Female dance flies of the species Rhamphomyia longicauda suck in air and inflate their bodies to attract males. According to a new study by Rosalind Murray at the University of Toronto Mississauga and her colleagues, male dance flies are more attracted to larger females with hair-like scales on their legs.

The name dance fly comes from the aerial dance moves performed in mating swarms. Before going to the dance, each participating male captures an insect or weak male fly of the same species and wraps it in silk. The insect is a gift for the lucky female to feed on while mating.

The male dance flies, carrying their gifts, enter a swarm comprising of many suitors and dance in mid-air. There are over 3,000 species of dance flies around the world. Some, known as dagger flies, has a pointed mouth. Numerous studies of dance flies are on record, and many of them start from the dancing part.

The study mentioned above shows that female dance flies go to great length to attract suitors. They keep their hair-like pinnate scaled legs close to their bodies and fill the inflatable sacs along their abdomen with air to look bigger and hence more attractive.

The researchers theorize that male dance flies may interpret bigger and hairy to mean ‘full of eggs and ready to mate,’ which is why they prefer larger females over smaller ones.  The female flies above male swarms to demonstrate their beauty and allow males to make their pick and after pairing off, they fall from the sky ready to mate.

Researchers noted that females that are big and hairy are three times more attractive than smaller ones with less hairy. However, being scaled is more critical for dance flies with smaller air sacs.

Another factor influencing the suitor choice is the positioning of the female. Those dancing in the middle of the swarm are more attractive than the ones at the periphery, probably because predators such as spiders lurk at the edge of the crowd.

The study shows that not only males work to attract females in nature, the reverse is also true.