In Western and Eastern Polynesia Aitu are known as ghosts or spirits, often unkind and malicious.
The word is common to many languages of Western and Eastern Polynesia. In the mythology of Tonga, for example, ʻaitu or ʻeitu are lesser gods, many being patrons of specific villages and families. They often take the form of plants or animals, and are often more cruel than other gods. These trouble-making gods are regarded as having come from Samoa. The Tongan word tangi lauʻaitu means to cry from grief, to lament.
In Māori mythology, the word aitu refers to sickness, calamity, or demons; the related word aituā means misfortune, accident, disaster. In Tahitian, aitu (syn. atua/raitu) can mean 'god' or 'spirit'; in other languages, including Rarotongan, Samoan, Sikaiana, Kapingamarangi, Takuu, Tuamotuan, and Niuean, aitu are ghosts or spirits.
In Cook Islands Aitu is also the name of ancient tribes who came from the east. According to tradition, some of the Aitu tribes settled on the islands of Aitutaki, Atiu and Mangaia. At Aitutaki (Aitu-taki) they were eventually destroyed or driven away. At Mangaia they were from time to time slaughtered in order to provide sacrifice to the gods. There still exists at Mangaia the remains of a great oven named te umu Aitu where large numbers of these people were cooked after being slain.
In the Samoa Islands, aitu also means ghost. In other Austronesian cultures, cognates of aitu include the Micronesian aniti, Bunun hanitu, Filipino and Tao anito, and Malaysian and Indonesian hantu or antu.
Modern Samoans merely claim the aitu to be an evil spirit with a long fang who bites people and thus causes very bad infections, sometimes fatal ones, and even when the bite is not fatal, it leaves a long, hard nifo, “tooth”, that eventually works its way out of the wound.
Samoans today, particularly Western Samoans, still rely on the tala anamua, or ancient stories, to account for numerous features of their cultural life and environment. In both Samoas, but particularly in the American territory, the younger generation’s acceptance of these stories as being literally true, and their belief in aitu, are markedly less pronounced than that of their elders. Nevertheless, many young people in both countries still believe this traditional lore.
A common belief holds that when an aitu enters a living body, it does so through the armpit. It remains there, in the lower abdomen, or in the back of the neck. A person about to be possessed is said suddenly to feel cold or to sense that the ghost is trying to carry his body away. Another symptom of oncoming possession (often cited also by persons who merely claim to have seen an aitu) is the feeling that one's head is “getting very large.” A possessed person's eyes often bulge. Spitting or grimacing is - common.