When invasive rats and mice vanished from Lord Howe Island in 2019, something unexpected began to bloom in the forest floor. Beetles the size of thumbs emerged. Cockroaches returned. Woodlice that had been hunted nearly to silence for over a century found refuge in leaf litter and logs. Now, researchers from the University of Sydney have documented what those returned creatures mean: an ecosystem fundamentally reorganizing itself after a century of predation pressure lifted.
The island-wide eradication of black rats and house mice—the world's largest rodent removal on an inhabited island—triggered a cascade of ecological recovery that extends far beyond the charismatic birds and reptiles that first showed signs of rebound. A comprehensive study led by Ph.D. candidate Maxim Adams and the NSW Department of Climate Change, Energy, the Environment and Water reveals that invertebrates, the foundation of all island ecosystems, are surging back with dramatic force.
The researchers collected more than 24,000 invertebrate specimens from 20 forest sites across the island, comparing samples taken before the 2019 eradication with fresh collections in 2023–24. What they found was unmistakable: total invertebrate abundance increased significantly, particularly among larger-bodied species that had been most vulnerable to rodent predation. Bush cockroaches and woodlice showed especially strong increases, reshaping the composition of the island's invertebrate communities entirely.
The strongest bounces came among invertebrates larger than 13 millimeters—creatures that had been systematically hunted by rodents for generations. "That matters because these animals are also an important food source for native predators, including geckos and insect-eating birds," Adams explained. The recovery suggests an ecosystem beginning to knit itself back together, with invertebrate populations already fueling documented rebounds in species like the Lord Howe woodhen, a flightless bird that depends on healthy invertebrate communities for survival.
Yet the story is not one of simple restoration to some pristine state. Professor Nathan Lo, who leads the Molecular Ecology, Evolution and Phylogenomics laboratory, cautions that "recovery after invasive species removal can take years or decades, and ecosystems may settle into entirely new configurations." While total invertebrate abundance surged, diversity patterns remained mixed, with some groups flourishing while others declined. Seasonal variation also persisted, and the study could not entirely exclude other environmental factors like climate shifts or habitat changes.
The research focused on ground and lower-tree-dwelling invertebrates rather than canopy or aquatic species, leaving room for future investigation. Adams emphasizes that "invertebrates make up most of the biodiversity in many ecosystems, but they're often omitted because they're difficult and time-consuming to study." His team's findings underscore why that must change: invertebrates pollinate plants, recycle nutrients, break down organic matter, and anchor the food webs that sustain everything else. Without them, broader ecosystem recovery stalls.
The team now plans genetic analyses to identify which species are increasing and whether ecological changes differ between feeding groups or habitats. They also hope to trace longer-term impacts on soil nutrients and decomposition processes—the invisible machinery that invertebrates drive. On Lord Howe Island, a transformed ecosystem is demonstrating that when humans remove the invasive species they once introduced, nature does not simply rewind to the past. Instead, it reorganizes, rebuilds, and reaches toward something new.