Without any human intervention, the Argentine ant — the world’s most invasive species — is disappearing from New Zealand. The alien ant arrived in New Zealand in 1990 and has since marched across our two main islands. Dealing with the pest was projected to cost $68 million per year. Perhaps no longer. Phil Lester and colleagues at Victoria University say that alien ant colonies in 60 locations are collapsing on their own. Lester thinks low genetic diversity, which is associated with reduced disease resistance, is the most likely reason for the ant’s demise. Research published in Insectes Sociaux in 2009 stated that the “enormous extent of this population is paralleled only by human society”, and had probably been spread and maintained by human travel.