Eunectes notaeusYellow Anaconda

Geographic Range

Yellow anacondas occur in southern South America, including Paraguay, southern Brazil, northeastern Argentina, and Bolivia. (Burton, 1967)

Habitat

Yellow anacondas can be found in swamps and marshlands with slow-moving rivers or streams. They can also be observed in forests searching for large game, such as brocket deer or peccaries. During droughts they can be found using caves for shelter and along river banks in holes that retain water. During the rainy months, yellow anacondas can be found in flooded, treeless areas, where they hunt for aquatic species such as fish or caimans (Caiman). (Burton, 1967)

  • Aquatic Biomes
  • rivers and streams

Physical Description

Although yellow anacondas are much smaller than green anacondas (Eunectes murinus, the world's largest snakes) they do reach lengths of up to 4.6 meters (typical adult range 3 to 4 m). Yellow anacondas have yellowish-green scales with brown or blackish bands and overlapping spots that wrap around the entire body. This provides camouflage in murky water or in forest vegetation. Females grow longer than males and generally weigh more as well. Male yellow anacondas can reach up to 3.7 m in length while a female can reach a length of 4.6 m. (Mattison, 1986; Owen, 2004)

  • Sexual Dimorphism
  • female larger
  • Range mass
    40 (high) kg
    88.11 (high) lb
  • Average mass
    30 kg
    66.08 lb
  • Range length
    2.4 to 4.6 m
    7.87 to 15.09 ft
  • Average length
    3.7 m
    12.14 ft

Development

Females, after a 6 month gestation period, give birth to fully-developed live young. These young are immediately able to live on their own. Yellow anacondas seem to have indeterminate growth. (Leen, 1978)

Reproduction

For the most part, yellow anacondas are sequentially monogamous. Males become attracted to females when she produces pheromones released into the air. Males then follows the scent to the female and begin courtship. This courtship normally will take place in water and may last for quite some time. Yellow anacondas have been known to form breeding balls, consisting of one female and multiple males. These breeding balls have been known to stay together for up to a month. In the breeding ball, males compete for mating access to the female. Normally the largest male will win successfully outcompete other males. Larger males may successfully breed with more females as a result. (Grzimek, et al., 1971; Grzimek, et al., 1971; Mattison, 2007)

Yellow anacondas breed between April and May every year. Females incubate eggs in their bodies and give birth to already hatched young. The gestation period is 6 months, after which the female gives birth to from 4 to 82 young at a size of about 60 cm in length. After giving birth, female anacondas leave her young to defend for themselves. Young anacondas reach sexual maturity at 3 to 4 years old. (Mattison, 1995; Schmidt and Inger, 1982)

  • Breeding interval
    Yellow anacondas breed once yearly.
  • Breeding season
    Breeding occurs in April and May.
  • Range number of offspring
    4 to 82
  • Average number of offspring
    40
  • Average gestation period
    6 months
  • Range time to independence
    0 (low) days
  • Average time to independence
    0 days
  • Range age at sexual or reproductive maturity (female)
    3 to 4 years
  • Range age at sexual or reproductive maturity (male)
    3 to 4 years

Females provide significant resources to their young during incubation, but the young are independent at birth and there is no further parental care. (Mattison, 1995)

  • Parental Investment
  • no parental involvement
  • pre-fertilization
    • provisioning
    • protecting
      • female
  • pre-hatching/birth
    • provisioning
      • female
    • protecting
      • female

Lifespan/Longevity

Most mortality in yellow anacondas occurs as young, when they are smaller and vulnerable to predation. Once they reach adult sizes, yellow anacondas have few natural predators. The typical lifespan for yellow anacondas in the wild is from 15 to 20 years. In captivity yellow anacondas can live up to 23 years. Humans greatly influence the lifespan of yellow anacondas in the wild, as poaching has decreased the number of yellow anacondas to a dangerously unstable level. (Leen, 1978; Simon, 1992)

  • Range lifespan
    Status: captivity
    23 (high) years
  • Typical lifespan
    Status: wild
    15 to 20 years

Behavior

Yellow anacondas are strictly solitary, found only with other yellow anacondas for mating. Yellow anacondas may spend up to several months in courtship and mating, but separate once mating is complete. Most of their time is spent in aquatic habitats, hunting prey, although they venture onto land for mating, moving to other water bodies, or hunting occasional terrestrial prey. In times of drought yellow anacondas actively seek swamps and marshes with enough water in which to hunt. They are considered timid snakes and normally try to escape from predators, such as humans, but they will defend themselves when threatened. (Crompton, 1893; Leen, 1978)

Home Range

No information is available on home range size. Yellow anacondas do not seem to defend territories. (Simon, 1992)

