Yellow crazy ants (_Anoplolepis gracilipes_), or Maldive ants, are among the world's 100 most invasive species. Roman Prokhorov/iNaturalist , CC BY-NC Biological invasions occur when organisms such as animals and plants are introduced by people to regions of the world where they do not naturally occur. In these new locations, these organisms are referred to as “alien species” . Biodiversity is the variety of all living organisms on earth. It is the interconnected web of life that is a wonder to behold – it is also vital for people , providing the foundation for happy, healthy lives. Biological invasions can be severely damaging to biodiversity . Alien species interact with native species in many different ways. For example, they often compete with native species for resources such as food. This can cause declines in the abundance of native wildlife and, in some cases, the permanent loss of native species ( their global extinction ). The European fox has been introduced to Australia, where it preys on native animals. It has caused the extinction of several small mammal species. Fourni par l'auteur The number of alien species being introduced to new regions continues to rise. Hence, identifying and managing their impacts on native biodiversity is a global conservation priority. A great deal of research has been published on this topic. However, biological invasions can cause another type of impact that is far less comprehensively studied and managed. These are impacts that cause the suffering of animals. Animal welfare and sentience Animal welfare is defined by the World Organisation for Animal Health as “the physical and mental state of an animal in relation to the conditions in which it lives and dies”. Sentience is the ability to experience feelings and sensations, such as pain, fear and anxiety. It is now widely recognised that many different types of animals are sentient . In the United Kingdom, the welfare of these sentient animals is protected under the Animal Welfare (Sentience) Act 2022 . Biological invasions affect the welfare of sentient animals Biological invasions result in interactions between organisms (including plants and animals) that can severely harm the welfare of the animals involved. For example, the avian vampire fly ( Philornis downsi ) was accidentally introduced to the Galápagos Islands from South America several decades ago. It lays its eggs in the eyes of fledgling native birds. When they hatch, the larvae feed on the soft tissue around the eyes and nares (nostrils) of the birds. This causes wounds, infection and death. There are no native insects that cause these welfare impacts on the Galápagos archipelago. A dead nestling bird with enlarged nares (nostrils) caused by larvae of the avian vampire fly, which crawl inside the nares to feed on soft tissue. Andrew Katsis/Wikipedia , CC BY Cheatgrass ( Bromus tectorum ) is a highly flammable grass species that has been introduced to western USA from Eurasia. Across the Great Basin, it increases the frequency, size and intensity of wildfires, and the number of individual animals that they kill. These animals include greater sage-grouse ( Centrocercus urophasianus ) . Greater sage-grouse are burnt by wildfires caused by cheatgrass, which is a flammable alien plant species. Joegrzybowski/iNaturalist , CC BY-NC House mice ( Mus musculus ) were accidentally introduced to Gough Island in the South Atlantic Ocean by sailors in the 19th century. They attack and eat ground-nesting Tristan albatrosses ( Diomedea dabbenena ). Having evolved on the island in the absence of predators, the albatrosses are naive to the threat posed by the predatory mice – hence, they do not evade predation. While this is a biodiversity impact ( the mice have caused the albatross population to decrease ), it is also an animal welfare impact, as demonstrated by these images . House mice have also recently been recorded attacking albatrosses on Midway Atoll . Welfare impacts are poorly understood The animal welfare impacts of biological invasions are a neglected research topic. Few studies have explicitly attempted to identify and describe them. Hence, we do not have a good understanding of the extent and severity of the animal suffering they cause. Furthermore, we do not understand how this suffering occurs, which animals are most severely affected, and how best to protect them. Frameworks for biological invasions Frameworks are conceptual tools that provide standardised systems and rules which can be applied to make sense of complex processes. They can be useful for structuring data on wildlife, including data on the impacts of biological invasions. Several frameworks have been developed that assess the biodiversity impacts of biological invasions . However, no frameworks have been developed to explicitly assess their animal welfare impacts. Our research , recently published in the journal Nature Communications , introduces a new framework to assess the animal welfare impacts of biological invasions. This framework is called the Animal Welfare Impact Classification for Invasion Science (AWICIS). The AWICIS framework AWICIS assesses impacts on animals that are sentient and protected by UK animal welfare legislation. These are mainly vertebrate animals , although some invertebrate animals are also protected, including Cephalopods (octopuses, cuttlefish and squid) . AWICIS assesses welfare impacts affecting both native and alien animals. This is significant, as research on biological invasions tends to focus on impacts affecting native animals. Our framework recognises that alien animals can also suffer from welfare impacts caused by biological invasions. While biodiversity research focuses on impacts affecting the survival of species, AWICIS focuses on impacts affecting individual animals. It identifies “relative changes to the welfare of an individual animal” that are caused by a biological invasion. To do this, the framework uses five “impact severity” categories (i – v) to quantify the harm caused by a biological invasion on a given animal. It also categorises welfare impacts by type using 11 impact categories. For example, these categories include the “transmission of disease” from one animal to another, and “predation” of one animal by another. House finches have been introduced from the west coast of the USA to the east coast. They suffer from avian conjunctivitis, which they have spread to other garden birds in the state of New York, including purple martins. Avian conjunctivitis causes blindness, starvation and death. Coleen Lawlor/iNaturalist , CC BY-NC Indicators are used in animal welfare science to provide evidence of impacts affecting the welfare of animals. AWICIS uses three different indicators: The physical appearance of an animal (e.g., dead or injured animals) The behaviour of an animal (e.g., lethargic animals suffering from diseases) Measurable physiological functions that provide insights into the welfare of an animal (e.g., elevated levels of stress hormones produced by an animal). The welfare impacts of ant invasions We used AWICIS to assess the welfare impacts of ant invasions. Many different ant species have been introduced to regions of the world where they would not naturally occur. Some use acid to attack and kill animals. Red imported fire ants attacking an insect in Texas, USA. These ants are capable of killing much larger animals, including fledgling birds and hatchling turtles. evvobevvo/iNaturalist , CC BY-NC Using AWICIS we found several of these ant species to cause the most severe category of welfare impact on many types of animals. Ground nesting animals were often affected , including fledgling birds and hatchling alligators and turtles. Ants can take a long time to kill an animal, so they can cause a great deal of suffering in the process. Unfortunately, these ant species have been introduced by humans to many locations worldwide, including numerous islands and several regions of the USA. This means that their severe welfare impacts are an ongoing, global phenomenon. Hence, many animals have suffered, and many more will do so in the future as a result of our actions (introducing ants to places where they do not belong). Preventing the introduction of ants (and other organisms) to new environments is crucial if we are to stop biological invasions from causing unnecessary and severe animal welfare impacts. A more complete picture of the impacts of biological invasions It is well known that biological invasions are problematic for biodiversity – they threaten the survival of native species. The socio-economic impacts of biological invasions have also been well studied – these are impacts that affect human health and wellbeing. In our study, we shed light on a third major type of impact caused by biological invasions – animal welfare. Hence, our study provides evidence for the impacts of biological invasions on “One Health” , which is a term used to recognise that the health of the environment, people and animals is interconnected. AWICIS is available online Researchers wishing to report and assess the animal welfare impacts of biological invasions can use the AWICIS Assessment Template . Observations by researchers studying the biodiversity impacts of biological invasions will also be useful to establish the extent and severity of these animal welfare impacts. Hence, they are encouraged to report these observations using the AWICIS Assessment Template. A weekly e-mail in English featuring expertise from scholars and researchers. It provides an introduction to the diversity of research coming out of the continent and considers some of the key issues facing European countries. Get the newsletter! Thomas George Evans a reçu des financements de Animal Welfare Initiative et German Research Foundation (DFG).