|Subspecies:||P. c. sayi|
|Pituophis catenifer sayi
Bullsnakes average about 6 feet (1.8 m) in total length, and specimens of up to 8 feet 4 inches (2.5 m) have been recorded. Adult specimens have been weighed from 1–3.6 kg (2.2–7.9 lb), though the heaviest known specimens can attain 4.5 kg (9.9 lb). This makes the bullsnake among the largest snakes native to Canada and the United States, although it is generally not as long as indigo snakes nor as heavy or as large in diameter as rattlesnakes. They are usually yellow in color, with brown, white, black or sometimes reddish colored blotching. The blotching pattern is as follows: large blotches on top, three sets of spots on the sides, and bands of black on the tail. Many color variations have been found, including albinos and white varieties. A scale count is required to distinguish juvenile bullsnakes from juvenile gopher snakes.
Bullsnakes eat small mammals, such as mice, rats, pocket gophers, ground squirrels, and rabbits, as well as ground nesting birds, birds' eggs and lizards. Juvenile bullsnakes depend on small lizards, frogs, and baby mice. Bullsnakes kill their prey via constriction.
The idea that bullsnakes occasionally eat rattlesnakes is sometimes given as a reason for humans not to harm bull snakes when encountering them in the wild, although a better reason is the bullsnake's role in controlling warm-blooded vermin such as rodents.
Though some bullsnakes can be docile, and with some time become accustomed to handling, most bullsnakes are quite defensive and known for their perceived "bad attitude".
When threatened by anything as large as a human, a bullsnake's primary defense is to rear up and make itself look as large as possible. It typically then begins lunging and retreating at the same time in order to escape.
Bullsnakes are sometimes mistaken for rattlesnakes and killed. Owing to its coloration, dorsal pattern, and semi-keeled scalation, the bullsnake superficially resembles the western diamondback rattler (Crotalus atrox), which is also common within the same range. The bullsnake capitalizes on this similarity by performing an impressive rattlesnake impression when threatened. First, it hisses, or forcibly exhales through a bisected glottis that flaps back and forth producing a convincing rattling sound. It also adopts a rattlesnake-like "S-curve" body posture as though about to strike. It will commonly vibrate its tail rapidly in brush or leaves, and flatten its head to resemble the characteristic triangular shape of the rattlesnake. These defensive behaviors are meant to scare away threats, however, and not to sound an attack.
In contrast to rattlesnakes, which usually keep their tail elevated in order to sound the most efficient rattle, bullsnakes tend to keep their tail in contact with the ground, where it can be vibrated against something.
Bullsnakes breed in March and usually lay their eggs in April or June. They lay on average a dozen eggs in sand or other protected areas and leave the eggs to incubate unprotected. Clutches of 5-22 eggs have been observed. The eggs are elliptical, leathery, rough, sticky, and up to 70 mm (2¾ in.) long. The eggs typically hatch in August or September. Baby bullsnakes are 20–46 cm (8-18 inches) at hatching. Their color is grayish until after their first shed.
- Conant, Roger, and Joseph T. Collins. 1998. A Field Guide to Reptiles and Amphibians of Eastern and Central United States. Third Edition, Expanded. Houghton Mifflin. Boston. 616 pp. ISBN 0-395-90452-8. (Pituophis melanoleucus sayi, p. 365.)
- Roots, Clive (2006). Hibernation. Greenwood Publishing Group. p. 89. ISBN 978-0-313-33544-0.
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- Ernst, Carl, and Evelyn Ernst. 2003. Snakes of the United States and Canada. Smithsonian Books. Washington, District of Columbia. ISBN 1588340198
- Schmidt, K.P., and D.D. Davis. 1941. Fieldbook of Snakes of the United States and Canada. G.P. Putnam's Sons. New York. 365 pp. (Pituophis sayi sayi, pp. 163-164 + Plate 18 + Figure 46. (map) on p. 161.)
- Conant, Roger. 1975. A Field Guide to Reptiles and Amphibians of Eastern and Central North America. Houghton Mifflin. Boston. 429 pp. ISBN 0-395-19977-8 (paperback). ("Genus Pituophis", p. 198.)
- Zim, H.S., and H.M. Smith. 1956. Reptiles and Amphibians: A Guide to Familiar American Species: A Golden Nature Guide. Simon and Schuster. New York. 160 pp. ("Bull Snakes", pp. 96-97.)
- Wright, A.H., and A.A. Wright. 1957. Handbook of Snakes of the United States and Canada. Comstock. Ithaca and London. 1,105 pp. (in 2 volumes) (Pituophis catenifer sayi, pp. 604-609, Figure 175. + Map 46. on p. 589.)
- Schlegel, H. 1837. Essai sur la physionomie des serpens, Volume II., Partie Descriptive. M.H. Schonekat. Amsterdam. 606 + xv pp. (Coluber sayi, pp. 157–158.)