ENEMIES, DEFENSE, HUMAN THREATS AND CONSERVATION STRATEGIES

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Snakes have many natural enemies. Small snakes may fall foul of large venomous invertebrates, but it is among other vertebrates that most snake predators are to be found. To avoid being killed and eaten, snakes have evolved an entire armory of weapons and subterfuges.

ENEMIES

Probably the most well known of all “snake killers” is the mongoose, famously embodied as Rikki-Tikki-Tavi in Rudyard Kipling’s Jungle Book. But these agile mammals are not confined to India; there are also mongooses throughout Southeast Asia and Africa. With their quick reactions and thick body fur, and a degree of immunity to cobra venom, mongooses are able to avoid, ward off, and even survive most snake strikes. Seen as a means of controlling snakes and rats, mongooses were introduced to Okinawa, Jamaica, Hawaii, Fiji, Mauritius, and other islands, where they have caused considerable environmental damage and extinctions. Less well known than the mongoose story is the fact that the European hedgehog will also kill and eat snakes, as will many smaller carnivores such as cats.

Among the birds, snake-eagles, fish-eagles, hornbills, and secretary birds are all snake predators. In the reptiles, crocodiles, monitor lizards, and ophiophagous snakes—especially the King Cobra (Ophiophagus hannah), American kingsnakes (Lampropeltis), and African filesnakes (Gonionotophis) —all prey on snakes. After all, nothing fits inside a snake so well as another snake! Even the most venomous snakes, the seasnakes, are commonly found in the stomachs of tiger sharks. But humankind is the snake’s worst enemy.

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The large East African Gaboon Viper (Bitis gabonica) has a body patterned like a pastel-colored Persian carpet, and a head like a huge leaf. This complex cryptic patterning serves to break up its outline when it is lying in woodland leaf litter.

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The venomous Eastern Coralsnake (Micrurus fulvius, top) can be distinguished from its harmless mimic, the Scarlet Milksnake (Lampropeltis elapsoides, bottom) by the order of its bands and the rhyme “Red to yellow, kill a fellow, Red to black, venom lack,” but this rhyme does not work in South America.

DEFENSIVE STRATEGIES

Snakes have an array of defenses to avoid detection or warn off predators. Many snakes are highly camouflaged or cryptically patterned to enable them to hide in leaf litter or vegetation. Vinesnakes (Oxybelis, Ahaetulla, and Thelotornis) really do look like vines, while the head of a Gaboon Viper (Bitis gabonica) resembles a large dead leaf, and the rest of its Persian carpet patterning serves to break up its outline for both predator and prey alike. A few nocturnal snakes, such as rainbow boas (Epicrates), have iridescent body scales that shimmer in daylight and may also break up their outline when approached by a potential predator. American coralsnakes (Micrurus and Micruroides) are brightly banded red, yellow, and black, advertising that they are dangerous and should be left alone, a pattern mimicked by some harmless snakes to avoid interference.

Some snakes go in for big visual threat displays. Examples include the cobras (Naja), with their hooding; the Boomslang (Dispholidus typus), which inflates its neck to expose the contrasting colors of its interstitial skin; and the Black Mamba (Dendroaspis polylepis), with its wide-mouth gaping, exposing the black interior. Other snakes rely on auditory warnings, such as the buzzing tail of a rattlesnake (Crotalus), the sawing sound made by a carpet or saw-scale viper (Echis) as its continual motion causes its serrated keeled dorsal scales to rub together, or the loud hissing of a Russell’s Viper (Daboia russelii), Puff Adder (Bitis arietans), or Bullsnake (Pituophis catenifer sayi).

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The Cape Twigsnake (Thelotornus capensis) inflates its throat to expose the interstitial skin, making itself look larger and more threatening to potential predators.

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The Zebra Spitting Cobra (Naja nigricincta, above left) spreads a hood as a warning that it is dangerous, and if that fails it will send twin jets of venom into the eyes of its perceived enemy.

