Big anaconda
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Great anaconda ( Eunectes murinus ) |
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| Eunectes murinus | ||||||||||||
| ( Linnaeus , 1758) |
The green anaconda ( Eunectes murinus ) is a species of snake from the family of boas (Boidae), where it is in the subfamily of the constrictor snakes found (Boinae). She is one of the largest snakes in the world. Large anacondas inhabit the tropics of South America. The species is closely tied to water and inhabits large bodies of water of all kinds.
description
The great anaconda is one of the largest giant snakes in the world, but reliable data on the maximum length of living or newly dead individuals are not available. According to Dirksen, the longest known skin of a large anaconda, probably not stretched after death, is about 8.9 m long. This skin was missing the head and the tip of the tail, so the animal would have had a total length of over 9 m. There is also no reliable information on the maximum weight, exceptional specimens “ should be able to weigh over 200 kg. “The verified values of larger samples are considerably lower, with the great anaconda showing extreme gender dimorphism in terms of body length and weight . Females are on average larger and considerably heavier than males. In Venezuela , sexually mature males measured in a study had overall lengths of 1.88–3.34 m, a mean 2.63 m and weighed 2.5–14.3 kg, mean 7.0 kg; Females reached 2.43–5.17 m, a mean 3.70 m and weighed 9.3–82.5 kg, meanwhile 32.6 kg. The largest female caught by the same authors in another study weighed 97.5 kg.
The species is very strongly built, the body is approximately round in cross section. The head is relatively small and only slightly separated from the neck. Compared to other species of the subfamily Boinae, the tail is relatively long, making up about 15% of the total length. The eyes and nostrils are located high on the head in adaptation to the aquatic way of life.
The number of supralabials can be between 14 and 19, the lower jaw shows 18-25, on average 21 infralabials . The number of abdominal scales ( ventral shields ) varies between 239 and 266 and averages 249, that of the subcaudalia between 55 and 78 (average 68) and the number of dorsal rows of scales in the middle of the body is 55-74, with an average 63.
The basic color of the great anaconda varies between brown and olive green. On the back the species shows oval to round black spots, which can have a lighter center and vary greatly in number. On the side she has eye spots with yellow centers. Behind the eyes there are two parallel black stripes that delimit a variable white, orange or red field; however, this field can also have the same color as the body. The underside is creamy white to light yellow, the belly scales are irregularly spotted with black; these spots can be designed as paired lines. The tongue is black.
distribution and habitat
Of all anacondas, the great anaconda is the most common. It occurs east of the Andes in the entire northern lowlands of South America from the Orinoco and Amazon river systems to the south to the central Rio Paraná and Río Paraguay . The species is closely tied to water and inhabits water-rich habitats of all kinds with dense vegetation, especially swamps, still waters and slow-flowing rivers.
behavior
The great anaconda moves rather sluggishly on land. In waters where it spends a lot of time and from which it also hunts, it can reach higher speeds. She often moves her body just below the water surface and only her head above the waterline. It was also observed that the snake can dive underwater for some time. It moves meandering on the bottom of the water and, as on land, orientates itself with the help of its forked tongue.
Systematics
No subspecies are recognized for the species today. According to Dirksen , a subspecies described earlier ( E. m. Gigas ) cannot be sufficiently differentiated from the nominate form.
Way of hunting and food
The species is a stalker; the main hunting method is evidently to wait motionless in the water until the prey comes within reach. It is very well camouflaged by its coloring. Like all giant snakes, the great anaconda then bites into the prey, wraps around it and thus brings its breathing (ventilation) and blood circulation to a standstill, which quickly leads to death. The prey is then devoured head first.
The food spectrum of the great anaconda includes all small to medium-sized vertebrates occurring in their habitat, i.e. fish , amphibians , reptiles , birds and mammals . However, depending on gender and size, the species shows clear food choices. Smaller specimens primarily eat birds; males do so throughout their lives. Females from a length of about 3 m and when they reach sexual maturity mainly prey on reptiles and mammals, presumably in order to be able to grow stronger and to meet the high energy requirements necessary for reproduction.
Systematic studies on the composition of the prey spectrum have apparently not yet been published; According to individual observations , the regular food of large females includes young capybaras , and young white-tailed deer , caimans and smaller conspecifics are also captured.
In particular, capturing capybaras is not without risk for the anaconda. In Venezuela, 35 out of 38 females examined had scars that were presumably due to bite wounds. In one case an anaconda was found eating a capybara with a large fresh flesh wound. In another case, an anaconda that had captured a 2.5 kg young capybara had apparently been killed by other capybaras.
Natural enemies
In the first year of life the mortality of the young animals is apparently very high; these are captured by big cats , caimans and larger conspecifics. Mortality decreases with increasing size. Adult anacondas hardly have any natural enemies.
