What natural factors could possibly push a species of eusocial insects to become intelligent?

Personally, I've been brainstorming a race of haplo-diploidal eusocial mammalian-like humanoid aliens who, biologically, would be divided among the following 3 classes based on sex chromosome count (with cultural titles inspired by feudal European castes):

• Single X chromosome: Serfs, infertile workers with a child-like intelligence, whose main purpose is to support the noble mother that gave birth to them, along with the colony that they, along with their mother and siblings, including other nobles that their mother might've given birth to, live and dwell within (which would likely be about the size of a small village of a hundred or so members). However, despite their low intelligence, and their instinctual imperative to keep their colony alive and reproducing, even the serfs within the colony are quite capable of independent thought and talent, and with it, are quite capable of performing not just dumb labor (including tending to their younger siblings like babysitters or nannies), but also skilled, and even creative, labor tasks, much like the ones found within human civilization, from farmers, carpenters, and electricians, to soldiers, and even scientists!

• XY chromosome pair: Princes, male drones whose sole purpose is to inseminate whatever female nobles are nearby (especially those nobles whom haven't been inseminated by a prince as of yet), with at least one of these nobles being chosen by the prince (usually, though not necessarily always) to become a princess that's capable of bearing their sons through continuous intercourse (to stimulate their noble mate's growth into a form that would allow their male princely offspring to properly gestate without being aborted via miscarriage). A prince who has fathered many princes and princesses is often referred to as a king, and often possesses widespread social influence comparable to one.

• XX chromosome pair: Collectively called nobles or ladies (with different sub-classes according to physiological development), they're akin to insect hive queens, though unlike them, while all nobles (with a few rare exceptions) are able to lay eggs that hatch into serfs (without requiring sexual intercourse, a.k.a. asexual reproduction), not all of these nobles are able to give birth to other nobles, and only a select few are able to give birth to princes (though all nobles have the potential to give birth to both nobles and princes, albeit a potential that can only be awakened depending on how often they've had intercourse with a prince). All nobles possess two wombs, one that's designed to continuously gestate the eggs that the nobles lay, which then hatch into serfs, and another womb, where egg cells are waiting to be fertilized by a prince's sperm in order to turn into zygotes that gradually transform into infant nobles or princes, which gestate at a slower rate, and are born live (like mammals and humans).

The noble class could be sub-divided into the following sub-classes:

--- Maidens: Taskmaster-like nobles who can only give birth to serfs, and can only morph into the next sub-caste by being inseminated by a drone. (Even once will do, since the drone's sperm would then be carried and preserved within one of the noble's 2 wombs.) They typically watch over the serfs that they give birth to, much like the mother of a household, and also often socialize with other nobles, especially their parents and siblings.

--- Mistresses: Insemination by a drone triggers a hormonal reaction within a maiden's body that not only supplies her with semen, but also gradually transforms her into a mistress, a minister-like noble that, in addition to laying eggs that hatch into serfs, gains the ability to give birth to infant maidens, though still lacks the ability to gestate princes (which requires constant intercourse from the prince). In addition to managing the serfs that they give birth to, they also watch over the nobles that they've given birth to, and even socialize with other nobles within a "court", a group of nobles that are centered around the prince that inseminated and fertilized them. Oftentimes, they'd watch over several nearby villages like a countess.

--- Princesses: Regular insemination by a prince would provide a mistress the ability to sustain the gestation and birth of infant princes to further spread both the prince's and noble's genes far and wide for generations to come. By then, the mistress would be considered a princess, despite the physiological changes between the two noble sub-classes being so subtle. (In fact, a princess could revert back into a mistress if their prince no longer engages in frequent intercourse with them, such as if the prince had died, or if the prince had wanted to spend more time with another noble.) Like with other nobles, these princesses would typically attempt to remain in touch with their offspring, siblings, and parents (including their prince's parents), though given how their numerous princely sons tend to flock to lands far and wide in search of nobles to mate with, they might also end up watching over vast lands, with about as much influence as the queen of a monarchy. In fact, a princess that has mothered many princes and princesses is often referred to as a queen, with widespread social influence comparable to one.

Now there may be implications towards my eusocial species' traits (such as the possibility that nearly every noble might be made into a princess if there are equal numbers of princes, resulting in a society that would mirror our modern-day monogamous society, with each prince and princess paired with eachother like husband and wife), but enough about my eusocial race's epic physiological, behavioral, and cultural lorecrafting.

One thing I'd recommend keeping in mind when designing a sentient race with large family sizes is Dunbar's Number. That is, whereas the average human can handle being within a social group that's 150 members large, you ought to ask yourself this: "How big of a social group can each member of each caste handle within their own social groups?" For my eusocial race, I'm personally going with around 150 members each, regardless of caste, so that I'd then have a system where each serf, noble, and prince would only be capable of meaningfully socializing with their immediate family members, including parents, children, siblings, and in some cases, in-laws, since they'd all likely add up to numbers that might stress their social capacity to the limit, with each member of their social group occupying various ranks within a much broader social and familial hierarchy, from the lowliest serf to potentially (though rarely) the queen and king of a vast family tree.

How the queens of your eusocial race would socially be able to handle laying around 3 million eggs per day, let alone interacting with their entourages of around 6,000 protectors, will ultimately be up to you to determine.

Most evolutionary pressures are easily solved via physical rather than mental improvements. Even situations in which a smarter animal would do better are usually solvable through other, simpler solutions, making the possibility that those solutions will arise higher; fewer mutations need to happen.

