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Boa constrictor

Class: Reptilia
Order: Squamata
Family: Boidae
Genus and Species: Boa constrictor
  • A large snake with a black and white diamond pattern rests on a log near fallen leaves and dirt
  • A close-up of a large snake with a black and white diamond pattern rests its head on part of its body
  • A close-up of a large snake with a black and white diamond pattern rests on a log near fallen leaves, dirt and a large rock
  • A large snake with a black and white diamond pattern rests on a log near fallen leaves, dirt and a large rock
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Boa constrictors are nonvenomous snakes found in Central and South America. They are named after their mode of predation: constriction.
Physical Description

While many others may be afraid of boa constrictors, there are very few cases of them attacking humans; even human babies are too large to be suitable prey for boa constrictors. In fact, in some places in South America, boa constrictors are used to control rat infestations inside homes.

Depending on the habitat that a boa constrictor occupies, its patterns and coloring vary to allow it to camouflage. The body can be tan, green, red, or yellow and will have cryptic patterns that form bars, jagged lines, diamonds, and circles.

Their teeth are small and hooked, which allows for a strong grip when the snake strikes its prey and prevents the prey from wiggling free while the snake wraps its powerful body around the victim. It is commonly believed that boa constrictors subdue their prey by crushing their bones or squeezing their lungs to suffocate them, but recent research on the constriction method revealed that these snakes employ a different strategy all together.

Once the snake has its body wrapped around the prey, it squeezes just enough to cause a “circulatory arrest” by cutting off the ability of the heart to pump blood in and out. By keeping blood from flowing to the brain, the animal dies.

Larger members of the Boidae family have heat-sensitive pits on their heads, but boa constrictors do not. Instead, this animal relies on its tongue and its excellent vision to collect sensory information about its surroundings (like other snakes do). 

Size

They range in length from 20 inches (50 centimeters) as newborns, or neonates, to 13 feet (3.9 meters) as adults. They can weigh more than 100 pounds (45 kilograms) when full grown. 

Native Habitat

Boa constrictors are found from northern Mexico to Argentina. Of all the boas, constrictors can live in the greatest variety of habitats ranging from sea level to moderate elevation, including deserts, wet tropical forests, open savannas and cultivated fields. They are both terrestrial and arboreal.

Like its cousin, the green anaconda, the boa constrictor has impressive swimming abilities. However, unlike other snakes, it shows little inclination toward swimming in water. Instead, boa constrictors prefer to stay on dry land, either inside of hollow logs or abandoned animal burrows.

Food/Eating Habits

The boa constrictor is named for its mode of predation: constriction. Instead of injecting poison into its prey, it strikes, grabs and squeezes until the prey is subdued. Once the prey is dead, the snake swallows it whole.

Boa constrictors are able to adjust their hunting behaviors according to the density of possible prey items in their habitat. In most cases, they are ambush predators, meaning they sit and wait for a desirable prey item to pass by. However, if food is scarce, they become more active to seek out prey.

They feed on large lizards, small or moderate sized birds, opossums, bats, mongooses, rats and squirrels. At the Smithsonian's National Zoo, they eat mice, rats and chicks.

Social Structure
They are largely solitary animals until the breeding season.
Reproduction and Development

Litter size: 10-64 young, average of 25

Gestation: 5-8 months

Boa constrictors live in areas that are generally subject to wet and dry seasons. Once seasonal rains have subsided and give way to the dry season, male boa constrictors embark on the task of seeking out a mate. Males breed every year, but females may not. Females are also widely dispersed.

Females take one or more mates during the breeding season. To help lure a male, the female emits a scent from the cloaca that signals she is ready to breed. The male fertilizes the eggs by joining with the female at the cloaca. Fertilization is internal, and the gestation period varies depending on the local temperature.

Females give birth to live, independent young. The young spend most of their time up in trees while they grow to be heavy and large, at which point they spend more time on the ground. Boa constrictors reach sexual maturity at 2 to 3 years old. 

Sleep Habits
As nocturnal animals, boa constrictors hunt at night.
Lifespan
Boa constrictors live 20-30 years in the wild.

Boa constrictors have not been assessed by the International Union for Conservation of Nature. They are listed under CITES Appendix II, and the subspecies B. c. occidentalis is listed on Appendix I.

They are hunted and collected for their skin, which is considered exotic in many parts of the world.

Humans and boa constrictors have a somewhat mutually beneficial relationship in many parts of tropical America, where they are valued pest controllers. Some homes even bring constrictors inside to prevent or quell rodent infestations. 

They are also common in the pet trade, though pet owners are often unaware of how quickly they grow from a small neonate to a large adult. While this snake's status in the wild has not been assessed to determine the impact of the pet trade on populations, many boa constrictors are imported into the U.S. to become pets. People also breed boa constrictors, often producing snakes with more vibrant colors than their wild counterparts.

While the pet trade may not necessarily be a threat to this animal, their trade can pose a threat to other animals. In many unfortunate cases, an owner will simply release a boa constrictor that has grown too large into a local park or open area. Because boa constrictors are habitat generalists with the ability to vary their choice of prey, they can do well in the places where they are introduced, as long as the temperature conditions allow for their survival. 

The introduction of boa constrictors and other large, nonnative snakes into southern Florida has had devastating consequences on habitats that are already under immense pressure due to human development, the dispersal of nonnative species and climate change. There are now breeding populations of boa constrictors across southern Florida that are predating at-risk species into extinction.

While nature centers and zoos will not take snakes from pet owners, some local agencies use innovative strategies to address the impacts of invasive species, such as the boa constrictor. For example, the Florida Fish and Wildlife Conservation Commission hosts a series of events called Exotic Pet Amnesty Days. On these dates, this state government group collects exotic pets that owners would like to surrender with no questions asked.

Help this Species
  • Choose your pets wisely, and do your research before bringing an animal home. Exotic animals don’t always make great pets. Many require special care and live for a long time. Tropical reptiles and small mammals are often traded internationally and may be victims of the illegal pet trade. Never release animals that have been kept as pets into the wild.
  • Share the story of this animal with others. Simply raising awareness about this species can contribute to its overall protection.
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