Common Mormon (female form)

Normally a jet black butterfly with row of white spots along the middle part of hindwing. 90–100 mm. This one was more of a dark brown.

In India, this butterfly is considered as the classic example of Batesian Mimicry in which edible species resemble unpalatable butterflies in order to escape being eaten by predators.
The populations of the mimicking morphs of the Common Mormon are much smaller than that of their models - the Common or Crimson Rose. This is in order to allow first time predators a much greater chance of preying upon the unpalatable model in the first instance and thus learning of their inedibility.
Larger populations of mimics could result in the edible Common Mormon mimics being sampled the first time by predators. If this should happen, the predator may not realise that butterflies of that colour and pattern are protected by the poisons they ingest; thus dramatically reducing the effectiveness of this scheme of protection.

Female:
The female of the Common Mormon is polymorphic. In South Asia, it has three forms or morphs.

This one is the Form romulus.
This female form mimics the Crimson Rose and is common over its range. The romulus form is duller than its model, the Crimson Rose. It is easy to differentiate the mimics from models by the colour of their body—the models are red-bodied and the mimics are black-bodied.

Male:
The male has one morph only. It is a dark-coloured swallow-tailed butterfly. The upper forewing has a series of white spots decreasing in size towards the apex. The upper hindwing has a complete discal band of elongated white spots. It may or may not have marginal red crescents. The males are generally smaller in size than the females but not always. Both male and all forms of the female of P.polytes can vary considerably in size depending on climatic region.
Source: Wikipedia