Just had cool dream, mostly a nightmare that woke me up multiple times on a loop during the night, but it was so cool I forced myself to back to the same nightmare after falling a sleep again. The nightmare was mostly inspired by the anime Kiseiju(Parasyte)

One night, tiny worm-like aliens with drill-like heads called Parasites arrive on Earth, taking over the brains of their hosts by entering through their ears or noses. One Parasite attempts to crawl into Shinichi's nose while he sleeps, but fails as Shinichi wakes up, and enters his body by burrowing into his arm instead. In the Japanese version, it takes over his right hand and is named Migi, after the Japanese word for 'right'. Because Shinichi was able to prevent Migi from traveling further up into his brain, both beings retain their separate intellects and personalities. As the duo encounters other Parasites, they capitalize on their strange situation and gradually form a strong bond, working together to survive. This gives them an edge in battling other Parasites who frequently attack the pair upon realization that Shinichi's human brain is still intact. Shinichi feels compelled to fight other Parasites, who devour other members of the species they infect as food, while enlisting Migi's help.

The plot of the dream doesn't matter, but there's something that wasn't in the anime or manga, those parasites' can choose their abilities before they get too old, abilities which reshape their biology permanently but can be hidden when they mimic humans or other animals.

The abilities are varied but I'm going to give only a few examples:

  • Releasing something in the air that makes everyone in a certain range unable to perceive the parasites' in any way, making themselves virtually invisible if close enough.

  • Infecting others with specialized vermin that makes them slaves to the command of the parasites' which created them.

  • Fertility, being able to create other parasites' either sexually or asexually.

After choosing one specific ability, the parasites will be proficient in only that particular ability but then they can still chose other abilities, but the secondary abilities will be so weakened that they are almost useless or incredibly situation dependent.

For example if one chose the ability to not be perceived as secondary, that ability will only work a certain percentage of times and in a smaller range as opposed to working 100% of the times and in ranges as wide as 25 meters or 82 feet.

I just wanna ask if there are real examples of animals voluntarily (voluntary as in not automatic) choosing abilities/castes/roles before they reach adulthood I'm pretty sure a lot of animals can choose their sex, but this is not what I'm looking for.

  • 3
    $\begingroup$ "examples of animals voluntarily choosing...." presupposes a degree of free-will and intelligence that we generally only attribute to humans. Is that quite what you meant to ask? $\endgroup$ Feb 3, 2022 at 13:22
  • $\begingroup$ @EveninginGethsemane I've seen videos of ducks choosing between different foods, which means that even animals with small brains can make ''voluntary'' choices $\endgroup$
    – user89947
    Feb 3, 2022 at 13:24
  • 1
    $\begingroup$ Not sure this qualifies (hence a comment) but some insects will engineer their progeny for a role. For example bees can force some eggs to come out as male bees or female bees. The new bee didn't voluntarily choose but the older ones did (well, more by instinct but it wasn't random). $\endgroup$
    – VLAZ
    Feb 3, 2022 at 14:09
  • 2
    $\begingroup$ @VLAZ: And mama crocodiles can choose if their eggs will produce boy crocodiles or girl crocodiles. $\endgroup$
    – AlexP
    Feb 3, 2022 at 17:23
  • 2
    $\begingroup$ @Daron: "Worldbuilding is not for asking about real animals": Oh yes it is. Nothing better than real world example to imitate. Omnis ars naturae imitatio est. $\endgroup$
    – AlexP
    Feb 3, 2022 at 17:51

3 Answers 3


Royal Jelly.

enter image description here

Female Bee grubs can turn into a queen or a worker. Which is which is not decided from birth. It depends on the amount of food the grub receives before it pupates. If it gets a lot (usually in the form of royal jelly) then it emerges from the cocoon as a sexually mature Queen bee. Otherwise it becomes a sterile worker.

Question: What about winged males and drones?

Grubs have to be fed by other bees. They do not choose what to become. But if your species have larval stages that can feed itself, and smart enough to choose then they can decide how much to eat and what to become.

It is conceivable they have two or more types of food and this allows more different castes.

  • 1
    $\begingroup$ Queen bees can lay either fertilized eggs (which develop into workers or queens, depending on what food is given to the larvae), or unfertilized eggs (which develop into males aka drones). (Male bees are called drones. They all have wings.) $\endgroup$
    – AlexP
    Feb 3, 2022 at 17:57
  • $\begingroup$ @AlexP Oh you're right. There are no such thing as sterile males. I must be thinking of ants. $\endgroup$
    – Daron
    Feb 3, 2022 at 18:00
  • $\begingroup$ Ant take this much farther with many more castes with different triggers, identical genetics can produce different castes just depending on trigger, some of those triggers can even be how many caste X, Y, and Z said ant has encountered. sciencedaily.com/releases/2008/10/…. $\endgroup$
    – John
    Feb 3, 2022 at 23:57

There are no know cases of eusocial animals in which an immature individual chooses their future caste for themselves. Such a system is unlikely to evolve, because eusociality with caste differentiation evolves to solve a variety of evolutionary problems, and for the individual to choose their own caste could easily lead to an imbalance in the necessary numbers of individuals in the various castes.

From the individual's point of view, it would always be best to be a breeder, however, without other castes or any way to influence how many mature, the breeders may not have enough assistants to allow them to survive.

Rather, juvenile eusocial creatures have their caste imposed upon them by their elders in response to the needs of their community, ensuring that enough of each caste are produced in order to meet the needs of the group.


All animals go through processes on which they have no control of their own. A larva will become a pupa and then butterfly naturally. It cannot choose to remain larva or jump to butterfly phase without being pupa. Their abilities are not by choice but by instinct.


You must log in to answer this question.