Snakes of Madagascar: Cultural and Ecological Roles
Madagascar’s snakes have been the subject of almost 300 years of research. Most of this work has been taxonomic – with ~98 described species, and at least five undescribed species remaining, we are only now approaching the end of the taxonomic era for the island’s snakes (but are nowhere near for frogs and some lizard groups). Because we have been emphasising the naming of species, we have not yet devoted much time to figuring out the roles of the species in their ecosystems. This, then, is likely to be the future of snake research in Madagascar. As this research slowly picks up, and the available knowledge increases, a clearer picture of ecological patterns among species is emerging, and over the coming years, this picture is set to dramatically improve.
In this article, I will give a brief overview of current knowledge of Madagascar’s snakes, their roles in ecosystem services, and some interesting characters that have emerged. I will touch on not only the role of snakes in their own ecosystems, but also the role of local culture and taboos in shaping the future of Madagascar’s snakes, and their influence of the snakes’ ability to fulfill their roles in the island’s complex and poorly understood food webs.
A Brief Overview of Madagascar’s Snakes
Madagascar has four snake radiations: pseudoxyrhophiine snakes (~79 species in 18 genera), a single psammophiine snake (Mimophis mahfalensis) (Note: Pseudoxyrhophiinae and Psammophiinae used to be called ‘colubrids’, but were recently moved to the Elapoidea because of their genetic affinities – Wikipedia is VERY outdated on this issue, so don’t bother trying to look it up), boas (three species in two genera), and blindsnakes (two families: Typhlopidae – about 14 known species in two genera; and Xenotyphlopidae – one genus with two species).
The four separate snake lineages mean that snakes arrived on Madagascar at least four separate times. Only one lineage, the Xenotyphlopidae, is older than Madagascar as an island, and so was almost undoubtedly on the island before it became an island. The first colonisers to arrive may have been other blind snakes – typhlopids, some 65 million years ago (it’s possible that they, like Xenotyphlopidae, speciated in situ – that is to say, that they were in Madagascar after it broke off of the west coast of Africa, and before India went skittering across the Indian ocean and slammed into mainland Asia) (Vidal et al., 2010). About 35 million years later, around the same time as one another, pseduoxyrhophiine snakes and boas arrived on the island (Nagy et al., 2003; Noonan & Chippindale, 2006a). Then, 10 million years ago, a psammophiine snake arrived, and this lineage is represented today by just the one species, Mimophis mahfalensis. To add symmetry, it seems like the most recent coloniser of Madagascar was again a typhlopid - Ramphotyphlops braminus, commonly known as the flower-pot snake, is today present throughout the tropics, and probably arrived on the island within the last 2000 years.
The colonisation of Madagascar was followed by a somewhat explosive diversification, as is common on islands. This diversification included the evolution of several different diets and eating habits, especially among the pseudoxyrhophiine snakes. As it happens, a friend and colleague of mine, Cynthia Wang, is working on the evolution of dentition in this group – this research will hopefully give us a much clearer idea of the evolutionary history of these snakes, and the potential ecological drivers for speciation.
Dietary Specialisations and Generality:
To illustrate the role snakes have in Madagascar’s food webs, allow me first to cover some interesting patterns of dietary specialisation that have emerged. These comments are patchy at best – our knowledge really doesn’t allow for broad statements about group ecology, but is entirely species-specific at this stage.
Madagascar is probably best known for its mammal diversity – the charismatic lemurs get the majority of international attention. But in comparison to the island’s reptile and amphibian diversity, the mammals begin to look depauperate. An estimated 530 species of frogs are present, 99% of which are found nowhere else on the planet (i.e. endemic), and upwards of 400 reptile species are present as well, 82% of which are also endemic. And, as I’ve already said, about 98 of these are snakes. Given this relatively high herpetofaunal diversity, it should come as no surprise that many of Madagascar’s snakes are known to have reptiles and amphibians in their diets. Cases of snakes eating lizards, particularly chameleons and geckos, have been frequently reported (and conveniently also photographed), and apparently most of Madagascar’s snakes are, to coin a new term, ‘herpivores’ – their diets contain nothing but reptiles and amphibians (Mercurio et al., 2006; Glaw & Vences, 2007).
Mimophis mahfalensis eating a Chalarodon madagascariensis, an iguanid lizard. Photo by Louise D. Jasper [X]
Although many species are generalist feeders (see below), one group of snakes has earned a reputation for being extremely stingy. The cryptic leaf-nosed snakes, Langaha spp., are specialised lizard-eaters. They wait, unseen, until a prey item strays too near, and then strike. Until recently, they were thought to feed exclusively on tree-dwelling lizards, but Jessica Tingle revealed that they do in fact feed on some terrestrial species as well (Tingle, 2012).
Langaha madagascariensis male, consuming yet another unfortunate Chalarodon madagascariensis. From Tingle (2012).
