Fungi play an important part in the lives of leaf cutting ants. For when a young queen leaves her colony to start a new one, she takes with her some of her mothers chewed up leaves. It is not the leaves that matter so, but what is on them, fungi.
After a queen mates and finds a home, she cultivates her new garden carefully, alongside her first larvae. If this batch of fungi fails her colony will have no chance of survival. If her garden succeeds, the gray springy heap of fungi will grow long hyphae, which will eventually form swollen tips.
By this time some workers may have become adults. They will harvest these tips as food, and weed out objectionable varieties of fungus.
Meanwhile the fungi are being pampered. They are fertilized with ant dung and provided chewed leaves as a food source.
In conclusion, fungi unmistakably are essential to leaf cutting ants.