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When does the snake wag its tail and why does it hold back for a year from defecating

Natalie Angier New York Times

The viper family is a large, ancient and diverse family of snakes that includes more than 200 species that are spread over all the continents of the world, except Australia.

Some of them, for example the innkeepers, are pit vipers. These are characterized by special dimples located between the nostril and the eye, which are sensitive to infrared radiation. In this way, the snake can receive heat signals from both crazy and prey, and get a thermal image of the area, like in night vision devices. Many of the vipers also have complex "rattles" - sort of nail-like plates at the end of the tail, which can emit a loud warning at a rate of 50 clicks per second. And all vipers are equipped with retractable hollow venom teeth, the seal of the vipers, through which the snake injects the venom.

While most snakes lay eggs, most viper snake species spawn live offspring. Hence their name - viper: a combination of the Latin words vivo, life, and partus, birth.

Recently, a new book describing the fascinating world of vipers was published in the USA, "Biology of the Vipers" published by Eagle Mountain. Several dozen reptile experts present a variety of surprising, amusing and discouraging findings about vipers.

Dr. Harry Green and his colleagues from Cornell University describe, for example, cases of parental behavior among the black-tailed deer and the pygmy deer, which contradicted all their assumptions. "We expected that after spawning, the mothers would crawl in one direction and the offspring in another," said Dr. Green, "but instead we saw the mother huddle with her offspring day after day, or guard the entrance to the den with the offspring inside."

The researchers hypothesize that parental behavior has evolved in some viper species, along with the delay in shedding the skin. While most young snakes shed their skin immediately after they are born, the young viper snakes, relatively large compared to other species, shed their skin only when they are about ten days old. While shedding their skin, their vision blurs, they are particularly sensitive to water loss, and are very vulnerable. Hence the need for the mother's close supervision.

The traditional perception holds that snakes are not particularly smart - or as one of the reptile researchers defined it, "they are quite low on the intelligence scale". But Dr. Randall Reiserer, from Vanderbilt University in Nashville, Tennessee, actually found evidence that vipers can actually learn from their experience, and adapt their hunting strategies to new circumstances.

Reiserer collected 10 young vipers of the Massasauga species for his laboratory, some from swamp areas in the eastern US and others from the deserts of Arizona. In general, Eastern Masasauga snakes lure fast-moving frogs with undulating movements of their tails, mimicking a worm. But when they spot a slow lizard, they don't move their tail but continue to crawl on their belly until they attack.

Western Masasauga snakes, on the other hand, have to deal with nimble desert lizards, which they lure with a quick flick of the tail, and ignore the few frogs in the area because they are too poisonous.

Razerer showed that, despite their differences, western vipers can learn to hunt like the eastern ones - by wagging their tails to hunt frogs and attack slow lizards, while the eastern vipers can be taught to wag their tails to hunt lizards and avoid frogs.

In addition to behavioral findings, reptile experts also continue to be impressed by the physiology of vipers. Dr. Akira Mori and his colleagues, from Kyoto University, describe in the book the hypothermic talent of the hime-habu, a small viper snake active at night, which does not hide from the cold. The snake is found in Okinawa and other islands in the Ryukyu Archipelago.

Being cold-blooded, snakes depend on heat from the outside to warm their bodies, to move, to hunt and to digest their food. When the temperature drops below 10 degrees Celsius, most snakes become practically paralyzed. If there is food in their stomachs, they must rumen because they are unable to digest it, and they may die from the rotting of the meat inside them. Snakes living in cold climates hibernate with their stomachs empty.

But the hime-habu has developed the ability to continue eating for short periods of time from December to March, even when temperatures drop below 10 degrees. This ability, which other vipers do not have and probably not other snakes either, allows the hime-habu to enjoy a rich food source that is not used by competing reptiles - two species of frogs, which gather en masse near springs in the mountains for several days, for breeding purposes.

Another interesting phenomenon in several viper species is described by Dr. Harvey Lillywhite and his colleagues from the University of Florida in Gainesville. They call it "adaptive constipation". Among some of the ground-dwelling vipers defecating is an extremely rare event, they report. The Gabonese vipers (Bitis gabonese) in Africa, for example, can go an entire year or more without defecating, even while continuing to eat rodents regularly. These vipers probably hold the record in the animal kingdom. In contrast, semi-deciduous vipers (which also live on trees), defecate in a way we are more familiar with, usually a few days and even a few hours after the meal.

Ground-dwelling vipers store so much excrement, the researchers calculated, that it may constitute up to 20% of their body weight. Most of the feces is concentrated in the back of the body.

Dr. Lillywhite suggests that ground-dwelling vipers keep their excrement because it helps with their stability. It helps anchor the lower part of their body to the ground, and allows the snake to move its head towards the prey with great speed and precision. The tree-dwelling vipers, on the other hand, can use the branch to stabilize their bodies.

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