[Photo] Here a wet-season female butterfly (left) mates with a dry-season male. Credit: William Piel & Antonia Monteiro.


A chill may be just what butterfly lads need to bring the ladies fluttering to their knees.

New research finds that when exposed to cool, dry temperatures as caterpillars, female butterflies, which are used to being on the receiving end of the love chase, actively courted males when mating time rolled around.

On the other hand, if butterflies were raised in the moist and warmer season as larvae, males took up the traditional role of suitor, displaying their wing designs to females that do the choosing.

"Behavior in these butterflies is changed by the temperatures experienced during development," said study researcher Kathleen L. Prudic of Yale University.

The research began when scientists noticed that female squinting bush brown butterflies (Bicyclus anynana) had the same ornamental eye-shaped patterns on their wings just as males did. In most species, males end up with often elaborate and colorful ornamentation to attract mates, while the gals wear drab coats.

The researchers theorized that perhaps courtship behavior would change given different environmental conditions. They tested the behavior of butterflies raised in their larval stage (caterpillars) at 80.6 degrees Fahrenheit (27 degrees Celsius) and at 62.6 degrees F (17 degrees C).

When they observed the different populations, they noticed that, as expected, the female butterflies raised in warm temperatures were more likely to mate with males with ornamented wings. However, in cooler, dryer climates, the researchers saw that females played the role of suitors and flashed their eye spots to choosy males.

When scientists studied the wing spots, which reflect light in the ultraviolet range, they found the spots were brighter in the courting females than in pursued males from the cooler season, and compared with females that had been raised in the hotter season.

The researchers believe that this effect is a survival tool. In addition to delivering sperm during the mating process, male butterflies also deliver nutrients. In less than optimal times for reproduction (the dry, cool season), these male offerings appear to lead to increased female longevity.

Females want to survive through the dry season and so they furiously display to as many males as possible in order to obtain these resources. For male butterflies, the mating process and transfer of nutrients has the opposite effect. As a result, they become very careful about choosing their mates, getting busy with only the select few females with the brightest eyespots.