When Birgit Fessl reached into a tree branch on Santa Cruz Island in 1997 to collect a woodpecker finch's nest, she discovered something that would reshape how scientists measure suffering across the world: a dying chick, another sucked dry, and 20 large maggots full of blood. The avian vampire fly (Philornis downsi) had arrived in the Galápagos Islands decades earlier from mainland Ecuador, invisible to researchers until that moment of accidental discovery. What Fessl witnessed wasn't an isolated tragedy. "Then I realized it wasn't an accident: It was everywhere," she recalls. Across every human-inhabited island in the archipelago, these parasitic flies had already killed chicks and maimed others for life, yet the suffering had gone unmeasured and largely unseen.
The vampire fly story illustrates a critical blind spot in how conservation science counts the cost of invasive species. Around the world, more than 37,000 invasive species have been introduced to new environments, wreaking devastation that remains largely invisible through existing measurement systems. Yellow crazy ants in Japan spray acid into the eyes of shrikes. Toxic cane toads in Australia cause quolls to bleed from the nose. Yet none of this suffering appears in the global standard for assessing species invasions, which focuses narrowly on environmental and biodiversity impacts. The framework simply wasn't built to capture animal welfare—until now.
In May, an international team of researchers published AWICIS, the Animal Welfare Impact Classification for Invasion Science, a new system designed to quantify the suffering that invasive species inflict on wildlife. Thomas Evans of the Free University of Berlin and Michael Mendl of the University of Bristol co-designed the framework after testing it across hundreds of documented cases of bird and ant invasions worldwide. The results were striking: the system revealed that smaller invasive species cause suffering at scales that current biodiversity-focused frameworks systematically overlook.
AWICIS works by asking researchers and conservationists to evaluate multiple indirect indicators of suffering—physical, behavioral, and psychological—alongside how that suffering occurs, from parasitism to direct predation to resource competition, and for how long. The final impact score adjusts according to how confident scientists are in their grading. Kevin Smith, head of the International Union for Conservation of Nature's invasive species and wildlife health program, called the framework "a useful and practicable tool" that could transform how the conservation community engages the public and decision-makers on invasive species.
Yet the framework's initial global assessment exposed another gap: a significant lack of research on invasive welfare impacts in lower-income countries. Its authors hope that AWICIS adoption will encourage systematic, regular documentation of suffering worldwide, filling these blind spots and extending moral consideration to animals harmed by human-driven species introductions.
Evans believes this work addresses a fundamental ethical question. "We're the driver of these introductions, so we have a moral responsibility to put them right," he says. For the first time, that responsibility now has a standardized way to be measured and tracked.