The Two and Three-Toed Sloths


Ranging from Honduras across South America to Argentina, sloths are another of nature’s strange mammals.  There are two families containing a single genus each:  three-toed sloths, Bradypus, and two-toed sloths, Choloepus.

Unique characteristics of sloths include toe attachment and three recurved claws on each forelimb which allow them the habit of hanging upside down from all limbs, awake or sleeping.  Their hair is different from other mammals in two ways: first, hairs have very tiny grooves which allow for attachment and growth of blue-green algae.  Algae give sloths a greenish hue to their fur, which provides a camouflage while hanging upside down high in the trees.  Secondly, hair patterns flow from the central stomach area to the back, allowing rain to shed off the belly while hanging upside down.  They have a low center of gravity, contributing to very slow and deliberate movements.  Adults weigh from five to 15 pounds and are mostly brown in coloration and are 12 to 20 inches in length.

Sloths are arboreal, meaning that they live in trees and are active during the day and night.  They have a low metabolic rate and low body core temperatures.  This is probably due to their diet of leaves which digest slowly and have rather low content of nutrients.  Stomachs of sloths are divided into compartments.  Leaves ferment in these compartments and in the small intestine where bacteria decompose leaves and perforate cellulose cell walls.  Although sloths spend the majority of their lives in trees, they descend to the earth several times a week to eliminate body wastes.  Sloths tolerate humans and are often found as residents of parks and other places near human populations.  I remember seeing a sloth in a tree near a bus stop in Brazil.  The most notable thing about it was its upside down demeanor and very slow movements.

Sloths may harbor arthropod-borne viruses, such as yellow fever, St. Louis encephalitis, ilheus virus and Venzuelan encephalitis.  These may circulate in their bloodstream for long periods of time, allowing transmission of disease to mosquitoes to humans or other animals.  In Panama, two-toed sloths host causative organisms of leishmaniasis in humans.

A single young sloth is born after a gestation period of about six months.  It remains dependent upon its mother for food for approximately four weeks and is carried around on the mother’s back.  The young remains with her about six months.  Since sloths depend on leaves as food, they are found where most trees keep their leaves throughout the year.  Their home range is about three to four acres.  Sloths maintain desired body temperatures by moving in and out of the sun. They are prey to Harpy Eagles, the largest birds of prey in the Amazon rain forest, but otherwise have a very low mortality rate as evidenced by their low reproductivity.


Lord, R.D.  2007.  Mammals of South America.  The John Hopkins University Press, Baltimore.  198 p.

Redford, K.H. and J. F. Eisenberg.  1992.  Mammals of the Neotropics:  The Southern Cone.  Vol. 2.  The University of Chicago Press, Chicago and London.