Taxonomy

The bullsnake is a member of the Pituophis genus, a group of nonvenomous snakes in the Colubridae family, comprising the snakes commonly known as gopher snakes and pine snakes (Uetz & Hallermann 2018). The genus is comprised of seven species and sixteen subspecies, ranging throughout North America from Canada to Mexico (Uetz & Hallerman 2018). Scientifically, the bullsnake is known as Pituophis catenifer sayi; it is a subspecies of the gopher snake. The etymological history of the genus name Pituophis comes from the Greek word pitys, meaning ‘pine,’ and ophis, meaning ‘serpent.’ The genus name catenifer is derived from Latin, with catena meaning ‘chain’ and ifera meaning ‘bearing’ (Illinois Natural History Survey 2018). The subspecies name sayi is a patronym in honor of Thomas Say, a well-known American naturalist and zoologist of the eighteenth/nineteenth century responsible for describing over one thousand beetles, four hundred insects, and seven snakes, and who is honored in not just the patronym of the bull snake, but also eleven other taxa. Pituophis catenifer was originally described by Henri Marie Ducrotay de Blainville in 1835, while the subspecies P. c. sayi was described two years later in 1837 by Hermann Schlegel (Illinois Natural History Survey 2018). 

Description

Bullsnakes are one of the largest native snakes in North America, dwarfed only by the eastern indigo snake, Drymarchon corais couperi (National Park Service 2015); this is dismissing the presence of the invasive Burmese pythons and green anacondas in the Florida everglades. The bullsnake can reach lengths of over seven feet, with individuals commonly ranging from fifty to seventy-two inches long (National Park Service 2015). They are also heavy bodied, with larger species capable of weighing almost ten pounds (Snake Facts). Its coloration is a yellow-tan with rectangular blotches on its dorsal side that can range in shades from brown to black to reddish, forming a slight checkered pattern; the tail has between nine to nineteen dark bands (Canadian Herpetological Society 2017). This coloration provides them perfect camouflage in their grassy habitats. The ventral side is a light cream-yellow with black checker marks (Illinois Natural History Survey 2018). The scales are strongly keeled, giving them a rough texture (Illinois Natural History Survey 2018). Its eyes are an orange or reddish color with round pupils (National Park Service 2015). The head is very distinct, being disproportionately small in comparison to the body, with black bars around the eyes and mouth, and a slightly elongated and upturned rostral scale (Kapfer 2007); this scale is not as distinct as those seen on species like the hognose snake, but it still functions to assist the snake in burrowing. Common to other snakes in the Pituophis genus, these snakes have a thin and flexible epiglottis that, when air from the trachea is forced through it, creates a loud hiss that has been described as similar to the grunt of a bull, likely giving the snake its common name (Schmidt & Davis 1941).  

Range and Habitat

As previously mentioned, this species is highly wide ranging, appearing from southern Canada to Northern Mexico and from California east into Indiana (Canadian Herpetological Society 2017). Instances of interbreeding in areas where multiple subspecies of P. catenifer interact on the boundaries of their ranges lead to some taxonomic confusion (National Park Service 2015). They can have extensive territory ranges, with a single snake capable of utilizing over a square mile of space for its daily activities (Carpenter Nature Center 2016), and they can travel even more than that distance to reach their summer habitat from their winter hibernacula (Canadian Herpetological Society 2017). As a native of the American Great Plains, the bull snake prefers habitats such as grasslands, sandhills, shrublands, prairies, and old agricultural fields (National Park Service 2015); in Illinois, they are extensive throughout the sand prairies in the central and northwestern counties (Illinois Natural History Survey 2018). They can spend up to sixty percent of their time in burrows underground, typically using old gopher burrows as a site to hunt and hide from predators (Carpenter Nature Center 2016). In order to avoid harsh winter conditions that occur throughout much of their range, bull snakes hibernate below the frost line in their underground burrows, typically in groups. It is interesting to note that these aggregations often are not just of conspecifics; bull snakes have been known to share hibernacula with racers, milksnakes, garter snakes, and even rattlesnakes (National Park Service 2015). Additionally, each species enters and leaves the hibernacula at different times – the bullsnake will leave in the spring after garter snakes but before rattlesnakes (Graham 1997). 

