By Ella Davies
Earth News reporter
Older female butterflies spend up to 55% of their day flying in order to catch the attention of a mate, scientists have found.
Researchers studying speckled wood butterflies observed virgin females acting more conspicuously as they aged.
While they still had enough lifespan left to lay and feed their eggs, females increased their activity - apparently in order to attract a mate.
Males used "sunspots" as vantage points from which to observe female flights.
The study, published in the journal Animal Behaviour, sheds new light on the mating behaviour of this common European species.
In the past, researchers have identified two types of mating behaviour in male butterflies: patrolling and perching.
Patrolling males seek out females for mating "on the wing", whereas perching males are known to remain in one place.
Male speckled wood butterflies have been identified as "perchers" but less is known about the role females play.
"The mating system of a species is very much the interaction of male and female behaviour," says graduate student Martin Bergman.
By observing their behaviour over two months, Mr Bergman and his colleagues found that older unmated females spent 35% more of their time flying than mated and younger virgin females.
Mr Bergman explains that his results compliment existing theories surrounding the "evolutionary cost" of females remaining unmated.
"The theory of sexual selection suggests that for a butterfly female, there is a cost of being unmated for a long time, since the time left for egg laying and feeding decreases," he says.
"Our study is, to my knowledge, one of the first to empirically show how [butterfly] females change their behaviour according to age."
Male speckled wood butterflies defend their sunspots fiercely. They use them as vantage points to watch for females.
The butterflies engage in spiralling flight contests to determine territories.
Previous studies indicate that male speckled wood butterflies compete for "sunspots" on the forest floor where light breaks through the canopy.
Researchers theorised that unmated female butterflies would travel to these territories in order to find a mate.
However, this new evidence suggests that the highly prized sunspots do not attract females as first thought.
Instead, the sunspots are thought to provide vantage points where male butterflies have the best chance of seeing unmated females in flight.
With this increased visual detection, males are then able to pursue females with minimal effort and a high chance of mating success.