You’ve got two life forms who are hermaphrodites, and they’re having sex. But how do you describe it accurately, without calling on human-centric terms like “male” and “female” or “penis” and “vagina”? It’s one of those rare writing questions that comes up for both scientists and science fiction writers. In the interests of advancing the state of the art in scientific sex writing, we’ve got a handy guide to the ins and outs of hermaphrodite sex.

There are a lot of good reasons to describe hermaphrodite sex accurately. You might want to present correct scientific information, as unclouded by human bias as possible. Or you might want to write a science fiction story about hermaphrodite aliens that allows your reader to truly understand what it would mean to have sex without having two sexes. Either way, we’ve got some pitfalls to avoid and a few pro tips for your next foray into hermaphroditism.



What Is A Hermaphrodite?

There are a number of animals on Earth who are simultaneous hermaphrodites. That means they possess both the ability to fertilize another organism, and to become pregnant themselves. Some are sequential hermaphrodites, who can transform from one sex to the other during their lifetimes, often in response to environmental cues. The clownfish is one such species where males become females — and yes, that means Nemo was destined to become a woman. There are also animals like the nematode Caenorhabditis elegans who have two sexes, but one of those sexes is male and the other is hermaphroditic.

Also, just to be clear, I am using “sex” to refer to biological sex, and “gender” to refer to social roles among humans.

The term “hermaphrodite” is occasionally and incorrectly applied to humans. Humans are not a hermaphrodite species. There are a wide range of scenarios, from genital variation to genetic abnormalities, that can result in humans born with traits of both sexes. These people are called intersex, not hermaphrodites. Seriously, if you call a human a hermaphrodite, I’m going to spank you with an anatomy textbook.

Many animals, especially hermaphrodites, have genitals that are so different from humans’ that calling them “penises” and “vaginas” is metaphorical at best and downright incorrect at worst. Many hermaphrodites, like sea slugs and leeches, impregnate each other via hypodermic injection in a process scientists have (in their human-centric way) dubbed “traumatic insemination.” For example, every leech has a special area of thick skin called a clitellum. During sex, leeches line their clitella up. Then they shoot spermatophores, or special packages of sperm, into each other’s clitellum. The spermatophore drills into the skin and releases its payload inside the leech. Calling the clitellum a vagina is an insult to vaginas and clitella everywhere.


Sea Slug Gender Trouble

Biologist Rolanda Lange and colleagues recently published an article in PLoS One about the sex lives of hermaphroditic sea slugs. It got a lot of play in the media, mostly because the whole traumatic insemination thing allowed a lot of journalists to make 50 Shades of Grey jokes about how the ladies like it rough. The problem? These jokes have their basis in a fundamental misunderstanding about sea slugs. There no “ladies” among these hermaphrodites.

This misunderstanding, however, originated with the scientific paper itself. Lange and colleagues chose to divide sea slugs up into three categories, based on how they were having sex at the time: male, female, and mutual. When I asked Lange why she chose to describe hermaphrodites as males and females, she said via e-mail:

Hermaphrodites typically possess male organs, which produce, store and transfer sperm, which can then be referred to as the ‘male’ part of this organism. At the same time they also have organs to produce and store eggs and receive sperm; which can then be referred as the ‘female’ part of this animal. A hermaphrodite can act in certain manners that are more attributable to the male part and vice versa. When they for instance try to insert their penis into their partner, but avoid the others’ penis being inserted, you could say that they are trying to pursue their male function.

Lange and many other scientists face a difficult challenge when writing about hermaphrodite sex. It’s usually easier to call on well-worn categories like male and female when you’re doing a bunch of research, much the same way electricians will refer to male and female plugs without meaning anything by it.

Ursula Le Guin writes about this challenge in her famous novel The Left Hand of Darkness, which is about an anthropologist sent to study a planet of humanoid hermaphrodites. These people are sexless most of the time, but when they go into “kemmer” (basically an alien version of going into heat) they develop sexual organs that may be male or female depending entirely on the the situation. Our hero can’t figure out a way to describe people who have no gender, so he starts secretly assigning male and female designations to everyone he meets — based entirely on his gender stereotypes of women and men. All of his tidy gender assignments get turned on their heads, of course, when his brave, “manly” companion turns into a woman who is aching to have sex with him. Le Guin’s point is that humans want to project their gender norms onto everything, even where there is no gender or sex as we know it. We can’t even describe an alien species without trying to shove its members into male and female boxes.

To return to Lange’s sea slug research for a moment, the problem with her research team’s description is that these creatures are not females or males. Even when they are inseminated, they are still hermaphrodites. To put this in more human terms, calling a hermaphrodite “female” when it is being penetrated during sex is kind of like calling a gay man “female” when he’s penetrated during sex. It’s a scientifically incorrect description of a sex act. Just because a sea slug possesses eggs doesn’t make it any more female than a gay man is. Both our hermaphrodite sea slug and our gay man already have sexes, and neither is female. It would have been far more accurate for Lange and her colleagues to divide up their sea slugs into penetrated, penetrating, and mutual.

