Like many other lemur species, black lemurs spend a lot of time in trees. But they also regularly venture to the ground. Therefore, they are both arboreal and terrestrial. And while they are most active during daylight hours (diurnal behavior), with peak activity occurring during the morning and late afternoon, they are also active during evening hours (nocturnal behavior). Thus, scientists have characterized the species as “cathemeral”: referring to an activity pattern that is neither strictly diurnal or nocturnal, nor crepuscular (active during dawn and dusk), but irregularly active at any time of day or night according to environmental circumstances.

Guided by a keen sense of smell, black lemurs advance by running along branches quadrupedally, using all four limbs. (They leave the vertical clinging and leaping to their sifaka lemur cousins.) Characteristic of lemurs, they are fitted with opposable thumbs and big toes that allow them to grasp branches as they travel. Instead of claws, they have fingernails and toenails—except for a specialized grooming claw, also called a “toilet claw” on their second toe. Their long tails help them to balance as they bound through their treed environment. When on the ground, black lemurs might travel bipedally (upright, on two legs) for short periods.

Daytime foraging occurs in the forest understory, which helps to conceal the black lemurs from predators. Predators include fossas (Cryptoprocta ferox), cat-like mammals closely related to the mongoose and the main natural predators of lemurs; harrier hawks (known to swoop down and grab infant black lemurs from the backs of their mothers), civets, and large snakes such as boa constrictors.

Nighttime foraging occurs in the upper and middle canopy and is most prevalent when the moon is brightest. Scientists speculate that, unlike other lemurs, black lemurs most likely lack the eye structure known as a tapetum lucidum, which allows light to reflect through the retina for enhanced night vision. Therefore, bright moonlight helps illuminate the lemurs’ surroundings as they travel in darkness.

In degraded habitats, they might be forced to forage on the ground or even eat dirt—a practice known as geophagia. One possible reason for this practice, wildlife biologists posit, is that the dirt provides essential minerals lacking in the black lemurs’ diet.

As you might imagine, life in the rainforest can be buggy. Not to worry. Those millipede snacks that black lemurs eat provide more than supplemental nutrition; the worm-like arthropods act as insect repellent. As lemurs bite into a millipede’s exoskeleton, the creature releases its natural toxins in self-defense. The lemurs then rub the toxins all over their bodies and through their thick fur coats to keep insects away. But there’s yet another reason why black lemurs might snack on millipedes: the arthropod’s natural toxins act as a narcotic when ingested, inducing pleasurable psychoactive effects—so black lemurs are getting high!

When it comes time to sleep, black lemurs either choose a comfortable tree branch or ensconce themselves inside a tree hole. They choose large trees with thick leaf cover for predator avoidance.