The slow loris is a small, nocturnal primate and the only primate known to be venomous. Venom is extremely rare in mammals, found in only a few species.

Slow lorises live in the rainforests of South and Southeast Asia and include several species. The Sunda slow loris (Nycticebus coucang) is about 27-38 cm (11-15 in) long and weighs roughly 600-700 g (1.3-1.5 lb); even the largest slow lorises barely reach 2 kg (4.4 lb). They have short, woolly fur (often brownish with a dorsal stripe), a very short tail hidden in the coat, and huge forward-facing eyes for excellent night vision.

Those big eyes help them find insects and fruit in the dark. Slow lorises usually creep along branches rather than leap, gripping tightly as they climb. If startled, they may freeze and cover their faces, but can move quickly to snatch prey or evade danger.

Slow lorises are strepsirrhine primates, relatives of lemurs and bushbabies.

Slow lorises do not have fangs or a stinger. Their venom starts at the inner elbow. Each elbow has a brachial gland (brachial means related to the arm) that oozes a strong-smelling oil. When a loris feels threatened, it lifts its arms and licks those patches. Saliva mixes with the oil and “switches on” the venom.

Delivery is clever. In the lower jaw, they have a toothcomb, a set of thin, closely spaced front teeth used for grooming. The venomous saliva wicks along this “comb,” like a paintbrush soaking up water, coating the teeth. If the loris bites, the toxin goes straight into the wound. It is a rare two-step system in mammals: arm to mouth, then bite.

Quick term check: venomous means it injects toxin, like a snake’s bite or a scorpion’s sting. Poisonous means you are harmed by touching or eating it, like a poison frog or a toxic plant. A slow loris is venomous. Touch is not the danger; a primed bite is.