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Boas, pythons, and anacondas: What’s the difference?

Because boa constrictors, reticulated pythons, and anacondas are some of the biggest snakes in the world, many people get confused about which is which. The first thing to note is that the anaconda is a species of boa, not a separate type of snake. That leaves two groups, the boas and the pythons. These snakes have some things in common: they are constrictors, killing their prey by wrapping around it and suffocating it, and they are considered primitive snakes with two lungs (most snakes have only one) and remnants of hind legs and pelvic bones.

But they have differences, too. Pythons have one more bone in their head than boas do and some additional teeth, and pythons are found in the Old World (Africa, Asia, Australia) while boas live in both the Old World and the New World (North, Central, and South America). One of the biggest differences is that pythons lay eggs while boas give birth to live young, although some sand boas and the Round Island boa of Mauritius lay eggs.

Not the bad guys

Boas often appear in movies and stories that take place in the jungle, usually as the villain sliding menacingly through the trees. That’s probably because these big snakes make a big impression! But boas are usually pretty quiet and calm and don’t deserve their nasty reputation. They are not venomous, and many do not live in jungles.

Boa means "a large serpent” in Latin.
Female anacondas grow much larger than the males.
Boa constrictors like to eat bats! They catch them by hanging from tree branches or the mouth of caves and knocking the bats out of the air as they fly by.
When some boa species want to mate, several males coil around a female in a ball and wrestle with one another for up to two weeks before one wins—or the female makes a choice.
The rosy boa and the rubber boa are the only two boa species native to the US.
The largest snake ever was the titanic boa “Titanoboa cerrejonensis,” a type of boa that lived 58 million years ago. It was more than 40 feet (12 meters) long and weighed more than 1 ton (1 metric ton).
Many Madagascan tribes believe Madagascan tree boas are incarnations of their ancestors. In some villages, natives build special cages to house the snakes they believe are their parents or grandparents.
Big Ambergris Cay, a small island in the Caribbean, has one of the densest boa populations in the world. Only about 2.5 square miles (6.5 square kilometers), population estimates suggest there are over 2,000 boas on the island.
Boas and pythons have two vestigial limbs, which they can move but are not used to help them get around, that may be leftovers from the process of evolution.

Several boa species—Solomon Island boas, annulated boas, emerald tree boas, Madagascar tree boas, and green anacondas—can be seen in the San Diego Zoo’s popular Reptile House.

We also have boas that serve as animal ambassadors, visiting schools, hospitals, nursing homes, television studios, and classes and parties at the Zoo. When an education program needs a large, easily seen reptile at the San Diego Zoo, Manja is the man! He's a Madagascar ground boa. Born in 1996 at the Fort Worth Zoo in Texas, he came to the San Diego Zoo two months later and is named for a city in the part of Madagascar where these ground boas are found. He's nearly 20 pounds (9 kilograms) and over 6 feet (1.8 meters) long and so strong that he's usually brought out by two people to greet our visitors.

Manja is special for many reasons: he's only one of 32 Madagascar ground boas living in the US and the only one we know of who works as an ambassador! It's not often that people get to meet such a big snake and learn about one first hand, so he’s an ambassador for all snakes, helping teach people about the their important place in the web of life.

Two other boa ambassadors are Rosy, our rosy boa, who was born in 1962 and is still going strong, and Ruby, a red-tailed boa born in 2003.

The Turks and Caicos rainbow boa Epicrates chrysogaster is found only in the Turks and Caicos Islands and adjacent islands in the southern Bahamas of the Caribbean. Very little is published or known about this small, cryptic, constricting snake. It can reach 6 feet (1.8 meters) in length, but specimens this size are very rare, and the average adult size is slightly less than 3 feet (0.9 meters). Due to its small size, extremely docile temperament, and beautiful rainbow-like sheen, the species was heavily collected for the pet trade in the 1970s, raising concern for its survival in the wild.

Rainbow boa populations are now threatened by habitat destruction and introduced predators, including rats, cats, and dogs. A project began in 2009 to capture, measure, mark with PIT tags, and release the boas to document their daily and seasonal movements, habitat preferences, diet, reproduction, and sources of mortality. The information gathered can be used to make informed conservation and management recommendations for the islands where the species occurs.