Reproduction
The mating season varies depending on the geographical location; systematic studies on this are so far only available from Venezuela . Mating was found here after the beginning of the dry season from mid-March to late May. The mating mostly takes place in shallow water. When mating, the male wraps around the female with one or two loops on the back of the body. Often mating balls are formed , which consist of a female and several males that wrap around this female at the same time. In Venezuela, 1 to 13 males, on average 3.8 males, were found with one female; the number of males was positively correlated with the size of the females. Within these groups, the males try to get to the cloaca of the female for copulation by pushing other males aside; large males are much more successful at this. The great anaconda is polyandric , the females copulate with several males in a row, while the males apparently only copulate with one female per season.
The great anaconda is ovoviviparous . The young are born alive after a gestation period of six to eight months. The litter size obviously increases with the size of the female, as with many snake species. Four females three to four meters long gave birth to 18 to 30 young animals, 45 embryos were found in a 4.5 meter long female and the litter of a 6.3 m long female contained 72 juvenile snakes. The newly born young are usually 70 to 90 cm long and 150–400 g in weight.
Females invest heavily in their offspring; in Venezuela, the birth weight of all young animals together averaged 40% of the body mass of the female determined after birth. This high energy expenditure presumably means that the females only have young every second year.
Danger
Information on the risk is currently not available, the species is also not listed by the IUCN . In view of the large distribution area, however, the species should be safe.
literature
- L. Dirksen: On the knowledge of the anaconda species (Serpentes: Boidae: Eunectes). II. Eunectes murinus (Linnaeus, 1758). herpetofauna 22 (126), 2000: pp. 23-34.
- JA Rivas, MC Muñoz, GM Burghardt, JB Thorbjarnarson: Sexual size dimorphism and mating system of the Green Anaconda (Eunectes murinus). In: RW Henderson, R. Powell (Eds.): Biology of the Boas and Pythons. Eagle Mountain Publishing Company, Eagle Mountain 2007: pp. 312-325. ISBN 978-0-9720154-3-1
- JA Rivas, MC Muñoz, JB Thorbjarnarson, GM Burghardt, W. Homstrom, PP Calle: Natural History of the Green Anaconda (Eunectes murinus) in the Venezuelan Llanos. In: RW Henderson, R. Powell (Eds.): Biology of the Boas and Pythons. Eagle Mountain Publishing Company, Eagle Mountain 2007, pp. 129-138. ISBN 978-0-9720154-3-1
Web links
Individual evidence
- ↑ L. Dirksen: For the knowledge of the anaconda species (Serpentes: Boidae: Eunectes). II. Eunectes murinus (Linnaeus, 1758). In: herpetofauna 22 (126), 2000, p. 28.
- ↑ JA Rivas, MC Muñoz, GM Burghardt and JB Thorbjarnarson: Sexual size dimorphism and mating system of the Green Anaconda (Eunectes murinus). In: RW Henderson and R. Powell (Eds.): Biology of the Boas and Pythons. Eagle Mountain Publishing Company, Eagle Mountain 2007, p. 315
- ↑ a b c J. A. Rivas, MC Muñoz, GM Burghardt and JB Thorbjarnarson: Sexual size dimorphism and mating system of the Green Anaconda (Eunectes murinus). In: RW Henderson and R. Powell (Eds.): Biology of the Boas and Pythons. Eagle Mountain Publishing Company, Eagle Mountain 2007, p. 321
- ↑ L. Pizzato, OAV Marques, M. Martins: ecomorphology of Boine snakes, with emphasis on South-American forms. In: RW Henderson, R. Powell (Eds.): Biology of the Boas and Pythons. Eagle Mountain, pp. 35-48
- ↑ L. Dirksen: For the knowledge of the anaconda species (Serpentes: Boidae: Eunectes). II. Eunectes murinus (Linnaeus, 1758). In: herpetofauna 22 (126), 2000, p. 26.
- ↑ L. Dirksen: For the knowledge of the anaconda species (Serpentes: Boidae: Eunectes). II. Eunectes murinus linnaeus, 1758. In: herpetofauna 22 (126), 2000, pp. 23 and 25.
- ↑ JA Rivas, MC Muñoz, JB Thorbjarnarson, GM Burghardt, W. Homstrom and PP Calle: Natural History of the Green Anaconda (Eunectes murinus) in the Venezuelan Llanos. In: RW Henderson and R. Powell (Eds.): Biology of the Boas and Pythons. Eagle Mountain Publishing Company, Eagle Mountain., 2007: p. 131 and 135
- ↑ JA Rivas, MC Muñoz, GM Burghardt and JB Thorbjarnarson: Sexual size dimorphism and mating system of the Green Anaconda (Eunectes murinus). In: RW Henderson and R. Powell (Eds.): Biology of the Boas and Pythons. Eagle Mountain Publishing Company, Eagle Mountain., 2007: pp. 312-325
- ↑ L. Dirksen: For the knowledge of the anaconda species (Serpentes: Boidae: Eunectes). II. Eunectes murinus linnaeus, 1758. In: herpetofauna 22 (126), 2000, pp. 29-30
- ↑ JA Rivas, MC Muñoz, GM Burghardt, JB Thorbjarnarson: Sexual size dimorphism and mating system of the Green Anaconda (Eunectes murinus). In: RW Henderson, R. Powell (Eds.): Biology of the Boas and Pythons. Eagle Mountain Publishing Company, Eagle Mountain 2007, p. 318