These charismatic creatures have a reputation as nature’s laziest animals, but their slow approach to life helps to keep them safe in a dangerous world
Words Laura Mears
BROWN-THROATED THREE-TOED SLOTH
Bradypus variegatus
Class Mammalia
Territory Central and South America
Diet Fruits, leaves, twigs and flowers
Lifespan 30–40 years
Adult weight 2.3–6.3kg (5–13.9lb)
Conservation Status
LEAST CONCERN
Inside a three-toed sloth
A series of clever adaptations minimise the amount of energy sloths use and maximise the amount of energy they take in. Life in the slow lane would not be possible without their unusual body plan.
Feet for dangling
Depending on the species, sloths have two or three toes, which form hook-like structures adapted for hanging from trees. The ends of their toes and their claws are rigid, so they rely on their flexible wrist joints for movement.
Upside-down adaptation
Sloths have sheets of fibrous tissue that link their liver and stomach to their ribs and their kidneys to their hips. This stops the organs pressing on their lungs when they’re hanging upside down in trees.
Chambered stomach
Sloths have enormous stomachs with four separate chambers. The organ takes up most of the space in their abdomen. Bacteria ferment their food, which can take up to a month to digest.
Low temperature
Keeping a constant body temperature costs energy, so sloths let theirs vary with the air temperature.
Low muscle
Sloths have around 30 per cent less muscle than other animals, helping them to save energy.
Large eye sockets
Sloths have large eyes but poor eyesight. They are most active at night.
Long intestines
It can take up to a week for a sloth’s food to move through its intestines. This helps it to extract as much nutrition as possible from the leaves.
Colon and rectum
Sloths only go to the toilet once a week. Up to 30 per cent of their body weight is food and waste, which is stored up between trips to the ground.
Parasite defence
Sloth fur is dense and fine on the inside and long and cracked on the outside. Antibacterial fungi live in the outer layers, providing protection against disease.
Algae
The green colouring on a sloth’s fur isn’t dirt or pigment – it’s living algae. The organism thrives in the damp, sheltered environment and helps keep the sloth camouflaged.
Mobile ecosystem
Lots of organisms live in sloth fur, including moths, beetles and fungi. Birds, like brown jays, use sloths as a moving buffet, landing on their backs to eat the insects.
INFANCY
Aerial birth
0 days
Sloths give birth upside down. The baby clings to its mother’s stomach.
High-fat milk
0–4 weeks
Sloth milk is around seven per cent fat, providing all the nutrition an infant needs.
JUVENILE
Going upside down
3–4 weeks
After around four weeks the infant sloth is ready to try hanging upside down.
Reaching for leaves
1–6 months
For the first six months baby stays on mum and grasps at nearby leaves.
MATURITY
