Anacondas—Are They Shedding Some Secrets?

By An Awake! Staff Writer

I DON’T know about you, but big snakes fascinate me in a way that few other animals do. And if we’re talking about big snakes, we’re talking about anacondas, members of the animal family Boidae. Curiously, though, despite their huge proportions, little has been known about their behavior—that is, until recently.

In 1992, biologist Jesús A. Rivas and researchers of the New York-based Wildlife Conservation Society (WCS) began to study these giants for the first time ever in the wild. * When I read that this six-year-long field study, which was carried out in a swampy region of Venezuela, had revealed some new facts, I wondered what had been learned. Today I will try to find out.

About Names and Species

On a sunny afternoon, I leave my Brooklyn office and head for the WCS headquarters, located in New York City’s Bronx Zoo. I had already done enough research to know some facts about anacondas.

Strangely, the name anaconda may have originated far from the animal’s South American home. Some say that it comes from the Tamil words anai, meaning “elephant,” and kolra, meaning “killer.” Others think it comes from the Sinhala word henakandayā (hena, meaning “lightning,” and kanda, meaning “stem”). Likely the Sinhala words—originally used for pythons in Sri Lanka—were brought from Asia to South America by Portuguese traders.

Speaking of misnomers, even the anaconda’s official name, Eunectes murinus, is not exactly correct.  Eunectes means “good swimmer”—and that it is. But murinus stands for “mouse-colored.” For a snake with an olive-green skin, this name “does not seem really suitable,” notes one reference work.

There is one more thing to mention about the animal’s scientific names and divisions. Literature on anacondas usually states that there are two species of anacondas. One is the subject of this article—the green anaconda, or water boa, slithering mainly in the swamps of the Amazon and Orinoco basins and in the Guianas. The other is the smaller yellow anaconda (E. notaeus), a denizen of Paraguay, southern Brazil, and northern Argentina.

Meet an Expert

Here I am at the Bronx Zoo. This wildlife park, covering 265 wooded acres [107 wooded hectares], is home to more than 4,000 animals, including a dozen or so anacondas. Khaki-clad William Holmstrom of WCS’s Department of Herpetology (the study of reptiles) is here to meet me at the zoo’s entrance. Mr. Holmstrom—a 51-year-old New Yorker wearing glasses, a mustache, and a ready smile—is the collection manager of the zoo’s reptile department and has participated in the field study of anacondas in Venezuela. According to him, scientists now recognize the existence of a third species of anaconda (E. deschauenseei), an inhabitant of northeastern Brazil and coastal French Guiana. * This afternoon Mr. Holmstrom will be my expert guide.

It doesn’t take long to sense that my guide loves snakes the way others love poodles or parakeets. He tells me that from the time he was a child, his parents’ home housed salamanders, frogs, and the like. “Father liked them. Mother tolerated them.” Needless to say, Mr. Holmstrom took after his father.

Dazzling Dimensions and Drastic Differences

Inside the 100-year-old reptile house, the two of us stop in front of an enclosure that houses an anaconda. Although I am looking at an animal that I anticipated seeing, I still can’t suppress my amazement. I marvel at its sheer size and bizarre proportions. Its blunt-nosed head, bigger than a man’s hand, is dwarfed by the bulky body attached to it. My guide tells me that this striking reptile is a 16-foot-[5 m] long female weighing some 180 pounds [80 kg]. Although her body is nearly as thick as a telephone pole, I learn that she is merely a “little leaguer” in comparison with the world record holder—a roly-poly female anaconda caught in 1960 that, it was estimated, weighed nearly 500 pounds [227 kg]!

No male anaconda can even dream of attaining to such dazzling dimensions. Although herpetologists knew that male anacondas are smaller than females, the field study found that males are so much smaller that they look like miniature versions of females. In fact, the study showed that females are, on an average, nearly five times bigger than males. That radical difference in size between the sexes can be misleading, as biologist Jesús Rivas discovered. He used to  keep a baby anaconda as a pet but always wondered why the little fellow kept biting him. Only during the field study did it dawn on him that he had been petting a full-grown and irritated male!

Wanted!—Reward Waiting

Although an anaconda’s bulk is its star quality, its length is equally impressive. Granted, anacondas are not as gargantuan as Hollywood depicts them—one movie featured a 40-foot-long [12 m] anaconda—but their maximum length of 30 feet [9 m] or so is breathtaking enough to contemplate.

Anacondas of that size are few and far between. The largest females caught during the study were 200-pounders [90 kg] measuring some 17 feet [5 m]. In fact, larger anacondas are so hard to find that a reward of $1,000, offered some 90 years ago by the New York Zoological Society (the forerunner of WCS), for any live snake over 30 feet [9.2 m] long has gone uncollected until this day. “We get two or three calls a year from people in South America who claim the reward,” says Mr. Holmstrom, “but when we ask them to send us proof of their catch in order to justify our going down there to check it out, the evidence never arrives.” Oh, by the way, the reward for a 30-footer [9.2 m] now stands at $50,000!

