So I kept at it. Curious. In other days I might have skipped over the passing query and simply let it drop into that pile of things you wonder about but never quite check up on. But these strange coronavirus days, with so much time on our hands, I found myself unwilling to let the question of the sex lives of butterflies go just like that. Sadly the butterfly movie didn’t have the answers, though I did give it the full 45 minutes viewing time. After which, a bit more nosing around online revealed some astonishing finds!
New studies of the lowly cabbage white butterfly “have shown that the sex life of a seemingly unremarkable butterfly is utterly remarkable. It features sperm packages of ungodly size. It involves genitals that double as a souped-up stomach. There’s even an honest-to-goodness vagina dentata.” (Yong, 2017) Oh my!
spermatophores & copulatrixes
A cabbage white’s ejaculate is very different from a human’s. Rather than a blob of white gunk, it’s a complex solid package called a spermatophore, which consists of a hard outer shell, soft nutritious innards, and a ball of sperm at the base. The male deposits this into a pouch within the female reproductive tract called the bursa copulatrix. Once inside, the sperm swim off into a second pouch—the female will later use these to fertilize her eggs. Meanwhile, she starts to break down the outer shell of the spermatophore to absorb the nutrients within. So, the spermatophore acts as a nuptial gift—a way for the male to nourish the mother of his future offspring, long after he flies away.
As gifts go, the spermatophore is a substantial one. On average, each packet makes up an astonishing 13 percent of the male’s body weight. “Scientists who work on ejaculates will often show up to meetings with props,” says Morehouse. “I’ve never had it in me to bring a five-gallon bucket along. But that’s what we’re talking about [if you scale it up to human size]. It’s a water-cooler-sized ejaculate.” (Yong, 2017)
sexual activity – twice or thrice & that’s all!
With males ejaculating 13% of their body weight with each tryst, that necessarily limits the number of times they can have sex in one lifetime. No one knows for sure, but cabbage white butterflies are thought to have sex two or three times. They start to produce smaller spermatophores and break down their flight muscles and internal organs. “Elderly males actually digest their own innards to fund the construction of their giant ejaculates.” (Yong, 2017)
A strange biological feature makes it easier to count and know how many times a female cabbage white butterfly mates in a lifetime. The females digest some but not all of the spermatophore received from the male; each female carries a husk of the spermatophores from all her past sexual encounters inside her genitals. These can be counted if you dissect a female butterfly, which is how it is known that most females mate two or three times (with some outliers able to manage up to six matings). (Yong, 2017)
stranger stuff still!
The male and female butterflies don’t just ‘mate’ in any sense we would understand. The male doesn’t implant the spermatophore into the female but rather – builds it inside her body! Truly alien sex stuff! Yong (2017) writes that “Using separate glands in his aedeagus—a penis-like organ—he first transfers the tough outer envelope, inflates it with the nutritious inner core, and caps the whole lot with sperm.” Bizarro!
What’s more, the females participate in this and inject digestive proteins into this construction. This is because the female won’t mate again until the nutrient pack in the spermatophore has been dissolved, at which point she will lay the eggs, and then seek out another mate and repeat the process to lay more eggs.
What we don’t quite know is all the ins & outs of how female butterflies choose their mates. Clearly there’s a lot going on – pheromones, colouring, behaviour….
So the mysteries of the sex lives of butterflies continues to promise more insights and hidden marvels. But that’s enough for today.
Castro, J (2015), Animal Sex_ How Butterflies Do It _ Live Science
Yong, Ed (2017). This Common Butterfly Has an Extraordinary Sex Life – The Atlantic