Alpacas usually live 15-20 years, stand 3½ feet at the shoulder and 4 feet at the head. The average weight of an adult is 150-180 lbs. Alpacas have feet with 2 soft pads, each with a stout toenail. Their padded feet make them very gentle on the land. Although technically not ruminants, alpacas do have multiple stomachs and they do chew their cud. They are herd animals and usually do not do well without at least one companion. Alpacas do spit at one another to show dominance, but humans are rarely targets of this behavior. Other forms of communication include quiet vocalizations and body posture.

Female alpacas are induced ovulators and do not have an estrous cycle. At sexual maturity, 1 to 2 years for females and 2½ to 3 years for males, mating will stimulate ovulation in a female if she is not pregnant. The gestation period for alpacas is about 11 months, and very rarely results in viable twin offspring. Babies, which weigh 15-20 pounds at birth, are called cria and are usually delivered without assistance.