Despite this reputation for a limited diet, Langaha seems to eat more than just lizards, and has been known to eat frogs in the wild. But there is little doubt that it is an exclusive herpivore.
A very limited diet appears also to be present in some other species, such as Compsophis laphystius, which is only known to eat frogs and their eggs. Similarly, it is possible that Micropisthodon ochraceus may be an exclusive snail-eater. Thus, it is clear that some of Madagascar’s snakes have very specific and inflexible roles in their local food chains.
Ophiophagy – the eating of snakes – has been reported from very few snake species, including Liophidium vaillanti, by Vincenzo Mercurio and his colleagues (2006), and also Madagascarophis species (see below) and Mimophis mahfalensis (Glaw & Vences, 2007). This is an interesting example of inter-predator predation, and might have a regulatory role in these food webs. However, no exclusive ophiophages are known from the island, and it is unclear how often it happens in the wild.
The consumption of invertebrates is a fairly rare trait among snakes as well. Madagascar has several very small snake species (Pararhadinea melanogaster, for example, has a maximum total length of just 240 mm), which are likely to have predominantly invertebrate diets. As mentioned above, Micropisthodon ochraceus appears to eat snails, although the rest of its diet is unknown.
Oophagy – egg-eating – has a high ecological impact for prey species. Leioheterodon madagascariensis, Madagascar’s giant hognose snake, and other members of the genus Leioheterodon, are known to be egg-eaters – they actively seek out the recently-laid eggs of lizards (and also other snakes), and consume them.
Leioheterodon madagascariensis feeding on the freshly laid eggs of this Oplurus cuvieri, a different species of iguana – they’re having a rough time, these iguanas! Photo by Bill Love [X]
Leioheterodon are certainly not egg-specialist feeders, although they do appear to have a preference for eggs over any food. Nonetheless, this behaviour is very interesting, because it means snake predation on lizards affects them throughout their life cycle, including during development. Leioheterodon madagascariensis appears also to have another role in the island’s ecosystems, which is to be crocodile lunch.
This is likely to be a fluke of a photograph however – I cannot imagine these snakes make up a large part of the crocodiles’ diets.
Madagascar’s boas are the island’s second largest predators, surpassed only by crocodiles. They will eat anything from lemurs to birds, to lizards and large frogs, and everything in between.
It is really not a great day to be an iguana. Here Acrantophis madagascariensis eating an Oplurus lizard.
This makes them key ecological players, at the top of the island-wide foodweb. Furthermore, adults have no surviving natural predators (they have been predated upon by extinct giant eagles historically, and are rarely preyed upon by crocodiles today), and so these snake populations are fairly stable, but very susceptible to human activity (and especially to introduced species, such as dogs, which might pose a threat even to large individuals).
Of all of Madagascar’s snakes, Madagascarophis spp., the cat-eyed snakes, stand out the most in terms of diet generality. I have personally observed these snakes eating chameleons, geckos, frogs, and small mammals, and they have also been reported to eat fish, birds, and any eggs they come across.
Madagascarophis colubrinus devouring a mouse. Photo by Mark Scherz [X]
This dietary generality may mean that these snakes are extremely important predators across Madagascar, regulating everything from mouse (including within large towns and ‘cities’) to lizard numbers. These snakes are especially common in inhabited areas, because of the resulting increase in rodents.
Snakes are Madagascar’s most important large predators. While the fossa (Cryptoprocta ferox) and some birds of prey also contribute significantly to the top-down regulation of the island’s ecosystems, snakes are the most diverse, abundant, and widespread predators. The consumption of rats (of both the black and brown varieties) by larger species is extremely important, as these invasive species have the potential to overrun Madagascar’s endemic small-mammal diversity, and are also responsible for the persistence of the bubonic plague in western Madagascar. Mice are another such accidental introduction into the island, but they form a large part of the diet of Madagascarophis spp., and so these may also be kept in check by snakes.
It is possible that the increase in available prey as a result of introduced rodents may have led to explosions in rodent-eating snake numbers as well. This in turn may have had knock-on effects for other prey items, which would likely suffer from the increased predation by the additional snakes. Although this system may reach an equilibrium (and may have already), it is likely that several species in the food web will have been very badly impacted by these dynamics. Research will be needed to look for any dynamics of this kind.
Human-Snake Interactions: Conflict and Taboo
Because of their predilection for animals that are typically most abundant around humans (i.e. rats and mice), boas and cat-eyed snakes have developed a commensal relationship with human habitations. Thus, the people of Madagascar most frequently come into contact with these species, while most other species are rarely seen outside of forests.
Most Malagasy people I have encountered are terrified of snakes, and would rather not have them living in their houses, and I have frequently been called to rescue a frightened home-owner from a harmless snake which was discovered in their house. Conflict between the people and their unwelcome lodgers results in a lot of snake deaths, because they view the snakes as a threat, and are afraid of them.
