Six years after Lord Howe Island finished one of the most ambitious rodent eradication programs ever attempted, the island''s insects, spiders and other invertebrates are roaring back.
A study published in the journal Biological Invasions and led by researchers at the University of Sydney compared invertebrate samples collected before the 2019 eradication, in 2016 and 2017, with new samples gathered in 2023 and 2024. Across 20 forest sites, the team collected more than 24,000 specimens — a snapshot of how a small subtropical ecosystem rebuilds itself once invasive predators are removed.
The headline finding: total invertebrate abundance has risen significantly across the island. The biggest gains showed up among larger-bodied species — the kinds most exposed to rodent predation, because rats and mice find them easy to catch and worth the calories. Native cockroaches, beetles, weevils and other forest-floor invertebrates have all moved closer to what scientists believe the island should look like.
Lord Howe Island sits roughly 600 kilometres off the New South Wales coast. It is a UNESCO World Heritage site, famous for its endemic palms, soaring volcanic peaks and seabird colonies. It is also small — about 14.5 square kilometres — and that geography is what made the eradication feasible in the first place.
Rats arrived after a shipwreck in 1918 and quickly began chewing through the island''s wildlife. Over the next century, they were blamed for the extinction of multiple native bird and invertebrate species, including the famous Lord Howe Island stick insect, which survived only on a nearby rocky outcrop. House mice piled on later, hammering ground-dwelling insects in particular.
The rodent eradication program, completed in 2019 by the Lord Howe Island Board with state and federal support, involved aerial and bait-station distribution across the entire island, paired with a long monitoring phase to confirm no rodents remained. It was expensive, controversial in places, and required years of community consultation. By 2021, the island was officially declared rodent-free.
The new study is the clearest evidence yet that the bet is paying off. Beyond raw numbers, the team found shifts in community composition — the mix of species — moving toward what would be expected on a healthy oceanic island. Some smaller invertebrates, which had been thriving partly because their larger predators were being eaten by rodents, became less dominant as the bigger species recovered.
Lead authors describe the rebound as a textbook case of "trophic cascade in reverse." Remove a top consumer that should not have been there, and the ecosystem starts repairing itself from the bottom up. Insects matter because almost everything else above them on the food web — birds, lizards, fish in nearby streams — eats them or relies on them to pollinate, decompose and recycle nutrients.
For conservation managers, the result is also a strong proof of concept for similar projects elsewhere. Island eradications around the world, from New Zealand''s offshore islands to the sub-Antarctic, have rescued seabird colonies, plants and reptiles. Until recently, invertebrate responses were rarely measured with this level of detail. The Lord Howe data set is one of the most comprehensive yet assembled.
The researchers caution that the work is not done. A few smaller invertebrate groups have not yet rebounded, and some endemic species may need active reintroductions to recover fully. Long-term monitoring will continue across the island''s forests, beaches and high-elevation cloud forest.
But the overall picture is one of a small island quietly returning to itself. Walking through the Kentia palm forest at dusk, naturalists report hearing and seeing more activity than they have in years — a faint, very welcome reminder of what the place was like before its accidental tenants arrived.
