Pythons are nonvenomous constricting snakes in the family Boidae that are found only in the Old World. Like the boas, pythons retain lizard-like features such as paired lungs and the remnants of the hind limbs. Pythons are egg-laying snakes which distinguishes them from boas and sandboas which typically bear live young. Fossil species of pythons are known from Cretaceous period, some 200 million years ago, the separation of the old world pythons from the South American boas having taken place some 80 million years ago.
Constricting snakes do not crush their prey as commonly supposed, but coil tightly around the chest of the prey animal. When the animal exhales, the snake tightens its grip, and after two or three breaths the animal dies from suffocation or from the pressure on its heart which causes it to stop beating.
The large pythons in Australia and New Guinea include species of Liasis and Morelia which commonly exceed 10 ft (3 m) in length. The largest python in this region is the amethystine python (Morelia amethistina), which often exceeds 11 ft (3.5 m) but can grow up to 28 ft (8.5 m).
Australia also has the smallest pythons. Some species in the genus Liasis seldom exceed a yard (1 m) in length and have a slender body. The green tree python (Chondropython viridis) of New Guinea and northern Australia attains a length of about 7 ft (2 m), and has well-developed labial pits on the scales around the
mouth which serve as heat receptors, allowing the snake to locate warm-blooded birds and mammals at night.
The largest known python is the Asian reticulated python (Python reticulatus) which has been reported to attain a length of 38 ft (11.6 m), and commonly reaches more than 25 ft (7.6 m). Reticulated pythons are longest of all snakes, while the anaconda (an aquatic boa of tropical America) is probably the heaviest.
All pythons coil around their clutch of eggs to protect them, but the female Asian rock python (Python mdurus) incubates its eggs on cool nights by violently contracting her muscles several times a minute thus producing body heat. The female Asian rock pythons does not eat during the entire 60-90 day incubation period, and may lose almost half her normal weight due to this activity. Most Asian rock pythons have a gentle non-aggressive nature, and are a favorite of snake-handlers.
The Malayan blood python (Python curtus) is an (8-ft; 2.7-m) heavy-bodied snake, so named because of the blood-red color of some individuals, not because it sucks blood. Because of its size and bright coloration, blood pythons are popular pets.
The African rock python (Python sebae) grows to a length of more than 20 ft (6 m) and is able to eat animals as large as pigs and small antelope. Rock pythons have even been reported to (rarely) eat children. A large individual may take a food animal that weighs up to perhaps 100 lb (50 kg). The royal or ball python (Python regius) and the Angola python (Python anchietae) rarely exceed five ft (1.5 m) in length. The ball python gets its name from its habit of curling up into a tight ball with its head in the center; in this position the python can be rolled along the ground like a ball.
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Herndon G. Dowling