Diet

Bullsnakes commonly consume small mammals, particularly rodents, as well as the occasional bird and their eggs, and even newborns are capable of capturing and consuming small mice (Graham 1997). They will also consume frogs when available, but this makes up a very small portion of their diet (Wheaton Park District 2018). These large snakes are constrictors, subduing their prey via strangulation before consuming it whole (Graham 1997). As a diurnal species, they hunt for prey during the day, typically in the morning and late afternoon in order to avoid direct sunlight of midday but still benefit from the warmth of the environment, and when the temperatures in peak summer get too hot, they will occasionally switch to being active at night for several weeks (Graham 1997). During the day they will also alternatively bask or seek cooler shelter, a cycle that aids in digestion and energy conservation before and after hunting (Graham 1997). Mammals like skunks or birds of prey like raptors commonly predate on the young, but once they reach their full length, they have few predators and remain relatively undisturbed (Graham 1997).

Reproduction

Bullsnakes begin to mate once they emerge from their hibernacula in March through May, with males emerging earlier than females (Graham 1997). Males reach sexual maturity earlier in life, at one to two years old, but females mature later at three to five years (Canadian Herpetological Society 2017). The female will excavate burrows and lay a clutch of eggs in late summer, between June and August (National Park Service 2015). A single clutch typically has between three to twenty-four eggs, usually over two inches long and creamy white with the stereotypical parchment shell common to all snakes (Graham 1997).  What is interesting is that, much like their hibernacula, nesting sites also tend to be communal, so a particularly large clutch of eggs in a burrow is likely to be from more than one female (Illinois Natural History Survey 2018). The young are left unattended and hatch in August or September, an average of around eighty days, and are around twelve inches long (Illinois Natural History Survey 2018). They will disperse quickly from the nest because they need to find their own meals; as previously mentioned, even these relatively small young are capable of constricting small rodents (Graham 1997). In the wild, these snakes can live to be around twelve years old, and in captivity this more than doubles to around thirty years of age (Carpenter Nature Center 2016). This old age is possibly due to their adult size, as other animals do not easily consume them.

Temperament

  The bullsnake is a nonvenomous snake, and is generally nonaggressive as well, but due to its coloration and defense display, it is commonly mistaken for rattlesnakes, especially in the west where these two snakes’ ranges overlap the most. When threatened, the bullsnake will sound off its characteristic hiss, as well as vibrate its tail in the grass to produce a rattle-like sound, puff up their body, and rear up defensively (2017 Herpetological Society). They will strike and bite as a last resort. Despite this, bullsnakes are common in the pet trade and, with handling and proper care, are much more docile and less susceptible to striking. 

Ecological Role and Conservation Status

These snakes are highly common throughout their range, listed as a species of ‘Least Concern’ on the IUCN Red List (IUCN); however, in some states they are species of special concern due to the destruction and disappearance of their native habitat (Carpenter Nature Center 2016). They are also listed as a protected species in Wisconsin (Kapfer 2007). As they are pushed out of their natural habitat with greater frequency, these adaptable snakes will find adjusted residency in agricultural and suburban areas, taking refuge in barns or under porches (Graham 1997). Their presence in these areas is actually highly beneficial, as they are excellent at controlling populations of rodents that could otherwise decimate crops or become a home invasion pest; because of this, educated land owners tolerate the bullsnake’s presence and understand that they serve as a positive. However, due to their large size and their similarity in appearance and behavior when disturbed to rattlesnakes, they are often killed out of fear and misunderstanding. This is unfortunate not only because it impacts the bullsnake population, but because they are key predators in their food web, it leaves space where the system remains unchecked, impacting the trophic level populations both above and below it.  A strange rumor also exists that claims the bullsnake is capable of breeding with a rattlesnake and creating venomous offspring – as they are two distinct species, they cannot interbreed, so this should not be a realistic fear (National Park Service 2015). 

