settled down. And right then, the female rejected him by lifting up her abdomen. This is the picture I could manage: