The Rubber Boa ( Charina bottae) is a fascinating, non-venomous snake species belonging to the Boidae family. Its common name comes from its unique skin, which is loose, wrinkled, and composed of smooth, shiny scales, giving it a rubber-like appearance and texture. These docile snakes, found throughout the western United States and southern British Columbia, Canada, exhibit specific dietary preferences and feeding behaviors that are crucial to their survival.
Appearance and Distribution
Rubber boas typically range in color from tan to dark brown, with a lighter ventral surface, although some individuals may exhibit olive-green, yellow, or orange hues. Newborns often have a pink and slightly transparent appearance, which darkens as they mature. These snakes possess small eyes with vertically elliptical pupils and short, blunt heads that are no wider than their bodies. One of their most distinguishing features is their short, blunt tail, which closely resembles the shape of their head.
The distribution of rubber boas spans a significant portion of western North America, from the Pacific Coast eastward to western Utah and Montana, extending south to the San Bernardino and San Jacinto Mountains in California, and north to southern British Columbia. They have also been sighted in Colorado and Alberta.
Habitat and Behavior
Rubber boas are adaptable snakes that inhabit a wide variety of habitats, including grasslands, meadows, chaparral, deciduous and conifer forests, and high alpine settings. They are primarily nocturnal and crepuscular, spending much of their time under shelter such as rocks, logs, leaf litter, and burrows. These snakes are good climbers, burrowers, and swimmers, and they tend to maintain relatively small home ranges.
Dietary Preferences
Rubber boas are carnivores with a diet primarily consisting of young mammals such as shrews, voles, and mice. They are particularly effective at locating and consuming nests of young rodents. While their natural diet mainly includes nestling rodents, they will also consume native lizards and their eggs. In captivity, a diet of mice is suitable for their entire lifespan.
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Hunting and Feeding Behavior
Most foraging occurs at night, with the rubber boa constricting its prey to kill it. They are known for their patient approach to eating, often taking their time to thoroughly smell the prey before gently starting to consume it. Unlike many other snakes, rubber boas rarely strike to capture their prey and tend to avoid fast-moving targets.
One interesting behavior observed in laboratory feeding trials involves the use of their tail as a predatory defense. The boa will prey on nestling mice while using "false strikes" of its tail to keep the mother mouse at bay. The adult mouse focuses its attention on attacking the tail, allowing the boa to consume the nestlings.
Captive Feeding Considerations
In captivity, feeding rubber boas can sometimes be challenging. It is theorized that lab mice ( Mus musculus) may not smell like food to them. Young or newly wild-caught boas often readily consume deer mice (Peromyscus), voles (Ellobius), and lizards (primarily Sceloporus), but may refuse lab mice. To entice them to eat lab mice, scenting, braining, or washing the mice may be necessary.
Baby rubber boas are born late in the summer or early fall, and it appears normal for newborns to overwinter where they were born, without taking a meal until late the next spring or early summer. Some newborns may refuse to eat during their first spring and summer, only consuming their first meal after 18 to 20 months.
Adult male rubber boas often refuse to eat until late spring or early summer, after the breeding season. Some males may only feed during June, July, and the first part of August, while others continue eating until September, fasting for the remaining months of the year.
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Reproduction and Life Cycle
Rubber boas mate shortly after emerging from hibernation in the spring, and young are born between August and November. They are viviparous, giving birth to live young, with up to 9 offspring per year, although many females only reproduce every four years. The gestation period lasts around 5 months, during which time females are often seen basking in the sun. Newborns are well-developed and typically 19-23 cm (7.5-9.1 in) long.
Conservation Status
According to the IUCN, the Rubber Boa is locally common and widespread throughout its range, although no overall population estimate is available. However, there is little research addressing the conservation status or impacts of anthropogenic disturbances on Rubber Boas. Potential threats include roadway mortality, habitat alteration, human-caused mortality, and chemical contamination.
Adaptations to Temperature
Rubber boas originate from climates with cold winters and have a strong tendency to brumate over the winter. They can tolerate cold conditions, with some observations of them sunning themselves in temperatures just above freezing. In captivity, brumation temperatures do not need to be extreme, even if the snakes can withstand temperatures at or just below freezing.
Rubber boas do not tolerate high temperatures, and a body temperature in the low 90s Fahrenheit can be fatal to them. The warm end of a rubber boa enclosure should not exceed 85 degrees Fahrenheit, while the cool end can be as low as 65 degrees during the active season.
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