Ethogram

I observed the behaviors of the captive P. c. sayi at the Wildlife Discovery Center in Lake Forest, IL, on November 12th and December 3rd, 2018 for 110 minutes and 75 minutes, respectively. This snake was in an enclosure with an appropriate sized hide (half a log), water bowl, two plants, and a large rock, as well as lights and heat lamps that were controlled by a timer. The complete ethogram is attached in the Appendix, broken down by one-minute intervals for both days. Below is the table of all behaviors displayed by the snake throughout the observation period.

The snake was much more active on the first day of observation than the second; it only spent 41 out of a total 110 minutes resting (37%), while on the second day it spent 62 out of 75 minutes resting (83%). It only burrowed, body dug, and climbed on the first day, but the second day was the only time that it foraged and fed; it is important to note that this was the only day food was presented to it during the study, otherwise this behavior may have been seen on the first day as well. 

The behaviors observed coincide clearly with behaviors that can be seen in the bullsnake’s natural setting. Particularly on the first day, the snake spent a large period of time digging and burrowing (36% of the time), which is a behavior that the snake is built to do, with its distinctly shaped head and rostral scale. As there are no burrows occurring in the enclosure at the Wildlife Discovery Center, it makes sense that the snake would create these burrows itself, and it may be doing so to mitigate its body temperature or otherwise simulate its natural activities. The snake also climbed up the wall several times on the first day of observation; while they are not arboreal, bullsnakes are apt climbers over rocks and other obstructions in their native prairies and scrublands, so this is an expected behavior. The increased time spent resting on the second day is not particularly unusual, though it does contrast sharply with the highly active first day. Despite being a diurnal snake, they still spend significant time basking throughout the day, especially if they recently had a meal (though this snake’s feeding schedule was not known at the time). It is likely that the snake may be decreasing activity, as it is relatively late in the year. Even snakes in captivity that are kept at consistent temperatures year round will decrease activity to mimic their natural periods of dormancy. As this second session took place in early December, this is not an impossible conclusion to reach to explain the sharp decline in activity. With more periods of observation, this trend may have been able to be marked more closely and demonstrate possible dormancy behaviors. 

While highly preliminary and lacking definitiveness, the results of my observations are interesting and can provide suggestions for their continued care in captivity at zoos, rehabilitation centers, and wildlife facilities. These snakes are natural burrowers and can be highly active throughout the day. It is essential that the enclosure they are kept in contains enough substrate of the proper consistency to allow them to create burrows, both for thermoregulatory purposes, but also to prevent ‘boredom’ that may make them temperamental or aggressive. If space provides, it could be interesting to provide captive bullsnakes with enclosures containing premade burrows that allow them greater exploration of their space. It is important not to neglect their climbing abilities as well; because of their natural tendencies, they are capable of climbing up the walls of their enclosure. This is necessary to consider from the safety aspect, as open tops or holes in the ceiling of the enclosure could be easily accessed by bullsnakes compared to other snakes that are smaller or not as strong of climbers. This snake was also observed using some of the lighting wiring to climb and even rest on, so if a heat lamp is installed on the ceiling where a snake could climb to, they could easily overheat or burn themselves, so proper preventative measures should be taken. However, this climbing ability can also be utilized for habitat stimulation, as caretakers could put in stacks of rocks or other structures that provide the snake places to climb, as well as additional hide areas. 

Watching the snake forage through scent tracking and feed on the mouse that was added near the end of the second day provides an excellent basis on the possibility of enrichment activities for the snake. Caretakers can consider breaking up large feedings by giving the snake several smaller meals, like young mice, hidden around the enclosure. As captive snakes are often fed already dead prey items, this would increase the activity required of the snake, which can keep it healthier and in better temperament. Even if the caretakers do not wish to change feeding schedules, the addition of mouse scent throughout the enclosure would be a simple way to engage in the bullsnake’s natural active foraging behavior and provide opportunity for greater activity. 

These suggestions are based on preliminary observations, but the behaviors seen in a captive bullsnake closely match the expected behavior of a wild individual, and the more an institution can cater to the needs of the species in their collection, the better we can continue to admire, observe, and care for Illinois’ largest snake.

Appendix

DAY 1

DAY 2