Lorises are arboreal primates with large eyes encircled by patches and short index fingers. They constitute the subfamily Lorinae under the family Lorisidae, which also contains pottos and angwantibos.
These mammals are abundant in Southeast Asia, including the islands of Java, Sumatra, and Borneo. They are nocturnal, feeding primarily on leaves, fruits, and gums of trees. Some species, however, are insectivores and consume ants, mites, and termites.
Currently, there are 11 species of lorises, grouped into 3 genera: Loris (Slender lorises), Nycticebus (Slow lorises), and the monotypic Xanthonycticebus, containing the Pygmy slow loris.
The pygmy slow loris, the smallest of all loris species, measures about 10 in (25 cm) in length and weighs around 1 lb (0.45 kg). In contrast, the largest species, the Bengal slow loris, ranges from 10 to 15 in (26 to 38 cm) in length and weighs between 2.2 and 4.6 lb (1 to 2.1 kg).
Slender lorises, by comparison, are usually around 8 to 10 inches (20 to 25 cm) in length, while slow lorises average between 11 and 15 inches (27 to 37 cm).
Lorises have soft, wooly fur that ranges from gray to brown, with their dorsal side being darker than their ventral part. Their large eyes are encircled by dark patches, while their small ears are sometimes hidden beneath the fur.
Slender lorises have long and slender limbs, rounded heads, and pointed muzzles, whereas slow lorises are more robust with shorter and stouter limbs, round muzzles, and smaller ears and eyes.
The forelimbs and hindlimbs of lorises are almost the same length. The arteries and veins in the limbs form networks of intertwining vessels called rete mirabile, which facilitate gaseous exchange and the removal of waste products.
They have opposable thumbs and a characteristically short index finger, with nails on all their digits except for the hindfoot. As strepsirrhines, they also have a grooming (or toilet) claw on the second toe of their hindlimbs.
They have well-developed skulls with distinct temporal ridges, featuring a round braincase with highly reduced anterior parts. The orbits face forward and have wide postorbital processes, while the bullae show moderate inflation.
The zygomatic arches are broad, and the external auditory meatus remains continuous with the zygomatic branch of the squamosal bone.
Their upper canines are long and well-developed, while their anterior lower premolars are canine-like in appearance. The molars are large and bear three to four cusps.
Like most strepsirrhines, lorises, too, have a specially adapted structure called the ‘toothcomb’ in their lower front teeth. This structure helps them groom themselves and even inject their venom into the bodies of their enemies.
Their dental formula is 2.1.3.3/2.1.3.3 = 36.
Lorises belong to the subfamily Lorisinae, which in turn falls under the family Lorisidae. Together with Galagos (family Galagidae), Lorisidae belong to a broader superfamily, Lorisoidea. This superfamily is a sister group to the lemurs of the superfamily Lemuroidea.
Out of the 11 extant species of lorises, two species, gray and red slender lorises, have 4 and 2 subspecies, respectively.
These mammals are found in Southeast Asia, especially in the tropical and woodland forests of India and Sri Lanka. They also inhabit various islands, including Java, Sunda, Borneo, and Sumatra.
The Pygmy slow loris is restricted to the forests in the vicinity of the Mekong River, while the Sunda slow loris inhabits Peninsular Malaysia and Sumatra. The two species of slender lorises are primarily found in India and Sri Lanka.
Although they generally feed on leaves, fruits, and gums, some species, like Gray slender lorises, are insectivores, consuming insects like ants, mites, and termites. This species also feeds on other invertebrates, like mollusks and spiders.
Lorises are nocturnal, foraging at night and resting during the day.
They are arboreal and climb trees with slow and composed, hand-over-hand movements (climbing quadrupedalism) instead of leaping from one branch to the other. However, when necessary, these animals can move rapidly along the branches.
Since their hands and feet are well-suited for grasping, they can move along the underside of branches just as easily as they do at the top.
When threatened, certain lorises, such as the Javan slow loris (the only known venomous primate), secrete oil from a small brachial gland beneath their armpits. They lick this oil to mix it with saliva, creating a toxic venom. If injected into an attacker, this venom causes a necrotic effect, effectively incapacitating it.
In the wild, lorises have an average lifespan of 20 years, while they may survive up to 25 years in captivity.
Lorises have a gestation period of about four to six months, after which they give birth to one or two offspring. The young often cling to the bellies of their mother or wait in their nests when she is busy foraging in the wild. Sometimes, the mothers practice infant parking, in which they coat their babies with allergenic saliva and hide them behind trees and bushes.
In about 3 to 9 months, they are weaned and gradually attain sexual maturity within 10 to 18 months.
These animals are preyed upon by orangutans, snakes, monitor lizards, and birds of prey such as hawks. They are also hunted by humans for food and are commonly used in the pet trade and traditional medicine.
Apart from hunting, these mammals are threatened by habitat loss and fragmentation. According to the IUCN Red List, the eleven species of lorises are grouped under the following categories.
| IUCN Category | Species |
|---|---|
| Near Threatened (NT) | Gray slender loris |
| Endangered (EN) | Greater slow loris, Sumatran slow loris, Bengal slow loris, Red slender loris, Pygmy slow loris |
| Vulnerable (VU) | Philippine slow loris, Kayan River slow loris, Bornean slow loris |
| Critically Endangered (CR) | Bangka slow loris, Javan slow loris |
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