By Alison Freiman

A Sloth Life

My name is Sunshine and I am a three-toed sloth living on the Osa Peninsula of Costa Rica.  Being a sloth, I can sleep an average of 18 hours a day, either hanging upside down from a tree branch or embracing a thick trunk.  



Without any fear of falling I am able to hold my hanging body for long periods of time and even cling to a branch with my hind legs and lean over backwards at a 90° angle.  This is mostly due to the dominance of retractor muscles in my body. These are the muscles responsible for adducting motions.  Many muscles that would normally be extensors in other mammals are modified to function as retractors in my body, giving my limbs a very powerful and efficient grip. 



The bones of my toes are bound together by ligaments and are not separately moveable.  This enables my hands and feet along with my long curved claws to function as a hook, allowing me to suspend my body in the air while I am high up in a tree.


 As I arise from my slumber, I smell the aroma of Cecropia leaves drifting across the river from where I am, although I can not easily see them as a result of my poor eyesight.  Unfortunately, I lack ciliary muscles that help to focus a clear image onto my retina regardless of whether an object is near or far away, a process called accommodation.  In addition, my vision is adapted for low light; I have many rods and very few ganglion cells and cones. 

My nose is more efficient than my eyes.  By sniffing the air, I can tell what direction I need to go to get to my favorite leaves.  When I was a baby clinging to my mother she ate the leaves of the Cecropia tree all the time.  I would lick the leaves off my mother’s lips as she ate.  Young sloths feast on what their mother’s choose to eat and develop similar food preferences. Now as an adult sloth, Cecropia trees are my favorite!

The jaguars should be resting by now; it is late morning, although I always need to be on guard for those harpy eagles that want to eat me.  I do not move very well on the forest floor; I am virtually helpless because I lack the extensor muscles and the stability to support my weight with my limbs. The dominance of retractor muscles in my hind limbs makes me a “four-armed” animal and my legs have no weight bearing capabilities.  

On the other hand, I am quite the accomplished swimmer so I will drop into the river from a low branch and swim to my destination.  My low muscle mass and my oversized, buoyant stomach allows me to float and makes me practically weightless in water.  Using my long arms as paddles I slowly pull myself across the river with very little effort.

As you can see, I am not as graceful on the ground as I am in the trees!

I am now high up in the Cecropia tree...

...happily eating its leaves.  I like to choose the younger leaves because my belly has an easier time digesting them. I tear off the leaves with my lips since I lack incisors and only have 5 simple, peg-like teeth on each side of my upper jaw and 4 on each side of my lower jaw.  As I chew, my long tongue which is densely covered with sharp, minute, backward-directed spines, pushes the leaves to the back of my throat.  Microorganisms are necessary in my belly to break down the highly indigestible cellulose into fatty acids that can then be absorbed into my bloodstream.  My 4-chambered belly allows food to be in different stages of decomposition at all times.

Exhausted from eating, I begin daydreaming about meeting a fine looking male sloth.  Although, my girlfriend sloths and I do not have a specific mating season, I have just turned 4 years old and I am in estrus for the first time.  My screams echoing through the canopy of the forest have attracted a male to my location.  With luck, I will be a proud parent in about 6 months and will raise my offspring in the same way my mother raised me.  As a mother, I will protect my baby for up to 9 months after birth.  I am looking forward to giving birth hanging from a tree in the Osa Peninsula where we sloths are safest and most comfortable. 

As I said before, I must always be aware of my predators, the harpy eagle, the jaguar and sometimes humans.  Algae obtains shelter in my guard hairs turning it a greenish color and in return keeps me invisible high up in the trees.  However, when I have to make those infrequent visits down to the ground, I am in danger and must be very careful.  It has been over 8 days since my last trip down the tree to relieve myself of my metabolic waste and I am overdue.  

One of my very special friends, that bear’s my name, the sloth moth, actually breaks its wings when it crawls into my fur to live on me.  These gals need to crawl off me as I am defecating in order to lay their eggs.  Luckily I do everything very slowly giving them sufficient time to accomplish their task.  My dung also decomposes very slowly which is unusual in this warm, humid climate, giving the larvae plenty of time to develop and feed before they are mature enough to fly off and find another sloth friend to live on.  

Luckily, some humans happen along and are able to scare the eagle off and rescue me from this danger, but I am wounded.  They are kind tourists from Mercy College in Nueva York and they are familiar with a sloth sanctuary in Avarios del Caribe.  I am transported to the sanctuary and my wounds are treated until I am fully healed. 

