Sexual dimorphism is a common phenomenon in nature and can be seen across various fauna such as birds, insects and mammals. Basically, this means males and females exhibit different physical characteristics and this can be in the form of size, colour, structure and patterns.

In butterflies, these differences can be very subtle, where differences between the two sexes are minimal, or exaggerated, where differences are so prevalent that they may be assumed to be of different species. 

Colours or Camouflage?

In certain butterfly species, the male exhibits brighter colours and more decorated wing patterns compared to the female. One explanation for this occurrence is that since the male is responsible for courtship and searching for a mate, it needs to display traits that are attractive to a female while standing out among other male competitors. 

On the other hand, the female has the role of laying eggs and this may take several days to complete. Thus, it is crucial for the female butterfly to remain inconspicuous and reduce the likelihood of predation. Having duller, drabber wings will be more advantageous for the female for it to camouflage better with its surroundings. 

There are several butterfly species in Singapore that display sexual dimorphism. Here are three more commonly seen examples:

1. Horsfield’s Baron 

Photo credit: Khew Sin Khoon and Zhou Boyi 

In the Horsfield’s Baron (Tanaecia iapis), the male (above left) exhibits a velvety black upper side and a broad bright blue band along the margin of its hindwings. The female (above right) instead is a pale greyish ochreous brown and may appear similar to the Malay Viscount (Tanaecia pelea) and the Malay Baron (Euthalia monina).

2. Archduke

Photo credit: Jessica Teo

The Archduke (Lexias pardalis) is known to display one of the most exaggerated cases of sexual dimorphism in butterflies. The male and female look completely different from each other. The male is black with a wide blue marginal hindwing band while the female is larger in size, with bluish spots on its wings. It greatly resembles the less commonly seen female Yellow Archduke (Lexias canescens) although the latter is smaller in size and has yellowish underside hindwing scaling instead.

3. Leopard Lacewing 

Photo credit: Gary Chua

The sex of the Leopard Lacewing (Cethosia cyane) can be easily recognised by the colour of the upperside of the wings. The male butterfly’s wing is orange, almost resembling the Malay Lacewing (Cethosia hypsea) while the female is a pale creamy yellow. 

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