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The Western Diamondback Rattlesnake (Crotalus atrox,) avoids confrontations with enemies by vibrating its rattle vigorously. Every time the rattlesnake sheds its skin it adds another interlocking link to the rattle as the cross-section above illustrates. The oldest links are at the tip.

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If escape is an option, then few snakes have a better method than the Paradise Flying Snake (Chrysopelea paradisi), which can flatten its entire body into a concave parachute, so that it simply glides away from the threat when it leaps from a tree. Still other snakes pretend to be something they are not, mimicking the body shape, patterning, or behavior of highly venomous coralsnakes, cobras, or vipers—the Aesculapian False Coralsnake (Erythrolamprus aesculapii), Large-eyed Mock Cobra (Pseudoxenodon macrops), and Northern False Lancehead (Xenodon rabdocephalus) all employ this defensive measure.

One of the strangest ways to avoid predation is to play dead, a behavior known as thanatosis. American hognose snakes (Heterodon), European grass snakes (Natrix), and the South African Rinkhals (Hemachatus haemachatus) all play dead when they feel threatened. The last of these also has another defense in its armory—it is a spitting cobra capable of sending jets of painful cytotoxic venom into the eyes of an enemy, effectively blinding it while the cobra makes good its escape. This is probably the only instance where a snake’s venom has evolved for defense rather than hunting.

Another very strange defense measure is cloacal popping. Some coralsnakes (Micruroides and Micrurus) and hooknose snakes (Ficimia and Gyalopion) use this technique, forcefully and noisily expelling air from their cloacas.

HUMAN THREATS AND CONSERVATION

Humans have probably persecuted snakes for centuries, either killing them out of fear or harvesting them in unsustainable numbers for their skins, their meat, or their gall bladders, an apparently essential ingredient in an eastern tonic for failing libido in men. And of course snakes suffer from the same indirect threats to their survival as other animals, habitat destruction, fragmentation, and alteration. While some snake species have slipped into extinction through the agencies and actions of man, others have been saved by the intervention of conservation bodies, captive breeding, and educational campaigns aimed at teaching villagers or islanders to not only live alongside their serpentine neighbors, but also be proud of them and protect them.

American and European zoos have been actively engaged in a captive breeding program for the endangered Aruba Island Rattlesnake (Crotalus durissus unicolor), a small, pastel-colored subspecies of the large Tropical Rattlesnake, the aim being to bolster the population in the small desert center of its island. Two extremely primitive, endemic, egg-laying, split-jaw snakes, only distantly related to any other snakes on Earth, used to live on tiny (2/3 sq miles/1.69 km2) Round Island in the Indian Ocean, until seafarers introduced goats and rabbits to the island. The invasive mammals devoured the vegetation and then the rain washed the soil into the sea, and with it went the Round Island Burrowing Boa (Bolyeria multocarinata). The other species, the Keel-scaled Boa (Casarea dussumieri) was more fortunate, it was rescued by the Jersey Wildlife Preservation Trust ( JWPT) who, working with the Government of Mauritius, have brought the species back from the brink so when the island has been restored it is hoped the species can go home. Sadly the Burrowing Boa was declared extinct by the IUCN in 1975.

The JWPT and other conservation organizations have been behind the recoveries of Caribbean snakes such as the Antiguan Racer (Alsophis antiguae), Great Bird Island Racer (A. sajdaki), and the Jamaican Boa (Chilabothrus subflavus). Snakes might not be everybody’s “cup of tea” but that does not mean that they do not need conservation. And conserving snakes is actually beneficial to mankind, snakes are nature’s rat catchers, eating the rodents that carry disease and devour our crops.

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Snakes are rarely a vote winner when it comes to popularity, but conservation of snakes is important. Endangered species such as the Jamaican Boa (Chilabothrus subflavus) been saved from extinction by conservation organizations.

 

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