Meet Marvin, the Pueblo Zoo's big, blissful bullsnake

June 3, 2018


Photo: Pueblo Chieftain


It is not unusual to see Marvin, the Pueblo Zoo bullsnake, "cuddling" with his box tortoise roommates, Tillie & Sunset. This sometimes alarms visitors, as they recall stories of snakes squeezing their prey to death; however, there is nothing to be alarmed about in this case.


Bullsnakes are carnivores, but he knows instinctively that he would not be able to digest the tortoises' upper shell (carapace). Also, bullsnakes do not squeeze their prey to death.


Like several other exhibits at the Pueblo Zoo, theirs is a multi-species habitat. When possible, zoos will try to mimic animals' natural habitats by combining different species that might be found in the same area in the wild.


Why do they make suitable roommates? Bullsnakes and tortoises have different diets, so they don't compete for food. Both species are coldblooded, so they have similar temperature requirements. For example, they need an external heat source, such as a heat lamp or heated water, to warm up.


This may explain why at times Marvin may coil around a warm tortoises' shell that just recently emerged from under a heat lamp.


Bullsnakes, like all snakes, shed so their skin can accommodate growth and to refresh the health of their outer covering. They generally shed once a month.


Just prior to shedding, their eyes turn a blueish color, which is referred to as being "in the blue." Snakes don't have eyelids, so this blue fluid covers the eye as it sheds the protective eye cap.


Just prior to shed, their color is dull and their belly turns pinkish. Their new skin looks much more vibrant. Shedding takes a couple of days, and they don't eat during that time so they usually try to eat a larger meal before starting the process.


They will soak beforehand to help the skin in peeling off. That is why visitors may see Marvin coiled up in water.


Marvin came to the zoo when he was 1 year old, in 2007. At that time he was the size of a new pencil. He is now 5 1/2 feet long. A snake's growth depends on its environment and how much it can get to eat. Of course, the snake is fed healthy, regular meals at the zoo, so his growth has been very good.


Just The Facts

Scientific name: Pituophis catenifer sayi

Common name: Bullsnake, also called Gopher Snake in different parts of the country

Description: The Bullsnake's scientific name "catenifer" means chain (catena) carrying (ifera) and is a reference to the snake's markings. The body is yellowish-tan with dark-brown to black blotches that alternate with two rows of dark spots on each side, somewhat resembling a chain. The tail, which is longer in males than in females, ends with eight to 15 dark stripes. Their ventral side is pale yellow or white, sometimes spotted.


Distinguishing features on the face are a single scale on the snout that is raised above the rest, and a dark band that crosses the head in front of the eyes.


Bullsnakes are large, stout snakes that can grow to 6 feet long or more, although the average is about 5 feet. Pituophis catenifer sayi is named for the American naturalist Thomas Say.


Range: Bullsnakes are found from Canada to Mexico in a wide band that includes southern Alberta and Saskatchewan, the Western and Midwestern U.S. and Mexico as far south as Tamaulipas.


Habitat: Bullsnakes inhabit a variety of ecosystems from desert to forest. They can live in prairies, shrublands, coniferous forests, farmland and even marshes. They can be found moving along the ground, underground and in the trees.


Behavior: Rodents such as mice, rats and gophers, ground nesting birds and their eggs, small reptiles and insects make up the diet of the bullsnake. Usually they are diurnal, but may be active at night during the heat of summer.


They are able to dig their own burrows with their pointed snouts, but often use the abandoned homes of other ground dwelling animals. They may spend up to 90 percent of their time resting in their underground homes. Bullsnakes go through periods of dormancy during the winter when they eat very little food.


When they are threatened, bullsnakes are able to vibrate their tail in a good imitation of a rattlesnake, which they resemble physically. They also can make a hissing sound with a membrane in the glottis. However, bullsnakes are not venomous or aggressive and provide a great service to humans by keeping rodent populations under control.


Reproduction and rearing: Bullsnakes mate in the spring between March and May. Females are sexually mature after two seasons and males mature earlier, at about 1 1/2 years old. The females lay anywhere from three to 24 eggs in a burrow or in cavities found in tree roots or piles of rocks. Sometimes females use communal nests.


The eggs hatch in late summer, after 64 to 80 days of incubation. The hatchlings are about a foot long and grow quickly, eating bugs, young mice and small lizards. The hatchlings fend for themselves and do not receive any parental care.


Under good conditions, a female can have two clutches in a season. Male and female bullsnakes live solitary lives and only get together for mating.


Predators: Large birds of prey, such as hawks and eagles, as well as foxes and coyotes, will eat bullsnakes. Juveniles are also eaten by other snakes. Road mortality represents another hazard for bullsnakes, as they like to bask in the heat of the asphalt surface.


Lifespan: In captivity, bullsnakes can live for 20 to 25 years on average, with one specimen living as long as 33 years. They live for 12 to 15 years in the wild.


Conservation Status: The IUCN Redlist lists bullsnakes as a species of Least Concern due to its large and stable population numbers.



-- Anne Casey

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