When You Fight With Your Penis, Who Loses?

In this video, you can see two lovely hermaphrodite flatworms engaging in what is fondly known as “penis fencing” among scientists. Recently, a biologist told me that she was taught in college about flatworm sex as a “conflict where they fence with their penises and the loser gets stabbed, and is therefore female.” This is another example of the same problem we saw with the sea slugs, where the penetrated party is dubbed female. But what’s even more interesting is the way some scientists choose to characterize this sex act as a “fight” where there’s a loser who just happens to always be female.

Obviously there is a lot wrong with this description. First of all, both of these flatworms are hermaphrodites. They don’t have penises, but organs that deliver sperm. Also, the flatworm who gets pregnant is hardly a “loser” — every insemination is a form of “winning” for both parties, since both will now pass along their genetic material to a new generation. It’s likely that the first scientist who called this mating act a “fight” was projecting human gender stereotypes just like our character in Left Hand of Darkness did. If penises are drawn, it must be a fight! Because men have penises and they fight! Right.

. . . And women are always losers in any sexual situation, right? Right. Except it’s wrong.

Beyond Male and Female

OK, we’ve seen what happens when we try to apply our human biases and sex characteristics onto hermaphrodites. So how do we describe hermaphrodite sex in a neutral way? One possibility is what I suggested earlier, in regards to sea slugs, which is to talk about the animal who is penetrated and the animal who is penetrating. Another possibility is to focus entirely on who is fertilizing and who is being fertilized, without reference to male and female.

Photo of Ophryotroeha diadema by Annette Bergter.

A great example is how Gabriella Sella describes worm sex in the abstract for a paper in Animal Behavior:

Ophryotroeha diadema is a simultaneous hermaphrodite polychaete worm . . . Its mating behaviour was investigated in order to elucidate the relationships between mating system and reproductive biology. A genetically determined yellow or white coloration of the eggs and body walls made it possible to distinguish the egg releaser from the fertilizer. The following main features of the mating system were established. Pairs are formed preferentially between simultaneous hermaphrodites, one partner releasing eggs and the other fertilizing them . . . The partners attain spawning synchronization by means of close mutual contact during a fairly time-consuming courtship. Partners regularly alternate sex roles, usually with the same partner more than once in succession. Both partners care for their eggs and protect cocoons of neglected eggs spawned by other pairs.

Note that Sella talks about “egg releasers” instead of females, and “fertilizer” instead of males. Now we have a better picture of hermaphrodite sex as such, rather than viewed through the distorting lens of gender.

In a paper on sea hares, Steven Pennings refers to “sperm donor or receiver” during hermaphrodite sex, which is another good way to talk about these creatures. Contrast Penning’s description with the one in this National Geographic video, where the narrator insists on saying the sea hares are “acting solely as females” when they are “mounted by” other sea hares. What’s particularly sad is that this incorrect male/female designation basically erases what’s really happening in this video — which is a lot more interesting and complex than any male/female combination I’ve ever seen.


An interesting example of how to describe hermaphrodite sex crops up in John Varley’s space opera Wizard. The book deals in part with an alien species called the Titanides whose members have three sets of genitals and can have sex in several different combinations with multiple partners. Though they are hermaphrodites, these aliens identify as the sex of their “front” genitals, so Varley uses that cultural detail to solve the problem of having to call all these creatures “it.” The best part, however, is that their sex lives can only be explained via an elaborate diagram showing all the possible fertilization combinations (the diagram is included with most editions of the book). In Titanide society, reproduction is only permitted if the cyborg who runs their world approves of their mating diagram, so Titanides strive to create the best combination of genitals in a structure they hope will be appealing. Basically, Varley chooses to describe hermaphrodite sex in the most granular, detailed way possible, by using this chart.

Another route you can go when writing about hermaphrodite sex in science fiction is to invent a new set of genitals, and a new sex, for your aliens. That’s what Octavia Butler did for her hermaphrodite ooloi in the Lilith’s Brood series. The ooloi mate with one female and one male at the same time, connecting to both using tentacles. Once connected, the ooloi can inject the male and female with chemicals that induce pleasure, and can withdraw genetic material from both, mix them inside its body, and produce an offspring that combines genetic material from all three partners.

In each of these cases, ranging from scientific papers to science fiction novels, the authors strive to explain sex without two sexes. Doing this truly requires you as a writer to put yourself into an alien mindset. And that can be hard to do, especially when it’s so tempting to make dirty human jokes using hermaphrodite sex. Just look at this video of hermaphrodite barnacles having sex using an ultra-long organ for insemination and try not to see a giant penis zooming into a sea vagina.

But the fact is, just because it’s hard to shed your human preconceptions doesn’t mean you shouldn’t do it. The result will be better scientific writing, and hard science fiction that actually draws your reader into a world he or she may never have imagined before. And that, ultimately, is the goal of all science — to explore what is unknown, and understand it to the best of our ability without bias or prejudice.