The ingrained fear towards snakes has given rise to some very interesting taboos (much of Madagascar’s rural population have a highly taboo-driven culture). One notable taboo I have encountered in southern Madagascar is the tale of the ‘spear’ snake. This snake, when it meets you, is said to straighten itself out like a spear, and will fly straight through your chest. It is unclear whether this story concerns Leioheterodon, which have somewhat pointed snouts, or Langaha, with their long spear-like nasal projection.
Not all of the taboos are bad for the snakes. In northern Madagascar, there is a group of people who think that boas are their reincarnated ancestors. Should they find a boa crossing their path, they will spend some time trying to figure out which of their ancestors it most resembles, and would certainly not kill the animal, for it is held in reverence. This type of taboo yields an in-built conservation mechanism for these species, so while it does not apply to the majority of snakes, it is very good for the few it does affect.
One of our guards in southern Madagascar posing with a ground boa, Acrantophis dumerili. Photo by Mark Scherz [X]
Conclusions and Future Perspectives
While we are not certain exactly how all of the pieces of Madagascar’s food web puzzle fit together, one thing is clear: snakes have a variety of very important roles, and we know almost nothing about them. Some are highly specialised predators, possibly involved in only specific food chains, while others are extremely general in their eating habits, and act as top-down regulators for whole ecosystems. While some are abundant – Mimophis mahfalensis is colloquially referred to (by my team, at least) as the ‘common-as-dirt snake’ – others, such as Thamnosophis mavotenda, are known only from very few individuals or even single specimens.
And if we know little about the predatory habits of the snakes themselves, we know practically nothing of the species that predate them! While Madagascar Harriers are known to consume some snakes, it is not known which species they hunt (Rene de Roland et al., 2004). The subject of ecological roles of snakes in Madagascar is set to become a very important topic of research in the coming years.
Madagascar’s snakes, like all of the island’s herpetofauna, are highly threatened. Not only is there a huge threat from deforestation (which I won’t talk about here because I could write a whole article about it), but there are also direct anthropogenic pressures on snakes. Many are killed when encountered by Malagasy people, as only few are spared by beneficial taboos, but there is also on-going collection for the leather and illegal pet trades, as well as a disturbingly high incidence of snake road kill, all of which are probably resulting in drastic declines in snake numbers. As Madagascar’s forests disappear and snakes come into ever more frequent contact with humans, they will continue to decline, at an ever-increasing rate. Thus, there is an increasing sense that we are working against the clock, to understand the species, before they disappear altogether.
This piece has been produced as part of a blogging carnival. Other authors have published other pieces on the common theme ‘Snake Ecosystem Services’; check them out!:
Snakes and the Ecology of Fear by Bree Putman
Ecology of Snake Sheds by Andrew Durso
Good Neighbors Make a Greater Impact by Melissa Amarello
When the Frogs Go, the Snakes Follow by Jodi Rowley
Kingsnakes Keep Copperheads in Check by David Steen
Converting Converting Ophidiophobes to Ophidiophiles, One Kid at a Time by Emily Taylor
Pythons as Model Organisms by Heidi Smith Parke
The Brown Treesnake of Guam by Brian Barczyk
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Glaw, F. & Vences, M., 2007. A Field Guide to the Reptiles and Amphibians of Madagascar. 3rd ed. Cologne, Germany: Vences & Glaw Verlags GbR.
Mercurio, V., Mattioli, F., Razafindrabe, T.J. & Andreone, F., 2006. A possible attempt of predation of Liophidium vaillanti upon Dromicodryas bernieri observed in central-southern Madagascar (Serpentes: Colubridae). Salamandra, 42(2), pp.181-83.
Nagy, Z.T. et al., 2003. Multiple colonization of Madagascar and Socotra by colubrid snakes: evidence from nuclear and mitochondrial gene phylogenies. Proc. R. Soc. Lond. B, 270, pp.2613-21.
Noonan, B.P. & Chippindale, P.T., 2006a. Dispersal and vicariance: The complex evolutionary history of boid snakes. Molecular Phylogenetics and Evolution, 40, pp.347-58.
Rene de Roland, L.-A., Rabearivony, J. & Randriamanga, I., 2004. Nesting biology and diet of the Madagascar harrier (Circus macrosceles) in Ambohitantely Special Reserve, Madagascar. Journal of Raptor Research, 38(3), pp.256-62.
Tingle, J.L., 2012. Field observations on the behavioural ecology of the Madagascan leaf-nosed snake, Langaha madagascariensis. Herpetological Conservation and Biology, 7(3), pp.442-48.
Vidal, N. et al., 2010. Blindsnake evolutionary tree reveals long history on Gondwana. Biology Letters, 6(4), pp.558-61.