Tag Archives: serpent island

Endangered, Bird-eating Centipedes of Mauritius

Can a centipede really be endangered? Of course!

Centipedes don’t get much love, even from each other. They are solitary, irritable, fiercely cannibalistic, and arguably some of the most widely hated animals on earth. I know many biologists who would gladly handle a snake or tarantula, but shudder at the thought of a giant centipede creeping up their arm.

An Indopacific centipede, making good use of a hole in the wall. Photo by Thomas Brown, licensed under CC BY 2.0.

An Indopacific centipede, making good use of a hole in the wall. Photo by Thomas Brown, licensed under CC BY 2.0.

I never begrudge people for being scared of centipedes. They are objectively frightening: many-legged, venomous, fast-moving, and secretive. In the rural tropics, a painful bite from a giant centipede is a very real possibility. But none of this means they can’t be endangered, put at risk of extinction either by natural circumstance or by human activity.

Unsurprisingly, very few centipedes have ever been studied from a conservation-oriented perspective. Most of the time, there simply isn’t the funding, public interest, or lack of squeamishness to make that kind of research happen. There are, however, exceptions. Today I’m going to tell you about one: the giant centipedes of Mauritius and Rodrigues.

Mauritius, Rodrigues, and their satellites form a collection of tiny islands in the Indian Ocean, just a few thousand miles east of Madagascar. Like most islands they have a long, sad history of extinctions wrought by over-hunting, invasive species, and habitat destruction. The dodo bird, native to Mauritius, was one of the first victims.

Mauritius.png

Mauritius, in panoramic view. Photo by Clément Larher, licensed under CC BY-SA 3.0.

The two main islands are home to two species of giant centipede, the blue-legged (Scolopendra morsitans) and the Indopacfic (Scolopendra subspinipes) centipedes*. Both species are incredibly efficient predators, and with body lengths of 8 inches or more, they are more than capable of tackling large prey such as mice. On Mauritius, staple fare include house geckos and cockroaches, but they also take day-old chicks from their nests when opportunity strikes (Lewis et al. 2010). The Indopacific centipede can even swim, undulating side-to-side while holding its head above the surface like a crocodile (Lewis 1980).

Despite their size, venom, and general badassness, giant centipedes are prey for many larger animals. On Mauritius, they form 80% of the diet of feral cats that roam the island by night. The cats are apparently nimble (and daring) enough to tear apart the centipedes without getting bitten.

An Indopacific centipede from China. Photo by Thomas Brown, licensed under CC BY 2.0.

An Indopacific centipede from China. Photo by Thomas Brown, licensed under CC BY 2.0.

Even in the face of predation by cats, giant centipedes remained abundant until 1997, when a new invasive species came into the picture. That species was the musk shrew (Suncus murinus), introduced from India. A smaller shrew might become prey for a centipede, but the musk shrew is the largest in the world, reaching a length of 6 inches or more.

An 8-inch-long centipede is still a formidable adversary, but the shrews were used to encountering giant centipedes in their native range (as it happens, the Indopacific centipede also lives in India). They have made short work of centipede populations, which are now greatly reduced (Lewis et al. 2010). The Indopacific centipede is now found on Rodrigues, but no longer on Mauritius, while the blue-legged centipede is still found on both islands.

Mauritius and its satellite islands. From Lewis et al. (2010), licensed under CC BY 4.0.

Mauritius and its satellite islands. From Lewis et al. (2010), licensed under CC BY 4.0.

I am not about to launch into a passionate defense of blue-legged and Indopacific centipedes. As I said before, both species are abundant in tropical habitats all over the world, from Indonesia to the Caribbean. For all we know the centipedes themselves are invasive, dancing with cats and shrews on the graves of long-gone native species. Instead this article is about another giant, a third centipede, gone from Mauritius but still clinging to life on Serpent Island.

Serpent Island is a satellite of Mauritius, uninhabited by humans and with an area less than 100 acres. There is very little vegetation or soil there, and bare rock dominates the surface. In the absence of humans or large predators, sea birds thrive, especially sooty terns which nest by the thousands on open ground.

