Butterflies have an odd quirk in their mating practices: during warm months, the males pursue the females, but when it's cold, the females go after the males. This unusual reversal is a matter of life and death for the females.


Yale researchers were curious to figure out why female squinting bush brown butterflies had beautiful ornamental patterns on their wings, just like their male counterparts. In most species, males have the eye-catching plumage or patterns, which they use to attract the interest of females during mating season. In most species, females are the passive party in mating rituals, so they don't need their own beautiful plumage.

The researchers hypothesized that there were certain situations where female butterflies did take an active role in mating, and they further guessed that there might be environmental reasons for the change. They gathered up some butterfly larva and placed them in two artificial environments, with one area set for 27 degrees Celsius and the other at 17 degrees.


The first set of conditions, which is very similar to the warm, wet season of the butterflies' native African habitat, produced the expected response, as males used their ornamental wings to attract the attention of females. But the situation was reversed in the cooler conditions, as the females now had to use their patterned wings to entice males to mate with them.

So why this unusual role reversal? Researcher Kathleen Prudic says that male butterflies provide not just sperm but also nutrients to the females during mating, and these nutrients are crucial to the survival of the females during times that aren't great for reproduction, such as the cool, dry season.

This means that it's a matter of survival for females to attract a mate during this time of year, and they can no longer afford to be picky about their mates like they can when it's warm and wet. Males, on the other hand, have to be careful with their nutrients, as the more they give away to mates the shorter their own lifespan becomes.