I am down the tree, making a small depression in the ground, when something grabs me from behind.  From the sharp talons, I can tell it is a harpy eagle and I am in trouble.  I fight back with the only defense I have, my long claws.  The eagle knows I am vulnerable and keeps attacking.  I am hurt, but I do not feel the pain.  My primary and secondary coats are very thick and I have very few pain receptors in my dermis.  

Once again I am 30 meters up in my favorite tree, camouflaged from sight below and surrounded by all the insect life in my fur and on my skin.  I am going to take a very long nap hanging upside down the way I always do.




Anatomical Society of Great Britain and Ireland. Vol. 4. N.p.: Ulan, 2011. Print. Journal of Anatomy and Physiology.


Burns, Taylor. "The Slowness of the Sloth Decoded." Cosmos 28 July 2011: n. pag. Cosmos Online. Web. Sept. 2014.


Craigie, David, and George Aikman. Elements of Anatomy, General, Special, and Comparative: From the Encyclopaedia Britannica, Seventh Edition. Edinburgh: Printed for Adam Black ..., 1831. Print.


Friedrich Schiller University Jena. "Decoding slowness: How sloths perfected energy

saving." ScienceDaily. ScienceDaily, 20 July 2011. 


Giacalone, Jacalyn, Dr.  "Montclair State University." Sloths -. N.p., 1998. Web. 2 Oct. 2014.


Gilmore, D.P., C.P. Da-Costa and D.P.F. Duarte (2000).  “An update on the physiology of two- and three-toed sloths,” Brazilian Journal of Medical and Biological Research Vol. 33, pp. 129-146.


Gilmore, D.P., C.P. Da-Costa and D.P.F. Duarte (2001).  “Sloth biology:  an update on their physiological ecology, behavior and roles as vectors of anthropoids and arboviruses, “ Brazilian Journal of Medical and Biological Research Vol. 34, pp. 9-25.


Goffart, M. (1971).  Form and Function in the Sloth.  Oxford and New York: Pergamon Press.


Harlan, Richard. Observations on the Anatomy of the Sloth: Bradypus Tridactylus, Linn.). N.p.: Harvard U, 1832. 26 Aug. 2008. Web. Oct. 2014.


Hautier, Lionel, Vera Weisbecker, Marcello R. Sanchez-Villagra, Anjali Goswami, and Robert J. Asher. Skeletal Development in Sloths and the Evolution of Mammalian Vertebral Patterning. Vol. 107 No.44. N.p.: PNAS, 2010. PDF.


Holdrege, Craig (1998, 2009 revised).  “What Does It Mean to Be a Sloth?” Newsletter of the Society for the Evolution of Science, Vol. 14, pp. 1-26.


Mendel, Frank C. (1985).  “Use of Hands and Feet of Three-Toed Sloths (Bradypus variegatus) during Climbing and Terrestrial Locomotion,” Journal of Mammalogy, Vol. 66, pp. 359-366.

Mendel, Frank C., David Piggins and Dale R. Fish (1985).  “Vision of Two-Toed Sloths (Choloepus), “ Journal of Mammalogy, Vol. 66, pp. 197-200.


Milius, Susan (2014).  “Sloths, moths, algae may live in three-way benefit pact,” Science News, Vol. 185, p. 11.


Nyakatura, J. A. and Fischer, M. S. (2011), Functional morphology of the muscular sling at the pectoral girdle in tree sloths: convergent morphological solutions to new functional demands?.  Journal of

Anatomy, 219: 360–374. doi: 10.1111/j.1469-7580.2011.01394.x


Riegner, Mark (1998). "Horns, Hooves, Spots, and Stripes: Form and Pattern in Mammals," in Seamon and Zajonc 1998, pp. 177-212.


"Sloth Digestion." Sloth Sanctuary of Costa Rica RSS. N.p., n.d. Web. 3 Oct. 2014.


Sunquist, Fiona (1986). "Secret Energy of the Sloth," International Wildlife vol. 16, pp. 6-10.



Suutari et al. (2010).  “Molecular evidence for a diverse green algal community growing in the hair of sloths and a specific association with Trichophilis welckeri (Chlorophyta, Ulvophyceae),” BMC Evolutionary Biology 2010, 10:86.


YouTube.  “3 Toed Sloth Walking.”  Online video clip.  YouTube, 15 January 2013.  Web.  30 November 2014.

YouTube.  “Mouldy Sloth:  Amazing Animals – Amazon Assassin – BBC Wildlife.”  Online video clip.  YouTube, 24 November 2008.  Web 30 November 2014.

YouTube.  “Sloth Mating Call.”  Online video clip.  YouTube, 13 September 2010.  Web.  30 November 2014.