Leafcutter ants belong to the tribe Attini which is more commonly known as the attine or fungus-growing ants. These ants collect plant material and feed it to a symbiotic fungus, which they use as the sole food source for their larvae. Although attine ants started cultivating fungi 50-60 million years ago, only the most highly evolved genera Acromyrmex and Atta actively cut leaves to feed to their fungus, and this branch of the attines are known as the leafcutter ants.
Check out this video from The Royal Society of one of our Postdoctoral Research Associates Phil Leftwich, sharing 3 amazing facts about ants:
Leafcutter ants create a warm, humid environment to grow their fungus and this is attractive to many other parasitic and disease-causing microbes. To protect their food source the worker ants constantly patrol their fungus gardens and remove unwanted bacteria and fungi. Many attine ants, including Acromyrmex, also grow symbiotic filamentous actinobacteria on the outside of their bodies and use the antibiotics made by these actinobacteria to kill the unwanted microbes. When an attine colony produces new queens they take a piece of the fungus and some of the actinobacteria called Pseudonocardia with them to start their new colonies. This is called vertical transmission because the fungal and bacterial symbionts pass directly from generation to generation.
Attine ants have most likely been using natural product antibiotics for as long as they have been farming fungi, i.e. more than 50 million years. Compare this with humans which evolved no more than 400,000 years ago, developed agriculture 10,000 years ago and discovered the first natural product antibiotic less than 100 years ago and the achievements and civilizations of the attine ants is truly staggering.
For more information take a look at this great animation written by Kathryn Machin and made by students at Manchester University: