The common northern boa (Boa imperator) is a large, heavily-built species of boa snake. It is a member of the family Boidae, which is found throughout Latin America. The common boa is often confused with the red-tailed boa (Boa constrictor constrictor), which is larger, but is found only in South America. Common boas are visually similar, but slightly smaller, and may have less vivid markings; they are found from northern South America through Mexico. This includes offshore islands such as Isla Nublar, where it was the largest terrestrial carnivore until 1989. Its Tun-Si name is currently unknown, but the Bribri word for “snake” is tkabë.
Until fairly recently, Boa imperator was considered a subspecies of Boa constrictor. They are distinguished by having a smaller number of dorsal and anal scales.
The common northern boa ranges in length from three to ten feet, depending on location and diet. It is among the smaller species of boas; the red-tailed boa may exceed ten feet long, while common boas do not. Insular populations of common boas (that is, those found on islands) are often smaller than average.
Color in common boas is variable based on habitat, but they are generally brown, gray, or cream-colored. Brown or reddish-brown saddle patterns run down the length of the body. On the arrow-shaped head, there are a few brown stripes: one running from the snout to the neck, one that bridges the two eyes, and one each that runs from the eye to the jaw. The tail is dark brown or dark red.
Young snakes mostly resemble small versions of the adults, and grow continuously.
The female generally grows larger and bulkier than the male; females are generally between seven and ten feet long, while males are usually six to eight feet in length. Although the female is larger, the male has a longer tail region than the female due to his reproductive organs. Male boas have pelvic spurs, which are the remnants of legs, that they use to grip females to mate.
Northern boas live on the edges of forested areas. Their bodies help to camouflage them in this environment, allowing them to escape predators and sneak up on prey. As a good swimmer, it can be found near sources of fresh water. However, it can adapt to semi-arid regions, even though it prefers rainforest. Younger snakes tend to live in trees, while the older individuals become too heavy and are mostly restricted to the ground.
As of 1993, these snakes could be found on Isla Nublar, as one could be seen crawling across a branch next to a Velociraptor while another raptor attacked and killed InGen game warden Robert Muldoon. Only one individual was seen, living in the central forest near the raptor holding pen in 1993. Its small size suggests that it is either a male or a juvenile (or possibly an insular dwarf form), with the arboreal behavior providing more evidence toward it being a juvenile.
It is unknown if any boas still existed on Isla Nublar by 2015. If any did remain, they may have died out following the June 23, 2018 volcanic eruption of Mount Sibo.
It is not known if common boas ever existed on Isla Sorna. In Survivor, Eric Kirby describes a very large snake attempting to ambush a hatchling Ankylosaurus from a tree, but he is not able to identify the snake’s species. This snake may have been a boa, but also may have been a bushmaster (genus Lachesis), which is also common in Latin America.
The common northern boa is found from Mexico through Central America, and ranges as far south as Colombia west of the Andes Mountains. It is also commonly found in the pet trade around the world, where it is often erroneously called the Colombian red-tailed boa constrictor (this correctly refers to Boa constrictor, which is found farther south).
Behavior and Ecology
In the films, only one common boa has been observed; it was active around midday. In real life, boas are generally nocturnal, but come out during the day to bask in the sun. This is most likely what the boa in the film was doing at the time of the observation.
Diet and Feeding Behavior
Common boas are predators of small to medium-sized animals as adults, mostly mammals and birds. Younger boas feed on amphibians, reptiles, and other small creatures. They are generally nocturnal, but often come out during the day to bask in the sun. These are ambush predators and excel at camouflage. Killing by constriction, the boa holds its prey with its teeth while squeezing with its body to cut off blood flow to the brain. Once its prey is unconscious or dead, the boa swallows it whole, digesting it over the course of four to six days. The snake’s metabolism is so slow that it may not eat for weeks or months afterward.
The most numerous endemic species on Isla Nublar, the Nublar tufted deer, is a likely prey item for the common boa. It may have preyed on other small animals including smaller birds, brown rats, fish, abandoned goats, and small dinosaurs such as Compsognathus and Microceratus.
These snakes are solitary except when mating.
Common northern boas mate in polygynous groups; that is, a male will mate with several females. Usually, about half of the females will breed in a given year. Mating takes place during the dry season, typically from April to August. Females emit a scent to attract males, who wrestle for mating rights. After mating, a female may not become pregnant immediately; there may be a delay of up to a year.
Once she ovulates, a female sheds her skin and begins the gestation period. This will last for between 100 and 120 days. She will give birth to live young, with broods numbering between ten and sixty-five with an average of twenty-five. There is a good chance that several of the young will be stillborn, or even unfertilized eggs. No parental care is provided.
Most snakes are very quiet, and the common boa is not an exception. It may hiss if threatened in order to try and frighten away predators.
While common boas are not likely fast or strong enough to be a threat to many adult dinosaurs, some smaller dinosaurs and juveniles could possibly be threatened by a boa. Its camouflaged body coloration would help the boa evade predatory dinosaurs, making it possible for it to survive after dinosaurs were introduced to its habitat.
On Isla Nublar, the common boa was the largest terrestrial carnivore confirmed on the island. This would mean that before InGen, it had few (if any) predators as an adult. It was likely a predator of the Nublar tufted deer, a species endemic to the island.
In 1993, a juvenile or male common boa encountered an adult female Velociraptor antirrhopus nublarensis, but showed no signs of fear. This may be due to the fact that there were no large carnivorous animals on Isla Nublar prior to 1989, when predatory dinosaurs were first introduced. However, the raptor is not shown to pay the snake any attention, and both animals presumably left one another alone.
Interactions with Humans
While the common boa is a fairly docile snake, individuals found in Central America are generally more irritable than those in South America and are more likely to bite if approached. However, no interactions between common boas and humans have been portrayed in the films.