What would a eusocial species of lepidopterans look like?

Question

I am writing a science-fiction story that takes place some million years in a future Earth. There is a species of lepidopterans that evolved to become eusocial. They are my gnomes. My species is a sequential omnivore: caterpillars eat other insects, and adults are nectarivores, but queens need some blood in order to produce a huge quantity of eggs. Also, there are up to five queens in each colony. Queens need to be constantly with a king in order to reproduce (so, their way of reproducing is halfway between ants and termites, which are infamous to be mortal rivals). The castes are (from highest to lowest): royal couple(s) (the queen and the king or the queens and the kings), vice-royal couples (princesses and princes), soldiers, and workers. Colonies range from 10,000 to ten millions members. Colonies are formed in trees. Finally, my species lives in temperate and subtropical regions of the northern hemisphere, North America to be exact, and is a descendant of the harvester (Feniseca tarquinius).

I know that most eusocial insect species (ants, eusocial bees, and eusocial wasps) are hymenopterans. That said, some are blattopterans (termites). Apparently, there is at least one species of eusocial coleopterans.

Genetically speaking, lepidopterans, dipterans, trichopterans, nannomecopterans, mecopterans, neomecopterans, and siphonapterans form the Panorpida superorder. Also, most Panorpida species are solitary when they become adults.

So, I wonder how could lepidopterans evolve to be eusocial.

Answer 1

To understand why something would become eusocial, you first need to understand what is eusociality (reference enter link description here) and why lepidopterans are not presently.

1. Cooperative brood care- in many species, such as ants and bees, the young require special care to ensure their survival that takes dedicated effort over long periods of time. Butterflies, presently, do not need much care for their young. Eggs are laid, unprotected, and the parents then go off and die. The larvae then hatches and treks off on its own. This aspect of reproduction would need to change. If the physiology were to change, say become more complex, requiring more extensive care to survive, the species that stick around to care for the larvae would succeed to continue to evolve.

2. Overlapping generations within the colony- Presently, butterflies, in their final form, are only around for a few days or weeks and die soon after laying eggs. If the species became more complex in some way, with a more fragile larvae form, this point would come naturally to the species or else it goes extinct real quick.

3. Division of labor- Again, with the organism becoming more complex, with a fragile larvae state, this would have to occur for the species to survive. Caring for young requires a lot of time and energy. Without dedicated drones to care for the young, provide colony maintenance and gathering food, the colony as a whole would collapse. This may also create the brooding queen caste as a division of labor.

Now, to make the leap from a robust larvae, such as a caterpillar to a helpless one, such as a bee's larvae is huge and require many evolutional changes to occur to prevent this being a genetic dead end.

Maybe the easiest way to get over this hurdle is to first have butterflies live well beyond their initial breeding period, maybe even be able to breed several times before dying off. This could allow the species to develop more complexity, extending the post hatching development period. This would cause an evolutionary feedback loop encouraging development of eusocial behaviors.

To extend the life span naturally, your species could develop in an interglaciation period in a tropical climate in order to survive the winter. Then maybe the required evolutionary changes could occur

Answer 2

This has been an interesting thought experiment, below are four semi-solutions which you can possibly build off of.

They evolved that way

"takes place some million years in a future Earth" Millions of years is a long time especially more so for species with a shorter reproductive cycle. Humans, in our current iteration, have only been around for some 200k years. There could have been an outside event that caused non eusocial butterflies to just die or get eaten or not be able to reproduce and only the eusocial mutants lived to pass on their genes. It does make sense from a half-logical point of view since animals that that form social hierarchies seems to do better than animals that lone-wolf.

Some eusocial species evolved to look like butterflies

Convergent evolution is thing after all, look at fish and whale or the Crab Master Race (https://en.wikipedia.org/wiki/Carcinisation) There could be somethings so naturally desirable in the form of a butterfly that some semi-similar already-eusocial animal evolved into it. Maybe for example the atmosphere changed composition and they now need larger wings to still fly. This would probably be a better route if physical body evolution was easier than biological brain evolution, which could be true since in one generations, moths were able to "turn" black in response to the industrial revolution (https://www.bbc.com/news/science-environment-36424768)

Genetically edited

In a thousand years humans would have perfected CRISPR technology and would have tested it on a variety of animals before doing it on themselves. These animals, once given the initial push, escape from the lab or are just let loose by humans and go out into the real world. Some insta die to the bad hand they are dealt but others continue to evolve and adapt.

It just happened

"writing a science-fiction story" This is a sci-fi story, not a Nobel Prize in Biology winning thesis paper. Use the old "nuclear waste from extinct humans" trick. I didn't know what half the words in your questions meant until I googled them and I still don't really know what they mean. It is not inconceivable to the general public that bugs just do bug things and some traits of bugs and manifest themselves in other unrelated bugs.