The teeth in its lower jaw form a comb-like structure called a toothcomb that is used for scraping resin from tree bark.

[6] In an influential 1953 publication, primatologist William Charles Osman Hill also consolidated all the slow lorises in one species, Nycticebus coucang, and considered other forms distinct at the subspecies level.

Osman Hill thus listed Nycticebus coucang pygmaeus,[7] while acknowledging that "it may be deemed necessary to accede this form specific rank.

"[8] In 1960, Dao Van Tien reported a species from Hòa Bình Province, Vietnam, that he called N. intermedius,[9] but it turned out that his specimens were merely adults of the pygmy slow loris, which had originally been described on the basis of a juvenile.

[12][13] The validity of this opinion was later corroborated by studies of chromosomal structure,[14] genetic distance determined by protein variation at polymorphic loci,[15] and mitochondrial DNA restriction enzyme analysis.

[16][17] Nekaris and Nijman (2022) combined morphological, behavioural, karyotypical and genetic data and suggested that pygmy lorises are best placed in their own genus, Xanthonycticebus.

The weight gains, achieved largely by increasing food intake, are triggered by changes in the length of the day and night.

This seasonal change in bodyweight occurs in both sexes, in both pregnant and non-pregnant females—an adaptation thought to help ensure survival during winter when food resources become scarce.

[23] The presence or absence of a dorsal stripe and silvery hair tips appear to be a seasonal variation and have led some to postulate the existence of an additional species, N. intermedius,[31][32] although DNA analysis has since confirmed this to be an adult version of the pygmy slow loris.

[60] A Vietnamese study concluded that the diet of the pygmy slow loris consists largely of tree exudates (gum) (63%) and animal prey (33%), with other food types making up the remainder.

The pygmy slow loris is a specialized gummivore,[63] a trait that helps it overcome difficulties in finding food during times of shortage.

Having generalist dietary preferences allows them to overcome difficult environmental conditions; gum allows them to live at a low energy level with a reduced metabolism.

[64] Trees from which exudates are eaten are from the following families: Sapindaceae (Sapindus), Euphorbiaceae (Vernicia), Fabaceae (Saraca), Anacardiaceae (Spondias), and Burseraceae.

[25] Feeding on gum takes place over a time period ranging from one to twenty minutes and involves intense licking, sometimes accompanied by audible scratching and bark-breaking sounds.

[69] The pygmy slow loris is nocturnal and arboreal, and is most commonly found in semi-evergreen, secondary,[70][71][72] and mixed deciduous forests.

[73] It is distributed east of the Mekong River in Vietnam, eastern Cambodia, Laos, and Yunnan province in southern China.

[72] In Vietnam, the pygmy slow loris was widespread throughout the country,[75] but concern is increasing with conservation and rehabilitation efforts in Cat Tien National Park.

[77] The pygmy slow loris has declined in numbers as a result of extensive habitat degradation throughout its range, including north-eastern Cambodia, the Yunnan Province of China, and Vietnam.

[59] Due to a combination of unstable political situations in its range, and its nocturnal, arboreal lifestyle, population data for the pygmy slow loris are scarce.

[84][82] Within its geographic range and neighbor countries, the trade in the pygmy slow loris has recently increased due to economic changes and human population growth,[85] and the trend is expected to continue.

[72] Decreased sightings in the field and at animal markets indicate that wild populations are being depleted since the low reproduction rate of the pygmy slow loris cannot keep pace with these large-scale off-takes.

[82] Between 1998 and 2006, 70% of pygmy slow lorises seized by authorities died before reaching a sheltering zoo, resulting in replacement demand and additional captures from the wild.

[88] Within the whole Indochinese region, populations of the pygmy slow loris have drastically decreased as a result of military activities, defoliant spraying, logging, and massive off-takes,[89] especially in Vietnam.

The decreasing number of pygmy slow lorises for sale corroborates reports of rapid declines in Vietnamese populations.

By 2007, field sightings were becoming scarce, and there were reports that it had disappeared from large parts of its range,[87] particularly in areas with intense logging and agriculture.

[2] In addition, since October 2001, the European Union prohibits imports for all wild specimens of pygmy slow loris from Laos and Cambodia for conservation reasons.

[83] In Vietnam, confiscated pygmy lorises are usually taken to the Endangered Primate Rescue Centre in Cúc Phương National Park, to be reintroduced into the wild.

Formerly, hundreds of pygmy lorises were traded monthly in major markets,[91] but recently numbers seem to have decreased, due to shortages in supply.

[87] In Vietnam, medicine such as bone glue of monkey, is mainly produced by local people, but a smaller portion is also destined for restaurants or sold to visitors.

A year later, several pairs caught from the wild were transferred to zoos in Cincinnati, San Diego, and the Duke Lemur Center.