Communication and Perception

Yellow anacondas are solitary animals, except in breeding season. Females attract mates through pheromones. Male anacondas will follow this pheromone trail and, once the potential mates encounter one another, they communicate by rubbing one another and proceed with courtship. All anacondas (Eunectes) have heat-sensing pits located along their mouths. These pits are used to find prey by detecting body heat given off by warm blooded animals. Like most snakes, yellow anacondas do not hear well, although they can pick up vibrations through their jaws. Yellow anacondas, like most snakes, rely heavily on their fork-like tongues and chemosensation to navigate their environment and help find prey. The tongue is flicked in and out of the mouth to taste the air, chemicals collected by the tip of the tongue are deposited in the vomeronasal organ on the top of the mouth. (Mattison, 2007)

Food Habits

Yellow anacondas are generalist carnivorous, preying mainly on animals found in wetland and riparian areas throughout their range. Their diet consists of birds, bird eggs, small mammals, turtles, lizards, occasional fish or fish carrion, and caimans. Wading birds may be their most common prey in some areas. They can reach sizes sufficient to take larger prey, such as brocket deer, peccaries, or capybaras. Yellow anacondas are considered ambush hunters and constrictors. They lay in wait in the water or in vegetation and strike at prey that pass. When prey are grabbed, they begin to wrap their body around the prey and begin constriction. With each exhalation of the prey, the constrictor can squeeze tighter, eventually causing asphyxiation. They may also pull the prey under water during constriction. Yellow anacondas then swallow prey head first by unhinging their jaws, as do other snakes. Along with their incredible jaw flexibility, yellow anacondas have more than a 100 recurved teeth that help to hold and swallow prey. Their digestive system is relatively slow and yellow anacondas may eat only every few days or months, depending on the size of their last prey item. Like other snakes, yellow anacondas can survive long periods without prey. In the wild most predation occurs from June to November, during the relatively dry periods when wetlands areas have shrunk. (Linley, 1993; Strussmann, 1997; Linley, 1993; Parker, 1963; Strussmann, 1997)

  • Primary Diet
  • carnivore
    • eats terrestrial vertebrates
  • Animal Foods
  • birds
  • mammals
  • reptiles
  • fish
  • eggs
  • carrion

Predation

Adult yellow anacondas have no natural predators. Humans are their main predators and they are hunted for their skin, for the zoo and pet trade, persecuted out of fear, and their habitats are destroyed. Predators of juvenile yellow anacondas include crab-eating foxes (Cerdocyon thous), tegu lizards (Tupinambis merianae), caimans (Caiman crocodilus), and larger anacondas (Eunectes). In order to avoid predation, young anacondas are camouflaged, as their dark-spotted patterns hides them in the vegetation. ("Anaconda", 1971; Parker, 1963)

  • Anti-predator Adaptations
  • cryptic

Ecosystem Roles

Adult yellow anacondas are keystone species; they are one of the top predators in the ecosystems they inhabit. Yellow anacondas influence the number of prey animals, which influences the populations of other prey animals and predators. Ticks from the family Ixodidae are found on yellow anacondas. However, yellow anacondas produce an odor that deters ticks from attaching themselves. ("Anaconda", 1971)

Commensal/Parasitic Species

Economic Importance for Humans: Positive

Yellow anacondas are hunted for their skin to make merchandise such as purses, shoes, and belts. Yellow anacondas are also taken for the pet trade. However, anacondas are unpredictable and dangerous and few people take on the challenge of keeping an anaconda as a pet. Yellow anacondas are kept by zoos, where they are a popular attraction. People are intrigued by these species and also terrified by them. ("Anaconda", 1971)

  • Positive Impacts
  • pet trade
  • body parts are source of valuable material

Economic Importance for Humans: Negative

Yellow anacondas are large and aggressive snakes that can inflict damage on humans if approached or threatened. They may even pose a predation risk to small children, but attacks on humans by yellow anacondas are exceptionally rare. ("Anaconda", 1971)

  • Negative Impacts
  • injures humans
    • bites or stings

Conservation Status

Yellow anacondas are on the IUCN Red List as threatened due to poaching. It is illegal to hunt yellow anacondas in most of South America. This law has helped population numbers to increase, but pet trading and zoos still threaten their survival. ("Anaconda", 1971)

Contributors

Tanya Dewey (editor), Animal Diversity Web.

Kelly Colthorpe (author), Radford University, Karen Francl (editor, instructor), Radford University.

Glossary

Neotropical

living in the southern part of the New World. In other words, Central and South America.