Close Up

I follow my guide as he leads me to the second floor of the reptile house, which serves as a holding and breeding area. The place is hot and humid. To give me an unobstructed look at my subject of interest, Mr. Holmstrom opens the door of an enclosure that holds a hefty female anaconda.

At this point, there are some eight feet [2 m]—and nothing else—between us and the animal. Then, the anaconda’s head rises slowly and moves steadily in our direction. By now only a distance of three feet [1 m] remains between the anaconda’s head and ours.

“We’d better back off,” says Mr. Holmstrom matter-of-factly, “she may be looking for food.” I readily agree. He shuts the door of the enclosure, and the anaconda’s head moves back until it gradually comes to rest near the center of its coiled body.

If you manage to ignore the anaconda’s malevolent-looking glare and take a good look at its red-striped head, you will see that it has remarkable features. The anaconda’s eyes and nostrils, for instance, form the highest points on its head. This allows the snake to submerge its body and head and leave its eyes and nostrils just above the water surface—much the way alligators do. That explains how the snake approaches prey while remaining camouflaged.

Tight Coils and Loose Jaws

The anaconda is not poisonous. It kills by wrapping its coils tightly around its prey. It does not crush its prey, but each time the victim exhales, the snake tightens its coils until the helpless victim suffocates. Almost anything—from ducks to deer—is considered fair game. However, reliable reports of people being eaten by anacondas are rare.

Since snakes cannot chew or tear their food, the anaconda has no choice but to swallow its dead prey whole—even if the prey is considerably bulkier than the snake  itself. In fact, if you could tackle food the way an anaconda does, you could wrap your lips around a coconut and gulp it down whole as easily as if it were a peanut. How does the anaconda do it?

“It walks its head over the prey,” says Mr. Holmstrom. He explains that the anaconda’s jaws are loosely attached to its head. Before setting its teeth into a bulky victim, its lower jaw can drop down and spread out. Then the anaconda pushes one side of its lower jaw forward, hooks its backward-facing teeth into the prey, and pulls that side of the jaw and the prey back into its mouth. Next, it repeats the same steps with the other half of its lower jaw. To some extent the upper jaw can do the same. With this alternating forward movement, the animal’s jaw seems indeed to be walking over the prey. Once the prey has been swallowed, which may take several hours, the snake yawns a few times, and the various parts of its flexible head fall back into place.

What prevents the anaconda from choking? The presence of an extendable windpipe located in the floor of its mouth. While working its food inward, the anaconda pushes its windpipe outward to the front of its mouth. That way, the snorkellike windpipe gives the anaconda access to air while eating.

Who Is Who?

My guide now removes the lid from a terrarium, and we look down at two young anacondas. Their identical looks make me wonder how the researchers could tell the difference between the hundreds of wild anacondas they studied during their Venezuelan project.

Mr. Holmstrom explains that they tried to solve the identification problem by making tiny branding irons out of paper clips. They heated the “irons” and branded small numbers on the anacondas’ heads. The method worked well until the snakes shed their skin—and their numbers! The researchers noticed, though, that each anaconda already carries its own identification mark. Each snake has a pattern of black blotches on the yellow underside of its tail—as unique to each snake as a fingerprint is to a human. “All we needed to do was to diagram the pattern found on a stretch of skin 15 scales in length, and we had enough variations to tell apart the 800 snakes that we studied.”

The Fastest, the Fittest, or the Strongest?

As we wrap up the interview in Mr. Holm-strom’s office, he shows me a picture he took in Venezuela of male anacondas all coiled around one another. It is a spellbinding sight. He explains that this knot of tangled anaconda bodies forms a so-called breeding ball. (See photo on page 26.) “Somewhere inside this ball is a female anaconda. One time we found a female with 13 males coiled around her—that was a record.”

Are the males fighting? Well, it’s more like a slow-motion wrestling match. Each of the male contenders tries to squeeze the others out and maneuver himself into a mating position with the female. The match may last for as long as two to four weeks. Who wins? The fastest (the male that finds the female first), the fittest (the male that produces the most sperm), or the strongest (the male that outwrestles the competition)? Researchers hope to find the answer soon.

At the end of the afternoon, I thank my guide for his captivating tour. As I travel back to my office, I reflect on what I’ve learned. Granted, I still don’t share the sentiments of biologist Jesús Rivas, that “anacondas are fun,” but I admit that anacondas definitely grabbed my attention. As researchers continue to trail anacondas in the wild, it will be interesting to learn whether these giant snakes will be inclined to shed more of their fascinating secrets.


^ par. 4 The Venezuelan Wildlife Department and parties to the Convention on International Trade in Endangered Species of Wild Flora and Fauna helped to fund the study.

^ par. 11 Journal of Herpetology, published by the Society for the Study of Amphibians and Reptiles, No. 4, 1997, pages 607-9.

[Picture on page 24]

The anaconda field study in Venezuela

[Picture on page 25]

William Holmstrom

[Picture on page 26]

An anaconda breeding ball