Fruit fly sex: the hot and heavy details

The last time I did a piece on my fly sex research, I skirted around the question that you were all thinking; what does fruit fly sex look like?

Okay, here goes:

In most species, (and no, I’m not talking about the human species right now) it’s the females who choose which males they want to mate with. My fruit fly friends are no exception.

Why is this?

It all comes back to sperm and eggs. Think of the game of reproduction like a marketplace. The end goal of both sexes is to spread their genes, aka have babies.

Sperm are relatively ‘cheap’ to produce (sorry guys). They are small cells that don’t take much energy to make. And males make lots of them. All the time.

Eggs are huge, bulky cells full of nutrients. They are energy-intensive to make, and females don’t make very many of them. This makes eggs more ‘expensive’ than sperm.

In addition, some female animals carry their young inside their bodies, feeding them through their bloodstream. This takes lots of energy. So does caring for and feeding these babies once they come out into the real world.

In short, making babies is ‘expensive’ for females and ‘cheap’ for males.
Because females are so invested in reproduction, they are looking for males with the very best genes. These males will pass their terrific genes to the female’s offspring, increasing the chance that her babies will survive long enough to have babies of their own.

Reproducing before you die is basically the end goal in evolution. The natural ‘meaning of life’ if you will.

Did I lose anyone? Back to the fruit flies!

In fruit flies, it is up to the males to impress the females. How do they do it? Through dance.

I’m not kidding.

Watch this video by Dylan Clyne, and you’ll see what I mean. The fly with the black butt is the male.

First the male chases the female around trying to get her attention. Then he extends one wing and vibrates it. Apparently females are fond of this. Biologists call it ‘wing song’. Maybe it’s a romantic serenade or a pop ballad, you never know.

He also gets close and lets he rub her legs along his body. This isn’t a mere caress. She’s smelling him, and deciding if he’s up to par. The bodies of fruit flies are covered with waterproof waxes. These waxes also contain pheromones which the female experiences through touch. Every male has a different combination of pheromones, so each ‘smells’ slightly different to the female.

Finally, the male jumps onto the female’s back and attempts to mate with her. Sometimes this works, sometimes it doesn’t.

If you watched the video, you’ll have seen that the female is larger than the male. That’s pretty common in the insect world. Scientists don’t agree why this is. Evolutionary Ecologist Wolf Blanckenhorn proposes that while females bulk up so they can be better mothers, males focus on growing their reproductive organs, which are both complex and massive compared to the size of their body. Ain’t evolution grand?

Okay, the female fly is bigger than the male. This means that if a female has no intentions of mating with the male who has had the audacity to climb on her back, she can forcibly remove him.

She does this by shaking her body vigorously, sending him flying through the air.

Without a doubt, this is the most fun part of fly mating to watch.

The males always look so confused and flustered when they’re sailing through the air.

Often the male doesn’t quite get the message, and tries it again. After 2-3 attempts he gives up and searches for greener pastures.

There you have it, more details about fruit fly sex than you could possibly want! As well as some info on reproductive evolution that you probably didn’t want either, but have to admit is pretty cool.

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About Amelia

I am a recent biology graduate and current journalism student exploring career opportunities in science communications.

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