Summer is the time of the year when many people find strange bugs in the house. Most are harmless and many are beneficial when outdoors, so it’s a nice gesture to catch-and-release rather than smash-and-flush. Those options are not available to the residents of Philip Island in the South Pacific, where one species of centipede is not only giant – it’s the apex predator of the island. How apex? A new study found these footlong creatures are the consumers of thousands of baby seabirds every year – seabirds who were once themselves the apex predators of Philip Island. How did this happen? Think ‘invasive species’ and you have the answer.
“From the rates of predation we observed, we calculated that the Phillip Island centipede population can kill and eat between 2,109 and 3,724 petrel chicks each year. The black-winged petrels — of which there are up to 19,000 breeding pairs on the island — appear to be resilient to this level of predation.”
Luke Halpin, ecologist at Monash University, Rohan Clarke, Senior Lecturer in Ecology at Monash, and Rowan Mott, biologist at Monash University, were studying the ecology of Phillip Island’s burrowing seabirds when they noticed that the chicks of black-winged petrels (Pterodroma nigripennis) were falling prey to the Phillip Island centipede. As they explain in their study, published in The American Naturalist, and their summary in The Conversation, Phillip Island is uninhabited and the black-winged petrels were apex birds there until just a few years ago. The Phillip Island Centipede (Cormocephalus coynei) had been extremely rare and was only identified in 1984. It’s rarity was due to pigs, goats and rabbits brought by humans to the island. When those creatures were removed, the habitat recovered and thrived … and so did the black-winged petrels. Unfortunately, so did the giant centipedes – especially when there were suddenly more baby chicks to eat.
“Petrels produce a single offspring per year; therefore, predation of nestlings by centipedes represents total breeding failure for a pair in a given year. Our work demonstrates that arthropods can play a leading role in influencing vertebrate reproductive output and modifying trophic structures and nutrient flow in island ecosystems.”
Despite up to nearly 4,000 of the 19,000 breeding pairs losing their only chick annually, the birds have managed to stay at the top of the scale amongst the island’s other birds. Meanwhile the giant centipedes vary their diets on geckos, skinks, fish and other small arthropods. Together, the black-winged petrels and giant centipedes (photos of both here) maintain a delicate balance on Philips Island. As bad as that sounds, things could be worse.
“It’s totally surprising and rather horrifying. The tortoise is deliberately pursuing this bird and kills it, and then eats it. So yeah, it’s hunting.”
On the Seychelles archipelago off the coast of East Africa, live giant Aldabra tortoises – the only other place to find the “gentle giants” besides the Galapagos. Unfortunately, as Justin Gerlach, an island ecologist and co-author of a study published in Current Biology, told The New York Times, they’re not so gentle when they find baby birds. While it was known that they would eat chicks that fall from nests, a recent video captured for the first time a giant tortoise slowly stalking a tern chick, catching it and gobbling the bird down whole like it does this all the time – which the researchers say in the study that they probably do all of the time.
“We’re used to thinking of them as being not particularly interesting, slow moving and probably quite stupid. But clearly there is so much more to these animals.”
In nature as well as in relationships, ‘cute’ does not always mean nice. Wonder which would win in a cage match between a giant tortoise and a giant centipede?
Those little centipedes in your kitchen don’t seem so scary anymore, do they?