Green Anaconda - Eunectes murinus

Green Anaconda - Eunectes murinus Class – Reptilia Order – Squamata Family – Boidae Genus – Eunectes Species – murinus Status – CITES, Appendix II Life Span - Anacondas can live into their thirties. Conservation Notes - At present, all South American countries prohibit trade regarding the anaconda. However, some of these countries will allow live export for zoos and research in a limited capacity. Presently, CITES, PROFAUNA and The Wildlife Conservation Society jointly are conducting the first field study of the anaconda. Description The Green Anaconda (Eunectes murinus) is considered by many to be the largest snake in the world. These snakes may reach lengths of over 29 feet. There are many exaggerated stories and legends about Anacondas being much longer, but they have never been confirmed. There are descriptions by travelers of Anacondas up to 140' long. These claims have never been substantiated. Stories about enormous man-eating snakes make for great horror movies, but they are not the reality. An 'Urban Legend' circulating by way of e-mail claims that an Anaconda ate a South American boy while he slept. http://www.snopes.com/horrors/animals/anaconda.htm This link supposedly includes 'actual' photos of the boy inside the snake and also after the snake was cut open. It was obviously a hoax. The first two pictures show a large common boa, which had consumed a large prey item. The third, showing the boy inside the snake, does not match the other two and was apparently set up. Many things encourage the folklore surrounding Anacondas. A skin of a freshly killed Anaconda may stretch a full 30% in length, as in all snakes, while being tanned. This ability obviously lends support to the typical hunter's story of Amazonian giants. A petroleum geologist in eastern Columbia encountered the Anaconda thought to be the largest specimen recorded in 1944, measuring 37-1/2 feet in length. Because of the exaggerated stories and mystery surrounding these snakes, actual maximum length and size measurements are difficult to ascertain. The Anaconda is arguably the heaviest snake in the world and the longest in the western hemisphere but it is not considered the longest in the world. The Reticulated Python (Python reticulates), which can attain a length of 33 feet, is generally accepted as the longest snake. An Anaconda may reach a length of 30 feet, but the average is 18 feet. However, a 20-foot Anaconda will weigh more than a 33-foot python. An adult Anaconda may reach 200 pounds and can measure more than 12 inches in diameter. The female typically outweighs the males. In fact, Anacondas show the largest sexual size dimorphism found in any tetrapod. Anacondas also present an amazing change in size from birth to adulthood. An adult Anaconda can weigh 500 times more than it's hatchling size. This is significantly higher than the increase found in any other species of snakes. The Tamil word for Anaconda is "anaikolra" which means "elephant killer". The early Spanish settlers referred to this snake as "matatoro" or "bull killer". The Anaconda is also referred to as a 'water boa' due to its tendency to live in or near the swamps and back river systems. In water, they can stay completely submerged for 10 minutes. They often lay submerged waiting for prey. They are agile swimmers but sometimes prefer to let the river's current carry them downstream with only their nostrils above the watery surface. Once they are satisfied with the change in scenery, they simply drift to the river's edge. Anacondas are more often found in swamps and calmer waters than in swift-moving rivers. They actually tend to be nocturnal which adds even more to their mystery on a dark night in the swamp. Due to their size, they appear sluggish on land or hanging in a tree but in water they are capable of surprising speed on the surface and underneath. The green Anacondas are dark green in color with black oval-shaped patterns on their backs. Their sides have spots with yellow centers. Because of their coloration they are able to remain hidden in the swampy habitat. The Anaconda's eyes and nostrils are on the top of their heads, enabling them to breathe and see their prey while hidden under the water. Their anal glands emit a musk which most creatures find unpleasant. It is poisonous to many small organisms and may offer some level of protection from external parasites. It is not uncommon for Anacondas to become infested with ticks when they spend time out of the water. There are spurs on either side of the anal scales, which is typical of boidae. The males have larger and thicker spurs than the females. These are used in courtship, mating and combat. Feeding Habits All Anacondas are in the boidae family and the largest is the green Anaconda (Eunectes murin). This is a true constrictor. These specimens usually utilize a swift bite to hold their prey followed by a coiling of a loop or two around the main body. Once these loops are in position, the snake will steadily constrict with incredible strength to suffocate the victim. The sheer strength of the Anaconda immediately restricts the breathing of the victim. With each exhale of air the lung slack is removed to prevent further inhaling. In just a few moments, the prey is ready to consume. Another effective technique used by the Anaconda is simply holding the victim under water until drowning occurs, although