Why Does India Have So Many Snakebites? By Rom Whitaker

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This is a complicated subject, most replies to which just generate more questions. But let’s make a stab at it and perhaps it will stimulate some serious research or at least dialogue on the subject.

First we need to establish a few baselines, one of which is the theory of the Big Four medically important snakes of India. There is no argument with the fact that serious and even fatal bites are occasionally reported from other Indian venomous snakes like banded kraits, sea snakes, king cobras and pit vipers. But all the major literature on the subject reports that the cobra (four species), krait (seven species), Russell’s viper and saw-scaled viper (possibly two species) are the Indian snakes that cause the greatest number of serious and fatal bites.

There is too little reliable data to tell us which of the four cause the greatest number of bites or fatalities, but it is abundantly clear that it is highly region-specific. For example in places like Jaisalmer in Rajasthan and Ratnagiri in Maharashtra, over 90% of all venomous bites are from the most common snake there, saw-scaled vipers. This in itself would be a fascinating study, one which herpetologists and medicos could get together on. Determining the prevalence of snake species and their bites have important implications in teaching people how to avoid bites and in instilling confidence in doctors who treat the bites.

High numbers of venomous snakebites, most among rural farmers and labourers seem to indicate several things:

Venomous snakes are present in high densities in agricultural areas – This seems to be true though no one has even done even a basic snake population or breeding biology study in India (or compared field populations of snakes to forest numbers). Certainly the Irula snake hunters who provided millions of cobra, rat snake and Russell’s viper skins to the skin trade concentrated their hunting in agricultural areas, not in forests.

 Factors like the habit of cobras and kraits which protect their eggs during incubation could account for high hatching rates of these venomous species, who knows? And who knows what the survival rate of these babies is? And what do we know about snake dispersal, home range or growth rates? We are sorely lacking the information needed to understand distribution and populations of important snake species and thereby get a better understanding of snakebites.

Prey species occur in high densities in agricultural areas – There is no doubt that this is true, rodents are so incredibly abundant in Indian rice paddies and other agriculture that huge crop losses are commonly reported. Luckily there is plenty of data on rodent population densities and breeding biology from the many studies done by rodent researchers in India. Wouldn’t it be fantastic if some keen young (or old) herpetologist was to take that rodent data and marry it to a snake study. The very strong association of the spectacled cobra with the lesser bandicoot (Bandicota bengalensis) in South Indian rice fields is a potent topic for a PhD or post-doc study. Taking off from George Schaller’s classic ‘The Deer and the Tiger’, how about ‘The Mole Rat and the Cobra’? Any takers?

The prey issue is complex and fascinating: let’s accept as axiomatic that our huge numbers of rodents (we humans tend to encourage wherever we live or farm), create unusually high densities of snakes. We know that cobras are common in rice fields (since we provide rice, water and bunds for lesser bandicoots to tunnel and live in, cobras naturally move in) and that they do cause quite a high percentage of bites in some areas. So is rice the common denominator? Maybe one would have to travel across the rice belt of Asia, all the way to the Philippines to try to figure this one out.

Rice (and other grain crops) certainly seems to be a major reason for high rodent and therefore snake densities. A few quick transect studies in adjacent forests would probably demonstrate just how scarce rodents are there, in comparison to our fields. In a day’s walk with a few Irula snake hunters it’s not unusual to see a dozen rat snakes amongst the paddy; this is a large, conspicuous, harmless diurnal snake and much more likely to be encountered  than any of the Big Four.

And what about the other ‘medically important’ snakes? Well the common krait is also a rodent eater (besides the snakes and skinks it regularly feeds on), but specializes (so the Irulas tell us) in field mice (Mus booduga), just the right size for a thin snake like the krait. And sure enough, kraits like to live in field mice burrows, a nice tight fit. Kraits are not so fond of the paddy field bunds where the cobras live, they prefer larger embankments and especially the old piles of well tailings that dot our countryside. These piles of rocks, soil and debris are quickly colonized by bushes and trees and are ideal habitats for mice and snakes.

Russell’s vipers like cactus, agave, pandanus and other thick, thorny, nasty cover. They are not regular burrow dwellers, though they will get into old termite mounds and larger rodent tunnels at the hottest time of year (I found one in a fox burrow). Interestingly, these rodent and bird eaters apparently have a special favourite (according to the Irulas and a small snake scat study we did some years ago), the Indian gerbil (Tatera indica). I think they are tasty too. Gerbils live in association with rice fields and other crops, usually not in the bunds but they make their distinctive entrance/exit burrows on higher ground bordering the fields such as the banks of earthern dams. Three of the Big Four thus appear to have strong associations with three different rodents and thus, rice and other crop fields.

The saw-scaled viper is the odd one out, not seeming to benefit from agriculture except perhaps for the spinoff of field mice that probably also eat a lot of rice. ‘Sawskies’ as we affectionately call them, like open country and the amount of conversion of good forest land to wasteland that humans do has obviously opened up plenty more habitat for these little fellows. They feed on field mice, lizards, scorpions and probably a host of other arthropods like crickets, roaches, centipedes and spiders. So sawskies aren’t one of our ‘rice field snakes’ though we can blame ourselves for making them at home in our new wastelands.

 Rural people rarely use footwear (most bites are on feet and legs) – This is certainly true, shoes are expensive and impractical for wading around in the mud of a paddy field. Chappals could be called ‘footwear’ but obviously don’t offer much protection from snakebite. Farmers typically go out to fields early in the morning and come back in the evening, just the time when snakes might be out foraging around. Rural people often don’t have toilets and use the bushes, both day and night. No wonder there are so many human/snake encounters.

Rural people rarely use lights at night while walking (most bites are at night) – Batteries are expensive for people like subsistence farmers and labourers, so even if they have a torch they are not likely to have the batteries for it or will just use it sparingly. Inexpensive rechargeable torches are now available, so things are looking up. Statistics about when most snakebites occur are probably fairly reliable and the common wisdom is that 75% or more of the bites happen at night. This is of course species specific and will vary from place to place and even seasonally. All of the Big Four are at least partly nocturnal (the krait strictly so), and especially around human habitation snakes seem to adapt to the security of darkness, putting humans at particular risk. In a series of interviews we made with snakebite patients in Kerala (in an area where Russell’s vipers cause almost all the serious bites) virtually all were bitten at night when they were walking near their homes or on a main path or road, without a light.

The long and the short of it is, we create ideal snake habitats, provide them with abundant prey and produce millions more baby humans each year who will grow up to tromp around these snake habitats with no shoes, knowledge of avoidance and no lights at night. No wonder we have so many snakebites!

In 2011 a study was published called the Million Death Study. Based on interviews by medical personnel and social workers in over a million households in randomly selected locations around India the study ascertained causes of death. The Ministry of Health, Government of India reports less than 1500 deaths by snakebite per year in India. The Million Deaths Study reported 46,000 deaths by snakebite in India per year! (Check out ). PLoS Negl Trop Dis 2011; 5: e1018

Romulus Whitaker

Romulus Whitaker

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