World Map

acoustic

uses sound to communicate

arboreal

Referring to an animal that lives in trees; tree-climbing.

carnivore

an animal that mainly eats meat

carrion

flesh of dead animals.

chemical

uses smells or other chemicals to communicate

cryptic

having markings, coloration, shapes, or other features that cause an animal to be camouflaged in its natural environment; being difficult to see or otherwise detect.

diurnal
  1. active during the day, 2. lasting for one day.
fertilization

union of egg and spermatozoan

freshwater

mainly lives in water that is not salty.

heterothermic

having a body temperature that fluctuates with that of the immediate environment; having no mechanism or a poorly developed mechanism for regulating internal body temperature.

indeterminate growth

Animals with indeterminate growth continue to grow throughout their lives.

infrared/heat

(as keyword in perception channel section) This animal has a special ability to detect heat from other organisms in its environment.

iteroparous

offspring are produced in more than one group (litters, clutches, etc.) and across multiple seasons (or other periods hospitable to reproduction). Iteroparous animals must, by definition, survive over multiple seasons (or periodic condition changes).

keystone species

a species whose presence or absence strongly affects populations of other species in that area such that the extirpation of the keystone species in an area will result in the ultimate extirpation of many more species in that area (Example: sea otter).

marsh

marshes are wetland areas often dominated by grasses and reeds.

native range

the area in which the animal is naturally found, the region in which it is endemic.

nocturnal

active during the night

ovoviviparous

reproduction in which eggs develop within the maternal body without additional nourishment from the parent and hatch within the parent or immediately after laying.

pet trade

the business of buying and selling animals for people to keep in their homes as pets.

pheromones

chemicals released into air or water that are detected by and responded to by other animals of the same species

polygynandrous

the kind of polygamy in which a female pairs with several males, each of which also pairs with several different females.

polygynous

having more than one female as a mate at one time

rainforest

rainforests, both temperate and tropical, are dominated by trees often forming a closed canopy with little light reaching the ground. Epiphytes and climbing plants are also abundant. Precipitation is typically not limiting, but may be somewhat seasonal.

riparian

Referring to something living or located adjacent to a waterbody (usually, but not always, a river or stream).

seasonal breeding

breeding is confined to a particular season

sedentary

remains in the same area

sexual

reproduction that includes combining the genetic contribution of two individuals, a male and a female

solitary

lives alone

swamp

a wetland area that may be permanently or intermittently covered in water, often dominated by woody vegetation.

tactile

uses touch to communicate

terrestrial

Living on the ground.

tropical

the region of the earth that surrounds the equator, from 23.5 degrees north to 23.5 degrees south.

vibrations

movements of a hard surface that are produced by animals as signals to others

visual

uses sight to communicate

References

1971. Anaconda. Pp. 45 in M Burton, ed. The World Encyclopedia of Animals, Vol. 1, 1 Edition. New York: World Publishing.

Ardley, N., D. Stephen, A. Wheeler. 1975. The Boidae (boas) and Pythonidae (pythons). Pp. 425-426 in A Waterson, ed. Encyclopedia Of The Animal World, Vol. 1, 1 Edition. New York: Larousee.

Burton, M. 1967. Reptiles (Class Reptilia). Pp. 320 in R Murphy, ed. The Larousse Encyclopedia of Animal Life, Vol. 1, 1 Edition. New York: McGRAW-HILL BOOK COMPANY.

Crompton, J. 1893. The Snake. New York: Nick Lyons Books.

Grzimek, B., Z. Vogel, H. Wendt. 1971. Boids. Pp. 378 in H Hediger, ed. Grizimek's Animal Life Encyclopedia, Vol. 1, 1 Edition. New York: Van Nostrand Reinhold Company.

Leen, N. 1978. Snakes. New York: Holt, Rinehart and Winston.

Linley, M. 1993. Snakes. New York: Thomson Learning.

Mattison, C. 1986. Snakes Of The World. New York: Facts On File Publications.

Mattison, C. 2007. The New Encyclopedia of Snakes. New Jersey: Princeton University Press.

Mattison, C. 1995. Boidae (Boas ande phythons). Pp. 200 in C Mattison, ed. The Encyclopedia of Snakes, Vol. 1, 1 Edition. New York: Facts on File.

Owen, W. 2004. Snakes:Reptiles. Pp. 397 in J Flew, L Humphries, eds. The Encyclopedia of Animals, Vol. 1, 1 Edition. Los Angeles: Unioversity of California Press.

Parker, H. 1963. Snakes of The Wolrd: Their Ways and Means of Living. New York: Dover Publications.

Schmidt, K., R. Inger. 1982. Boas and Pythons (Family Boidae). Pp. 233-241 in The Audubon Society Encyclopedia of Animal Life, Vol. 1, 1 Edition. New York: Crown Publishers.

Simon, S. 1992. Snakes. 1992: HarperCollins Publishers.

Strussmann, C. 1997. Feeding habits of the yellow anacond. Eunectes notaeus Cope,1862, in the Brazilian Pantanal, 5/1: 35-52.