Behavior
Alpacas are social herd animals that live in family groups consisting of a territorial alpha male, females and their young. They are gentle, inquisitive, intelligent and observant. As they are a prey animal, they are cautious and nervous if they feel threatened. They like having their own space and may not like an unfamiliar alpaca or human getting close, especially from behind. They warn the herd about intruders by making sharp, noisy inhalations that sound like a high pitch burro bray. The herd may attack smaller predators with their front feet, and can spit and kick. Due to the soft pads on their feet, the impact of a kick is not as dangerous as that of a hoofed animal, yet it still can give quite a bruise, and the pointed nails can inflict cuts.
Spitting
Not all alpacas spit, but all are capable of doing so. "Spit is somewhat euphemistic; occasionally the projectile contains only air and a little saliva but alpacas commonly bring up acidic stomach contents (generally a green grassy mix) and project it onto their chosen target. Spitting is mostly reserved for other alpacas, but an alpaca will occasionally spit at humans that, for example, take away food.
For alpacas, spitting results in what is called "sour mouth." Sour mouth is characterized by a loose-hanging lower lip and a gaping mouth. This is caused by the stomach acids and unpleasant taste of the contents as they pass out of the mouth.
Some alpacas will spit when looked at, others will never spit—their personalities are very individualized and there is no hard and fast rule in terms of social behavior, although there is often a group leader, and a group trailer/runt that is picked on by others.
Physical contact
Once they know their owners and feel confident around them, alpacas may allow their backs and necks to be touched. They do not like being grabbed. Once socialized well, some alpacas tolerate being stroked or petted anywhere on their bodies, although many do not like their feet, lower legs, and especially their abdomen touched or handled. If an owner needs to catch an alpaca, the neck offers a good handle—holding the neck firmly between the arms is the best way to restrain the animal. Holding the neck from the rear with the animal's head under one's arm is also very effective.
Hygiene
To help alpacas control their internal parasites they have a communal dung pile, where they do not graze. Generally, males have much tidier, and fewer dung piles than females who tend to stand in a line and all go at once. One female approaches the dung pile and begins to urinate and/or defecate, and the rest of the herd often follows.
Because of their preference for using a dung pile, some alpacas have been successfully house-trained.
Sounds
Individuals vary, but Alpacas generally make a humming sound. Hums are often comfort noises, letting the other alpacas know they are present and content. The humming can take on many inflections and meanings, from questioning to a high-pitched, almost desperate, squealing when a mother is separated from her offspring.
Alpacas make a variety of sounds. When they are in danger, they make a high-pitched, shrieking whine. Some breeds are known to make a "wark" noise when excited. Strange dogs—and even cats—can trigger this reaction. To signal friendly and/or submissive behavior, alpacas "cluck," or "click" a sound possibly generated by suction on the soft palate, or possibly in the nasal cavity. This is often accompanied by a flipping up of the tail over the back.
When males fight they also scream, a warbling bird-like cry, presumably intended to terrify the opponent. Fighting determines dominance, and therefore the right to mate the females in the herd, and it is triggered by testosterone. This is why males are often kept in separate paddocks—when two dominant males get together, violent fights often occur. When males must be pastured together, it is wise to trim down the large fang-like teeth used in fights, called "fighting teeth". Although alpacas may try to bite each other, they only have a bottom row of teeth, so damage is usually minimal. When fighting they will often tangle others necks and attempt to push each other around, but they settle down after a week, as they establish dominance.
When alpacas breed, males make a similar noise called an "orgle". This is thought to possibly stimulate ovulation in the female. This can sound like a warbling or gargling noise in the back or the throat, possibly generated by movement of the tongue.