Iberian Harvester Ants, Messor ibericus, can produce offspring of two different species, according to a new Nature study. Messor ibericus queens can produce males of Messor structor in addition to their own species. This bizarre observation is at odds with how scientists conventionally think about species, so it may prompt a rethink of these already blurry definitions.

The paper: One mother for two species via obligate cross-species cloning in ants