this is less efficient and more time consuming. The prey is seldom crushed although there is ample ability to do this. As with all snakes, the suffocated meal is swallowed whole and in one piece. Usually the head is swallowed first as the limbs tend to fold conveniently in and smoothly move down toward the stomach as swallowing occurs, compressing the animal with each surge forward of the muscles. The Anaconda, like all snakes, can swallow prey much larger than the size of its mouth since an elastic ligament connects its upper and lower jaw. Green Anacondas typically feed on large rodents, tapirs, capybaras, deer, peccaries, fish, turtles, birds, sheep, dogs and aquatic reptiles (mainly caimans). They have been known to occasionally prey on jaguars and attacks on humans, although rare, have been confirmed. Younger Anacondas feed on mice, rats, chicks, frogs and fish. Anacondas, like all snakes have a very low metabolism. They must rest for several days until a large meal is digested. If a meal is particularly large, Anacondas may not need to eat again for several months. There is a record of an Anaconda in captivity going two years without eating. Range and Habitat The Anaconda is found throughout tropical South America, east of the Andes and mainly in the Amazon and Orinoco Basins. It is also found in Trinidad, and a smaller species, the Paraguay Anaconda, occurs in the rivers of the southern part of the continent. The yellow Anaconda can be found as far south as Argentina. Unlike his cousin, the green Anaconda, the yellow Anaconda (Eunectes notaeus) averages 10 - 12 feet in length. The habitats of Anacondas are swamps, marshes, brush covered banks of rivers and streams. The Anaconda prefers to be in the water, but they do spend some time on land in shallow caves by the water's edge, or in riverbank trees basking in the sun. Reproduction Anacondas are solitary animals except during mating season. They typically have a territory that they remain in. The beginning of the rainy season triggers mating behaviors in Anacondas. This can last for several months. The males will follow the scent of the female, who emits pheromones. It is unclear whether they leave a trail as they move about or if the scent becomes airborne. There is supporting evidence for the airborne idea. Females tend to remain in one place during the breeding period and males approach her from all directions. In addition, the males will flick their tongues to pick up the scent. The entire mating ritual takes place in the water. The male will wrap himself around the female and rub his spurs against her cloacal area, stimulating her to copulate with him. This makes an audible hissing sound. The female then raises her body up to meet the male's hemipenes to complete the copulation. Biologist Jesus Rivas has been studying green Anacondas in the wild since 1992. He has discovered some previously unknown mating habits. Among his unusual findings: "breeding balls," consisting of 2 to 12 males coiled around one female for as long as four weeks. Breeding balls, which Rivas calls "slow-motion wrestling matches," provide researchers with the opportunity to capture the males and remove them to the laboratory for further study. The female is allowed to go free to attract other males. Anacondas are viviparous, which means that the eggs are incubated internally and the young are born alive. The gestation time for Anacondas is approximately 6 months. The average is around 20-30 hatchlings, but as many as 100 births from one female have been observed. They are only about two feet long and are very vulnerable to predators at this stage. They can swim at birth and begin to hunt immediately. There is no parental care by the mother. They will reach sexual maturity at approximately 3-4 years of age. The growth will continue throughout their lives, but will slow down at maturity. Future of the Green Anaconda The greatest threat to the Anaconda is man. Most local people kill these snakes on sight, out of the fear that they are man-eaters. In most instances, if an Anaconda senses humans in the area, it will retreat in another direction. Human death by Anaconda is quite rare. Habitat destruction is another problem that the Anaconda faces. According to Jesus Rivas, The green Anaconda is the largest snake in the world. Although famous, very little is known about its life history. Until I began my research, no field studies had been carried out on the species. Due to the skin trade its numbers have declined in places where they are not protected. Habitat degradation and the expansion of the agricultural frontier are also threatening the populations of this formidable reptile. In an effort to protect the species I began the Anaconda Project in 1992, with the aim to learn the basic aspects of the Anaconda's biology in order to create guidelines for its protection and possible management (3)
