The giant bird-eating centipedes may look like something out of a sci-fi movie, but they’re not.
On little Phillip Island, which is part of the South Pacific Norfolk Island Group, the Phillip Island centipede (Cormocephalus coynei) the population can kill and eat up to 3,700 seabird chicks each year.
And this is quite natural. This unique creature endemic to Phillip Island has a diet consisting of an unusually high proportion of vertebrate animals including seabird chicks.
Phillip Island in the Norfolk Island Group, with a valley of iconic Norfolk Island pines. (Luc Halpin)
We show how predators arthropods can play an important role in the food webs of island ecosystems. And the Phillip Island centipede achieves this thanks to its very varied diet.
A well-armed predator flutters in the night
This centipede can grow up to almost a foot (or 30.5 cm) long. He is armed with a powerful venom enclosed in two pincer-shaped appendages called “forcipules”, which it uses to immobilize its prey. Its body is protected by armored shield-shaped plates that line each of the many segments that make up its length.
Phillip Island millipede and black-winged petrel. (Luke Halpin, author provided)
On hot and humid nights, these nocturnal arthropods hunt in a thick leaf litter, navigating a maze of seabird burrows dotted across the forest floor. A prey centipede will use its two ultra-sensitive antennae to navigate in search of prey.
The centipede hunts a surprisingly diverse range of careers, from crickets and seabird chicks to geckos and skinks. It even hunts fish – abandoned by seabirds called black noddies ( Anous minuta) that make their nests in the trees above.
A frightening discovery
Shortly after starting our research on the ecology of Phillip Island’s burrowing seabirds, we discovered chicks from black winged petrels (Pterodroma nigripennis) were the prey of the Phillip Island centipede.
We knew this needed further investigation, so we set out to unravel the mystery of the eating habits of this large arthropod.
Black-winged Petrel chick just before being weighed on Phillip Island. (Trudy Chatwin)
To find out what these centipedes ate, we studied their feeding activities at night and recorded the prey species they were targeting. We also monitored the petrel chicks in their burrow nests every few days, for months at a time.
We eventually started to see consistent injury patterns in the chicks that were killed. We even saw a centipede attacking and eating a chick.
From the predation rates we observed, we calculated that the Phillip Island centipede population can kill and eat between 2,109 and 3,724 petrel chicks each year. Black-winged petrels – of which there are up to 19,000 breeding pairs on the island – appear to resist this level of predation.
And predation of black-winged petrels by Phillip Island centipedes is an entirely natural predator-prey relationship. By preying on vertebrates, centipedes trap nutrients brought in by seabirds from the ocean and distribute them around the island.
In a sense, they took the place (or ecological niche) predatory mammals, absent from the island.
Luke Halpin tending to black winged petrel chicks on Phillip Island. (Trudy Chatwin)
Restoration and recovery
Until just a few decades ago, the Phillip Island centipede was very rare. In fact, it was only formally described as a species in 1984.
After an intensive search in 1980, only a few small individuals were found. The rarity of the species at the time was probably due to the severely degraded habitats caused by pigs, goats and rabbits introduced by humans to the island.
The elimination of these invasive pests allowed the colonization of black-winged petrels. Their population has since exploded and they are now the most abundant of the 13 species of seabirds that breed on Phillip Island.
They provide a high quality food source for the Phillip Island centipede and therefore have likely helped the centipede population to recover.
Ancient bone deposits in the ground suggest that before the arrival of the Black-winged Petrel, Phillip Island was home to a large number of other small species of burrow-nesting seabirds. It is likely that the Phillip Island centipede also preyed on these seabirds.
Now, thanks to the conservation efforts of Norfolk Island National Park, the island’s forest is regenerating alongside endemic species like the centipede, as well as the critically endangered Phillip Island hibiscus (Hibiscus insularis).
As a driver of nutrient transfer, the persistence of the Phillip Island centipede (and its healthy appetite) may well be the key to restoring the island’s ecosystem. But we will need to do more research to fully understand the complex links in this bustling food web.