Not only can ants be used as pesticide - in some cases they also act as a herbicide and kill weeds and other plants that compete with their host tree: <a href="http:&#x2F;&#x2F;www.nature.com&#x2F;nature&#x2F;journal&#x2F;v437&#x2F;n7058&#x2F;full&#x2F;437495a.html" rel="nofollow">http:&#x2F;&#x2F;www.nature.com&#x2F;nature&#x2F;journal&#x2F;v437&#x2F;n7058&#x2F;full&#x2F;437495a...</a> . Probably not useful for farming, but still cool.