Thus while incredibly intelligent combat tactics are very useful, it's far more common to see incredibly strong animals than incredibly smart ones. A human can outsmart a gorilla, but without strong tools that take a lot of time to learn how to make, not to mention build, the gorilla can tear the human to shreds no matter how much smarter the person is. The gorilla is faster, stronger, and more terrifying.

Additionally, it is also a choice between the two; brains like ours take enormous amounts of energy to run, and we only have so much oxygen with which to run our bodies.

That said, there are some situations in which there is no substitute for intelligence. Complex social interaction is one of them. Our gorilla - let's call them Yog - might be able to kill everyone, but if their weaker sibling Mog is socially smarter than them, Mog is going to be the one who gets better status. That status can translate to better protection from other gorillas, better food, and more mates. Thus Mog is more genetically successful than Yog.

Of course, if Mog is too weak then Yog might gain dominance anyways. But those sorts of evolutionary pressures make it possible to end up with a species of Mogs.

Another evolutionary pressure that can lead to intelligence is the need to coordinate. Most insects, even social ones, do work on a solitary basis without needing to coordinate with other insects to complete tasks or accomplish goals. Even when they are working together on a single task, they are usually on an individual basis doing the exact same thing; it's just that a lot of them are doing it at once. Humans coordinate. In order to complete even tasks that we view as incredibly simple for the group, it is necessary or efficient for each individual involved to be doing something completely different from the others while being generally aware of the task as a whole. Consider cooking in a restaurant; the head chef directs each individual and may be cooking the end product, the prep cook cuts the pieces, a sous chef may be creating the necessary sauces, and yet another worker may be providing the correct dishes. They are all additionally aware of the entire recipe while they complete their task, and are generally aware of how the process is advancing.

So if you want your Vosians to be sapient, a good way to make it plausible is to ensure that:

1. There is plenty of oxygen or other energy-releasing gases or chemicals on their planet (this has the bonus of making their relatively large size more plausible),

2. Each individual must deal with complex social situations, and

3. The Vosians must coordinate complex tasks in which each individual has a different function in order to survive.

I would also like to add that in all earthbound social insects, the queen is not the leader; she is merely the reproductive organ of the colony, treated well for her necessity, but completely cut off from the functions that run the rest of the colony. Your Vosian queens are unusual in that sense. So it may be worth thinking about what makes them different.

Perhaps they are the only source of an important chemical that enables Vosians to recognize that they are from the same hive, and they withhold that chemical from those that do not do what they say. Perhaps they hold themselves hostage, threatening to hurt themselves and thus grind the colony to a reproductive and productive halt if the colony does not act in their interests. Perhaps they are simply the smartest Vosians and so queen-led societies tend to perform better. Or something else. Regardless, best of luck with your insectoid creatures. :)

Calling insects an evolutionary dead end. How dare you, sir. They just stopped getting changing cause they got it perfect way back in 70,000,000 B.C.E.

Okay, that's enough jokes. Personally, I like to think that human intelligence is a combination of tool use, a dependency on complex communication, and a need to alter the environment around them in order to survive. There are a bunch of factors involved with each of those list items, but it's good enough to use as a general checklist.

Common ants already fulfill all the requirements I mentioned, just not as extremely as you need. The only anatomical diffrence Volsians will need from ants is instead of manipulating with mandibles, the Volsians will likely have dexterous hands, tentacles, or other part that allows for the creation and use of fairly specialized tools.

The great news about this is that the Volsians have a good reason to evolve great manipulating appendages: building hives that can house a 43 billion family members (that's the number of births in a single non-queen Volsian lifetime. You might want to adjust that, cause that's simply too many mouths to feed for any level of civilization). Building such hives/towns would demand the Volsians learn to use tools, and the pressures of feeding a family would probably lead to agriculture and animal domestication as well.

All of the above is really dang complicated, so much so that it would likely demand that individual Volsians need to be actually taught to be functioning citizens/family members. After all, building a pyramid and growing a crop and organizing a city is a lot of information to be taken care of by in-born instincts. The logical solution is to have Volsians born as blank slates to they can be as taught to fulfill specific roles as the need arises. This stupid-baby-smart-adult strategy is basically what humans use, FYI.

In a nutshell, you have a bunch of mega-insects that need a lot more resources than normal insects (since their huge and numerous), so they evolved intelligence in order to get all the resources required. This should be enough to explain why they are smart, I should hope.

The only flaw with this I can see with your set up (other than the births-per-day) is Volsians communicating via dance. While it works for actual ants (with the aid of pheromones), having a complicated language based on dance would be really energy inefficient. For example, imagine if I had to dance the this entire answer post to you, conveying each word with some form of dance move. I'd probably burn a pilates class worth of calories by now.

Even if the dance-speak is as easy as sign language, the Volsians would still need a light source and a direct line of sight to say anything at all. Those are huge downsides for a developing civilization. Using sounds to speak would probably make a lot more sense.

Their development would have to be artificial as there are several problems with getting insects that big such as size limits on exoskeletons and having to develop lungs.

Now if someone wanted a drone species of self populating workers, a hive mentality is a great start. You'd engineer basic intelligence so they can understand instruction but not enough to rebel.

To overcome the size limitations of exoskeletons, new members would have to hatch virtually full size so they finish growing before the exoskeleton hardens. Now either the eggs have to much bigger or the eggs hatch to larvae which the workers feed until they becomes chrysalises.