They share the space with centipedes — not Indopacific or blue-legged, but Serpent Island giant centipedes (Scolopendra abnormis), which are found on one other satellite island (Round Island) and nowhere else on earth — not even Mauritius. The centipedes are abundant on Serpent Island, with roughly 12 individuals per square meter. If centipedes frighten you, don’t plan your next vacation here.

During the day centipedes hide beneath rocky slabs and underground, away from the light and from watchful, easily enraged mother birds. Terns are active during the day, flying from land to sea and back again, gathering fish for their hungry chicks. With all the traffic, a centipede is better off staying out of sight.

A sooty tern. Photo by Duncan Wright, in public domain.

A sooty tern. Photo by Duncan Wright, in public domain.

By night the terns are less wary. Snakes, which would normally prey on tern chicks, are absent from the island, probably driven out soon after the arrival of European explorers. Without the competition, centipedes have risen to take their place. Wandering over the rocks, a centipede uses smell and touch to locate a nest, grab hold of a chick, and sink in its venom-laden fangs. More than any so-called bird-eating tarantula, the Serpent Island centipede is a true bird-eater. In captivity, they can survive for several years on a diet of chick legs (Lewis et al. 2010).

The taste for bird meat is probably a recent acquisition — Serpent Island centipedes most likely colonized the island only a few million years ago. They would have arrived from Mauritius, suggesting the larger island had a population of Serpent Island centipedes before they were driven to extinction by the introduced shrews, cats, and perhaps larger centipedes.

The Serpent Island centipede is classified as Vulnerable by the International Union for Conservation of Nature (IUCN 2012). This means the species is  “considered to be facing a high risk of extinction in the wild.” It is one of 10 potentially threatened centipedes on the IUCN Red List (of 3,300 total centipede species worldwide). So far, none have been given legal protection.

Centipede snacks. Photo by Duncan Wright, in public domain.

Centipede food. Photo by Duncan Wright, in public domain.

The bad news is that, if shrews or cats or rats were to be introduced to Serpent Island, the entire ecosystem would collapse. Invasive predators would quickly eat both chicks and centipedes, leaving Serpent Island a bare rock in the middle of the ocean, with a few tufts of grass and the occasional cockroach.

The good news is that centipedes are abundant in their last remaining habitats, with an estimated population of 10-15,000. Serpent Island is remote and protected, and biologists are pretty much the only visitors, so it is unlikely shrews will ever get there. The future of Serpent Island’s bird-eating centipedes is secure, for now.

Reminder: there are still 6 days left to donate to Dr. Adam Britton’s crowdfunding campaign to study threatened pygmy crocodiles in Australia! I’ve donated, and I encourage you to so if you think pygmy crocodiles, which you can read about here, are awesome, which of course they are. There are some amazing prizes for donors, including crocodile-themed artwork and jewelry!

*These species normally go by the common names Tanzanian giant (blue-legged) and Vietnamese giant (Indopacific). However, both are extremely wide-ranging in tropical habitats all over the world, including Hawaii where they have been introduced by humans (Shelley et al. 2014). To reduce confusion I used alternative common names.

Cited:

IUCN. 2012. IUCN Red List Categories and Criteria: Version 3.1. Second edition. Gland, Switzerland and Cambridge, UK: IUCN. iv + 32pp.

Lewis J.G.E., P. Daszak, C.G. Jones, J.D. Cottingham, E.Wenman, and A. Maljkovic. 2010. Field observations on three scolopendrid centipedes from Mauritius and Rodrigues (Indian Ocean) (Chilopoda: Scolopendromorpha). International Journal of Myriapodology 3: 123-137.

Lewis J.G.E. 1980. Swimming in the centipede Scolopendra subspinipes Leach (Chilopoda, Scolopendromorpha). Entomologists Monthly Magazine 116: 219-220.

Shelley R.M., W.D. Perreira, and D.A. Yee. 2014. The centipede Scolopendra morsitans L., 1758, new to the Hawaiian fauna, and potential representatives of the “S. subspinipes Leach, 1815, complex” (Scolopendromorpha: Scolopendridae: Scolopendrinae). Insecta Mundi 338: 1-4.

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