Python vs Boa: What Is the Difference Between These Snakes?

Key differences at a glance

Pythons and boas look so alike that for a long time they were placed in the same family. Both are heavy-bodied constrictors with small spurs beside the vent, the last traces of hind legs. Both kill by squeezing, and both include giants. Today, scientists put them in two separate families: Pythonidae for pythons and Boidae for boas.

Their resemblance is partly because both groups have kept many features of early snakes, such as the remains of a pelvis and two lungs instead of one. DNA studies show that pythons are actually more closely related to the small sunbeam snakes of Asia and the Mexican burrowing python than to boas.

If you see a large constrictor in the wild, its location is usually the quickest clue. A big constrictor in Brazil is almost certainly a boa or an anaconda, while one in India, Thailand or Australia is a python.

Eggs or live young?

This is the clearest biological difference. All pythons lay eggs. A female python lays a clutch of leathery eggs and, in most species, coils around them until they hatch. Female Burmese pythons and a few other species even shiver to warm the clutch, a rare behavior in reptiles.

Boas, with very few exceptions, give birth to live young. The eggs stay inside the female, and the young are born fully formed, each wrapped in a thin membrane that it breaks soon after birth. A boa constrictor typically gives birth to a few dozen babies after carrying them for several months. The handful of egg-laying exceptions include the Calabar boa of West and Central Africa and the Arabian sand boa.

Read more about why some snakes lay eggs and others give birth in do all snakes lay eggs?.

Where pythons and boas live

The old rule says pythons live in the Old World and boas in the New World. It is a good start but not the whole story.

Pythons are native to sub-Saharan Africa, South and Southeast Asia, southern China, the Philippines, New Guinea and Australia. About 40 species are recognized, from the African rock python and the Burmese python to the small children’s python and anthill python of Australia. No true python is native to the Americas or Europe, although the Burmese python is now invasive in Florida.

Boas are most diverse in the Americas, from Mexico through Central America and the Caribbean to Argentina. This group includes the boa constrictor, the tree boas and rainbow boas, and the anacondas. Other boas live in Madagascar, on Pacific islands from New Guinea to Samoa, and in drier parts of Africa, the Middle East and Asia, where small burrowing sand boas live. One sand boa, the javelin sand boa, even reaches southeastern Europe. The United States has two native boas, the rubber boa and the rosy boa, both small, gentle snakes of the West.

Where the two groups do overlap, they tend to use different habitats.

Skull and teeth differences

Biologists separate pythons from boas with a few details of the head that you will not see on a live snake, but that are reliable:

• Front teeth. Pythons have teeth on the premaxilla, the small bone at the very front of the upper jaw. Boas have no teeth there. The only exception among pythons is the adults of the Australian genus Aspidites, which includes the black-headed python and the woma.
• The bone above the eye. Pythons have an extra bone over the eye socket, called the postfrontal or supraorbital bone. Boas lack it.

Both groups have many sharp, backward-curving teeth for gripping prey, and neither has fangs or venom.

Heat pits: how they “see” warmth

Many pythons and boas can detect the body heat of birds and mammals using sensitive pits along the lips. The position of these pits differs. In pythons, the pits sit within the scales of the lips. In boas that have them, such as tree boas and rainbow boas, the pits lie between the scales.

Many boas, including the boa constrictor itself, have no visible pits at all, though they still have heat-sensitive cells in their lips. The heat pits of pythons and boas evolved separately from the larger and more sensitive pit organs of rattlesnakes and other pit vipers, described in how do pit vipers sense heat?.

Which is bigger?

Both families include giants, but they win in different ways:

Most members of both families are much smaller. Many sand boas and the rubber boa stay under 80 cm (31 in), and Australia’s anthill python, among the smallest pythons, grows to only about 60 cm (24 in). For a ranking of the giants, see our list of the largest snakes, and for the two biggest head to head, see anaconda vs python.

Which is more dangerous?

Neither group is venomous, and attacks on people are rare. Most boas and pythons are too small to harm an adult. The danger comes only from the few giant species. The reticulated python is the only one with several well-documented cases of killing and swallowing people in the wild, in Indonesia. Large Burmese pythons, African rock pythons and anacondas are capable of killing a person, but such cases are extremely rare. A bite from a medium-sized boa can be painful but is rarely serious.

Can pythons and boas interbreed?

No cross between a python and a boa has ever been reliably documented. The two families split tens of millions of years ago and are far less closely related than their similar looks suggest. Closely related species within a family can sometimes hybridize, however. For example, Florida’s invasive Burmese pythons include individuals carrying genes from the Indian python.

How to remember the difference

A simple rule of thumb: pythons lay eggs and live in the Old World; boas give birth and live mainly in the New World. Anacondas are boas. Sand boas are boas, even in Africa and Asia. And despite the name, the Mexican burrowing python is neither a true python nor a boa, but a relative of both in its own family.