6 interesting facts about boa constrictors

October 3, 2017, 8:34 a.m.
wild boa constrictor in Costa Rica
Photo: Tanguy de Saint-Cyr/Shutterstock

Boa constrictors are some of the most famous snakes on Earth. That's partly because they're popular as pets, but also because they're finely tuned wonders of nature — especially when they're living in the natural ecosystems where they evolved.

Here are a few things you may not know about boa constrictors:

1. All boas are constrictors, but there's only one boa constrictor.

"Boa" is a common name for more than 50 constricting snake species, all nonvenomous members of the family Boidae. It's also the name of a genus within that family, though, and the genus Boa contains only one recognized species: Boa constrictor. This is one of the fairly rare cases when a species' common and scientific names are the same, like Aloe vera or Tyrannosaurus rex.

Boa constrictors are New World snakes, native to habitats from northern Mexico through Central and South America. There are several distinct subspecies, including Boa constrictor constrictor (from the northern Amazon basin), B. c. amarali (from the southern Amazon basin), B. c. occidentalis (from Paraguay and Argentina) and B. c. nebulosa (from Dominica).

2. Boas give birth to live babies, which become independent within minutes.

Boa constrictors are "ovoviviparous," meaning their eggs stay inside the mother's body until they're ready to hatch, after which she gives birth to live young. Those baby boas hit the ground slithering, and are independent within minutes of their birth.

Most clutches include 20 to 50 babies, according to Seattle's Woodland Park Zoo, but the record is 77. Newborns are 17 to 20 inches (43 to 51 centimeters) long, and can grow up to 3 feet (0.9 meter) in several months. They reach sexual maturity at 3 or 4 years old, at which point some individuals may stretch more than 6 feet (1.8 m) long.

3. They don't kill their prey by suffocating it.

Boa constrictors are ambush hunters, often hanging from a tree until they can grab a passing animal with their jaws. Once that happens, they create two or more loops with their bodies to fully encircle their prey. By wrapping around the rib cage, they can compress their victim's vital organs and also monitor its heartbeat, letting them know when the deed is done.

But how exactly do they kill their prey? Scientists long thought boas kill with suffocation, squeezing an animal's rib cage so it can't refill its lungs with air. As a 2015 study found, however, they actually use an even quicker method: cutting off the blood supply.

Many animals can survive a relatively long time without air, as seen when humans are revived after nearly drowning. And because boa constrictors' natural prey can be dangerous — often equipped with sharp claws, teeth, hooves or beaks — the snakes need to work as quickly as possible. After a large meal, a boa constrictor may not need to eat again for weeks.

4. They still use what's left of their legs.

Like all snakes, boa constrictors evolved from four-legged ancestors. Boas are considered primitive snakes, though, because they still have some ancient features that have faded away in most snake species. That includes two functioning lungs (many snakes only use one lung, an adaptation to their elongated body shape) as well as remnants of legs known as "pelvic spurs."

Boas no longer need legs for locomotion, but they've still found uses for their vestigial limbs, which resemble a claw protruding from their underbelly. Males use them for mating, for example, and they reportedly come in handy during combat, too.

5. Living with boas is a long commitment.

Boa constrictors are naturally solitary snakes, and can adapt relatively well to captivity. "It is easy to obtain boa constrictors that have been captive-bred for generations, increasing their affinity for humans," according to the University of Michigan Museum of Zoology. "They are relatively undemanding pets, as long as their large adult size and space needs are accounted for."

That said, no human should enter such a relationship lightly. Wild boa constrictors can live for 20 to 30 years, and in the sheltered environment of a human home, they've been known to survive beyond 40 birthdays. That's a long-term commitment, and involves not just feeding and general care, but also maintaining a dry habitat to prevent health problems like scale rot.

"We do not recommend reptiles as pets for most people as they require very specialized diets and environments," the Woodland Park Zoo explains. "We also receive hundreds of requests each year to take former pet iguanas, boas and other reptiles but we cannot accept these due to space, health and unknown backgrounds." When exotic snakes escape or are released by their owners, they can cause big ecological problems. Boa constrictors rarely pose a direct threat to people, although large snakes should always be handled with extreme care — as a woman in Ohio was recently reminded — and fed with more than one person present.

6. In the wild, boas help control rodents and disease.

Boa constrictors are not an endangered species, but some wild populations have declined due to habitat loss, road mortality and overcollection for the pet trade, especially on offshore islands. And while wild snakes can seem frightening to some people, boa constrictors — like most snakes, and predators in general — provide valuable ecosystem services in their natural habitats.

Snakes famously eat mice, rats and other rodents, which often act as pests by raiding human food supplies and spreading disease. But boas' benefits may extend beyond rodents: In the American tropics, for example, native opossums can be carriers for the human disease leishmaniasis, which is transferred by blood-feeding sand flies that parasitize the opossums. By eating opossums, boas are believed to help regulate their populations, thus lowering the potential transmission of leishmaniasis to humans.

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