	"Predatory attacks of green anacondas (Eunectes murinus) on adult human beings." Large constrictors snakes are potentially dangerous to people due to their size and strength (Branch and Haacke 1980). However, there are no documented attacks by green anacondas (Eunectes murinus) on humans. The lack of documentation may be due to low human population in areas where anacondas are common, and to the nature of their behavior and the habitat where they live. In this note I document predatory strikes by green anacondas on two of my field assistants while conducting field research on green anaconda in the Venezuelan llanos. The first attempt was by a large female (Lin; 54 kg, 5.04 m total length) that had had a serious mouth infection at the time I captured it and implanted a radio-transmitters in it. Two months after implantation, my assistant (female, 1.56 m and 55 kg) followed the transmitter signal with the intention of assessing the status of the snake’s infection. The snake was in a shallow channel, approximately 80 cm deep, which was partly covered by emergent aquatic vegetation (Eleocharis sp, Cyperacea). Without being seen, the snake emerged from water striking and grabbing her by the knee. Fortunately, the pants tore, and the snake did not get a firm hold by which to drag my helper into the water. The snake immediately struck again with her mouth open to about 180 degrees, this time at a height level with my helper’s waist. However, her prompt retreat resulted in an unsuccessful attack. The other event was on another of my helpers (male, 1.74m 57 kg) while we were looking for snakes in a river covered by aquatic hyacinth (Eichhornia ssp). After we walked by the snake without detecting it, the snake followed my helper, tongue flicking at him for approximately 2.5 m, raising itself up to 25 cm above the aquatic vegetation. The snake was seen and filmed by a photographer behind us who warned us about the snake. I managed to grab the snake by mid-body just as it struck to my helper who in turn jumped backwards. Both, me pulling the snake backwards and he moving out of reach made the snake fail and snap into the air (Figure 1a to 1f, extracted from the tape). Upon catching and subduing the animal (Pen), She measured 445 cm in total length and 39 kg in weight. The overall appearance of the snake was healthy but very thin. I believe that both attacks were predatory attempts of the snakes on my helpers. In the first instance the following evidence suggests that the snake must have been foraging when attacked the researcher: First, she had not eaten during the two months she had been radio-tracked, and probably longer, due to the oral infection. Second, eight daysbefore the incident the snake thoroughly tongue flicked at me (male, 1.77 cm, 83 kg) in a similar situation but lost interest after approximately 5 min (perhaps estimating that I was above her prey-size range). Finally, four days after the incident I saw the snake with a distended midsection that indicated a recent meal. Lin’s attack is unlikely to have been defensive. In my experience catching anacondas of all sizes, I have found that large individuals are very unlikely to attack when disturbed. Indeed, to the present I have caught and processed more than 120 animals larger than 4 meters and none tried to bite until I (or one of my helpers) had either, dragged the animal out of the water by its tail, or secured a firm grip on the animal’s neck (Rivas 1999). Large individuals tended to swim away when disturbed. Recaptured animals are, if anything, even more skittish than naive ones and try to escape as soon as they detect the proximity of the researchers. Thus, the proximity of the researcher is unlikely to have induced a defensive strike. Anacondas can capture prey as large as adult capybaras, adult white tailed deer and full grown spectacled caiman (Rivas 1999); consequently, a prey as heavy as 55 kilos (the weight of the first target) is within the range of prey sizes that a snake as large as Lin could take. Given the snake’s later behavior (which was most likely foraging), the size of both snake and potential prey, along with the fact that the researcher had not disturbed the snake, (the snake struck while submerged under enough water for a safe escape), I consider that it was a predatory the strike. Lin was being followed by telemetry, thus enhancing the number of times she encountered a human being. This artificially high encounter rate with people might have exceeded the threshold of abundance that makes a potential prey item profitable despite the high risk of attacking a large potentially dangerous prey (Stephen and Krebs 1986). The second event was performed by large animal that was fairly thin for her size (Rivas 1999). Pen was performing predatory tongue-flicking directed towards the person following him for a relatively long distance. Given the date of this event (March) it is likely the snake had given birth the year before (November to December) and was hence in need of a large meal to recover from her reproductive investment. She was probably in a large energetic deficit and taking the risk of attacking a large prey was a good way to overcome it. The prey/predator mass ratio of this event (1.46), while impressive, falls within the reported prey/predator ratios reported for other snakes (Greene 1992). Both attacks were on people that were looking for anacondas in places that people often do not walk, We had been staying in these places for longer than people normally do, when they use these areas at all. Thus, both occurred after a particularly high exposure. Although anacondas are not "man-eaters" by nature, they are generalists and will take any prey that they can subdue and swallow. Thus, the potential exists for anacondas to prey on people. Rivas, J. A, 1999. Predatory attacks of green anacondas (Eunectes murinus) on adult human beings. Herptological Natural History. 6(2): 158-160.