Ecological stowaways. That is how invasive species were described many years ago by American ecologist Aldo Leopold. Nowadays, invasive species are recognised as one of the most significant threats to biological diversity in the world. As it turns out, it is not just the Sosnowsky's hogweed, introduced during the Soviet era, or the slimy Spanish slug in the garden lawn, but a far wider group of plants and animals that are aggressively carving out their place in the Latvian wild and are proving difficult for humans to control, displacing the native "inhabitants" of our nature.