Stephen Dalton / Harlequin ladybird (Harmonia axyridis) in flight, invasive species, England, UK. March.

Sam Hobson / Rose-ringed / ring-necked parakeets (Psittacula krameri) in flight on way to roost in an urban cemetery, London, UK, January. Finalist in the Birds category, Wildlife Photographer of the Year Awards (...

Claudio Contreras / Black Rat (Rattus rattus) young. Introduced species on Maria Magdalena Island, Marias Islands Biosphere Reserve, Gulf of California, Mexico, September.

Bert Willaert / Composite image of American fish species introduced to Europe: Pumpkinseed sunfish (Lepomis gibbosus, left), Brown bullhead (Ameiurus nebulosus, right) and Eastern mudminnow (Umbra pygmaea, under), ph...

Rob Jordan / 2020VISION / Signal crayfish (Pacifastacus leniusculus) in a defensive posture after being caught by The Tweed Foundation monitoring the species population and spread on the River Till, Northumberland, England, UK...

Rob Jordan / 2020VISION / Signal crayfish (Pacifastacus leniusculus) in a defensive posture after being caught by The Tweed Foundation monitoring the species population and spread on the River Till, Northumberland, England, UK...

Roberto Rinaldi / Yellow fan coral / Seafan (Paramuricea clavata) amongst mass of invasive algae (Caulerpa taxifolia) with Rainbow wrasse fish (Coris julis), Strait of Messina, Southern Italy

Jerry Monkman / Nature Conservancy employees cutting back Japanese knotweed (Fallopia japonica) in an invasive species eradication effort on the TNC's Silverweed Seep preserve in Plainfield, New Hampshire, USA.

Michael Durham / Red Imported Fire Ant (Solenopsis invicta), also known as RIFA, worker portrait, highly invasive introduced species, Texas

Konrad Wothe / Dandelion (Taraxacum officinale) ready to release its seeds, Germany, introduced into North America as a salad green now is invasive weed

Nigel Cattlin / Spanish bluebell (Hyacinthoides hispanica) cross section of bulb with leaf and root development. Cultivated in garden. January.

Nigel Cattlin / Spanish bluebell (Hyacinthoides hispanica) bulb with leaf and root development in late winter