TLDR: Build your leaf drop off next to the nest entrance and close to your nursery tiles.

They won't be able to replace their losses.

The AI will make a strong response, but if you can beat that wave down, you will be half way to breaking the AI economy. When your nest is strong enough you can make large raids on the AI harvesting operations, killing large numbers of their workers. Yes, the nest does spawn some super-majors for free, but the rest of the ants function like yours do. If they run low on food they will loose much of their capacity to harvest and wage war. Next, the AI nest uses resources and builds workers, soldiers etc. This setup ensures you process leaves as fast as possible which is key for 3.1 To maximize this system you should build the leaf storage as close as possible to the nest entrance, build 25 or so worker tiles immediately next to the storage and then build your refuse dump a few tiles away. When raw leaves are dropped off, the minum workers take the pieces to the nearest free nursery. There's a specific way of building a leaf-cutter nest which massively increases your economy. There are two key things to know about 3.1 before going in, otherwise you will likely fall behind the AI. If you do this once or twice, you should overtake them in numbers easily. Kill returning workers, grab their leaves, retreat, repeat. Once you have a decent force, start attacking enemy supply lines. But you can keep one big group seperated as a 'military' to hunt predators, or even go bother the other colony. I mix them into my other groups as defense. Yet again, organisation depends on your strategy. Once you have a dozen, ideally more harvester ants, you can start getting some Majoris. Try focusing on the area north of your starting point, try to both harvest for yourself and deny the enemy easy access to leaves. And then 2 groups of mixed ants that clear out areas of enemies to get at more leaves.

I keep 1 group that just consists of small workers which I use to 'clean' up almost empty areas. How you organize now depends on the strategy you want to employ. Once you have around 20 small workers (Your mileage may vary) start working on proper worker ants. Split them into 2 or even 3 groups, micro manage to ensure that they do not run into predators repeatedly, and pick the immediate area around the nest clean. Get a bunch of small workers in the beginning.

Empire of the undergrowth first mission