Like other boa species, the redtail boa continues to grow throughout its life. Size depends mainly on its age, but also on the food supply. When sexually mature, female redtail boas can reach 7 to 10 feet in length, while males are rarely longer than 8 feet. At birth, redtail boas are 15 to 20 inches long.
Redtail boas eat a variety of animals, from mice to big lizards. They ambush their prey, but can be active hunters in areas with low quantity of available prey. After grabbing the prey with their teeth, redtail boas coil around it, killing by constriction. Then, they swallow the whole prey. Digestion can take a week, depending on the prey's size.
According to their name, redtail boas show bright-red to reddish-brown "saddle" patterns on their tails. The anterior part of the body is often tan and yellowish to light-brown with dark brown to reddish saddle shapes. Rarely, a redtail boa with a white body and red patterns along its whole body is born in the wild, as the result of a genetic mutation that causes albinism.
Although the redtail boa constrictor is more common in the tropical rainforest of South America, it is also found in some semi-desert areas. The rainforest is an ideal environment for red tail boas, due to the high temperature and humidity, as well as the large quantity of prey. The species is a good swimmer, and is often found near rivers.