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Today is all a buzz with romance. It’s not just humans that perform grand gestures and surprise partners with gifts, for many other animals adopt elaborate courting rituals to woo a mate. There are balletic butterfly displays, pebble gifts from penguin companions, decorated bird nests and even serenading flies!

This Valentine’s Day, we reveal flies supposed charming side as we focus on their mating behaviour. Probably more typically thought of as an irritating pest and one responsible for the spread of diseases, but when it comes to wooing, it turns out that flies have some remarkable qualities.

Fly on the wings of love

Flies are ‘flirting on the fly’ according to research published in BMC Biology by Courtney Eichorn and colleagues from Simon Fraser University.  They found that female green bottle flies attract potential mates by flashing sunlight at particular frequencies from their wings.

Sunlight reflects off flies’ wings as they fly with one reflected light flash per wing beat. This creates flashing signals, and flies can evaluate the frequency of the wing beats to gain information about the sex, age and even mating status of another fly. Males use this to find a mate, as the frequencies of wing flapping differ between desirable young females (178Hz), and the less desirable old females (253Hz), young males (212Hz) or old males (266Hz).

The team discovered this behaviour by filming young and old male and female flies in free flight to capture and measure wing flash frequency, and suggest that males favour light flash frequency to morphological characteristics of the females.

Given an exceptional rating by Faculty Member, Etienne Joly, in his recommendation: “Eichorn and colleagues uncover a new type of sexual recognition signal in flies, which provides a cool explanation for this, relying on the beat of wing flapping by female flies.”

“Did you know that male green bottle flies are not easily turned on on cloudy days?” asks Joly, referring to the finding that male green bottle flies only pursue females on sunny days, as light flashes can’t be seen on cloudy days. This indicates that flies synchronize their sexual communication based on environmental cues.

The song of the fruit fly

An unlikely singer, but even male fruit flies serenade females to impress them, were the findings of Philip Coen and colleagues from Princeton University in Nature. Male fruit flies pursue females while in flight. The males produce a song by vibrating their wings to attract females’ attention and females react to song features.

Lars Chittka and Sylvain Alem, Faculty Members from Queen Mary University London, UK, explained in their recommendation: “The use of structured and patterned courtship song to attract potential mates is widespread in the animal kingdom. In some species, however, song structure can vary considerably, giving rise to a seemingly improvised, random courtship song. Neural noise has been supposed to generate this randomness in signal production.”

The males’ song was thought of as a fixed action sequence with the females simply acting as a stimulus, but this research found that there is variability in the renditions. The males use visual cues to shape their song pattern, based on the distance between the male and female fruit fly, and lateral speed of the female. For example, the male might choose a louder song when the female is far away to increase the chance of gaining her attention.

The fact that males can improvise the courtship song indicates that they are capable of rapid-decision making based on environmental sensory cues, showing that the mating behaviour is neurally controlled.

A matter of life and sex

Evolutionary biologists have known that aspects of reproductive processes can affect ageing and physiology. Research published in Science by Christi M. Gendron and colleagues from University of Michigan, Ann Arbor, revealed that even just the detection of sexual pheromones from a female fruit fly can trigger changes in the metabolism of the male fruit flies. The males detect this though a sensory receptor in their foreleg neurons and it causes their fat stores to decrease rapidly, reduces their resistance to starvation, and it shortens their life span.

“A remarkable and innovative study” according to Faculty Member, Thomas Flatt, University of Fribourg, Switzerland. Flatt recommended the article because it is “compelling evidence that simply the perception of sexual pheromones of the opposite sex alone can be sufficient to induce such survival costs of reproduction.”