When I first encountered a female changeling—here defined by the gender of their preferred pony form, for reasons that will be explained shortly—I found myself quite confused. Based on my initial observations, there were absolutely no physical differences between her and the male changelings I had already seen. All civilized life forms in Equestria, from Diamond Dogs and Minotaurs to Ponies and Griffons, exhibit at least some form of readily apparent sexual dimorphism, but these changelings seemed to have none. Fortunately, unlike with the mystery of how their disguises work, the female changeling I had met was able to fully explain the situation to me.
Changelings both do and do not have genders.
It it easiest to start with the 'do not' side of this seemingly paradoxical statement. This is the biological side of things. All changelings possess organs resembling both male and female pony reproductive organs, which ensures that their disguise is completely flawless regardless of what gender their pony form is. One might be inclined to classify them as hermaphroditic based on this information. This would be an accurate classification, except for the important fact that changelings are also completely sterile. These organs are mere replicas of the ones found in actual mares and stallions. They're not even any more sensitive to physical stimulation than the rest of their body.* Because of their complete inability to reproduce, changelings cannot be said to have such a thing as gender from a biological standpoint.
As an interesting side note, I learned that because of this, changelings who enter into long term relationships with ponies tend to prefer same sex partners. This way, their sterility is much less likely to become an issue, or to even be brought up, period. This is hardly a strict rule, however.
Now, as mentioned above, changelings both do and do not have genders. The biological viewpoint has provided the 'do not' side of this statement. For the 'do' side of things, we must now turn to the psychological viewpoint.
Changelings do possess a sense of gender identity. In laypony's terms, this means that changelings mentally identify themselves as either male or female, despite not actually having a biological gender. This identity develops during their formative years and is reflected in the gender of their preferred pony form. I found this concept confusing at first, but upon further thought, I could see how it was a necessary adaptation for them to develop. After all, how could a species with absolutely no concept of gender manage to secretly integrate themselves into pony society as flawlessly as they have?
It is important to note that the strength of a changeling's gender identity varies between hives. For instance, changelings from some hives will go their whole lives as only a single gender of pony, whereas changelings from other hives are perfectly comfortable with taking the form of a mare one day and a stallion the next. I also later learned that there is a strong correlation between the strength of a changeling's gender identity and how attached they are to a single pony identity. To continue the above example, the first changeling will likely only have a single pony identity that they ever use, while the second changeling is more likely to have a hoofful of different identities that they regularly swap between.
I was curious if changelings queens were equipped the same way, both physically and psychologically. Unfortunately, the female changeling who was explaining all of this to me did not know, and there was no way that I would ever ask such a personal question to a changeling queen myself. This will simply have to remain unknown for the time being.
Learning that changelings were completely sterile brought up another vital question; how do they reproduce? The female changeling was able to inform me that, unsurprisingly, the changeling queen is solely responsible for reproduction, but that she didn't know the specifics behind it. I was once again forced to turn to the same changeling queen that had been such a huge help in helping me learn how their disguises work.
Here, more than anywhere else, does the changeling’s insectile nature become apparent.
Specifically, the horn of a changeling queen, in addition to channeling magical energies, is also an ovipositor. It is used to inject what are essentially very small embryos into cocoons filled with emorphic gel, with one egg per cocoon. These cocoons are carefully nurtured for a few months, at which point the changelings are old enough to move about on their own and are released from the cocoon. Of course, they are only considered changeling nymphs at this point. It takes another eight to twelve years for them to reach maturity, at which point they can create their first pony identity and leave the hive to enter pony society and begin gathering emotional energy.
The cocoon phase is the most vital portion of a changeling’s development. The emorphic gel is infused with as much emotional energy as it can possibly hold, and this is almost always enough to last the few months that it takes for the larval changeling to leave the cocoon. The types of emotions provided to the changeling play a vital role in determining what the changeling will be like when they are older. The only restriction is that the majority of the emotional energy provided must be of the preferred emotion of their hive. The rest of the emorphic gel’s capacity is then typically split between two other emotions. There are no real rules as to what other emotions are added, although, at least with this particular hive, they try to never repeat the same mixture of emotions twice.
The cocoon phase is also what differentiates regular changelings from changeling queens. A changeling queen starts out life just like any other changeling, as an embryo deposited into a cocoon. The difference is in the emotional energy mixture that their cocoon is infused with. Instead of only three types of emotions total, a changeling queen cocoon is packed with as many different types of emotions as the hive can possibly provide it. If the new changeling queen is meant to replace the old one, then the preferred emotion of that hive will still represent the majority of energy in the mix. If she is instead meant to go and found a new hive, then it will instead be a much more even mix between all the emotions present.
Caring for a changeling queen cocoon is a very tricky and delicate process that requires the current queen herself to personally oversee. Emorphic gel is really only meant to hold a single type of emotion for any extended period of time. It can handle more than one type of emotion for shorter periods of time, as with the three emotion mixture used for regular changelings, but any more than that and it starts to become increasingly unstable. In addition to this, changeling queens also remain in the cocoon phase for much longer than regular changelings. Two to three years is not an uncommon time span for this phase. Also unlike regular changelings, the larval queen uses up their provided emotional energy much faster. Their emorphic gel needs to be recharged with more emotional energy every few weeks, and not necessarily with the same mixture of emotions.
Needless to say, raising a new queen is a tremendous expense of time and energy for the entire hive.
I have to admit, I found it surprising to learn that the entire hive’s survival lies solely with the changeling queen. It seems to be a very fragile system; if anything were to happen to the queen, the entire hive would slowly die off. And unlike with actual insects that use similar systems, the loss of an entire changeling hive would be a serious blow to the entire species. However, I have been assured that changeling queens, being creatures with such high levels of internal magical energy, are very hard to permanently injure or kill. They are very similar to the Princesses in this respect. Also like the Princesses, they are extremely long lived creatures. From what I have been able to learn, even the youngest current changeling queen is over three hundred years old. Because of these factors, it is actually a very rare event for a hive to give birth to a new changeling queen.
*I have been assured that being able to directly feel the emotions of their partner more than makes up for any lack of physical stimulation.