Squirrel Monkey Profile
The forests of Central and South America are home to some of the most diverse ecosystems on land. Among the thousands of species found here are around 180 species of primate, ranging from the large and ape-like muriquis to the diminutive, 100g pygmy marmoset.
Toward the small end of this spectrum are a group of five monkeys, agile, masked acrobats with prehensile tails almost as long as their bodies.
Squirrel monkeys are worthy members of the canopy community, yet two of the five species are now endangered, and all are in decline.
Squirrel Monkey Facts Overview
| Habitat: | Cloud forests |
| Location: | Central and South America |
| Lifespan: | 15 in the wild, 20 in captivity |
| Size: | Up to 35cm (14 in) long, |
| Weight: | Usually no more than 1.1kg (39oz) |
| Colour: | Golden brown, with green or purple on the back with a white face |
| Diet: | Fruits, insects |
| Predators: | Falcons, snakes and felids |
| Top Speed: | Unknown |
| No. of Species: | 5 |
| Conservation Status: | From Least Concern to Endangered (Black squirrel monkey, IUCN) |
Squirrel monkeys are New World primates, small diurnal monkeys from the exceptionally humid canopies of the Central and Southern American rainforests.
Their small stature makes them popular in the pet trade, and perhaps even worse, prized testing subjects for various medical and non-medical investigations.
They’re known for their dextrous tails and sweaty hands, and the females have a curious appendage between their legs that they use to dominate one another.
Interesting Squirrel Monkey Facts
1. They have prehensile tails
The cartoon depiction of a monkey often includes a fifth limb in the form of a grasping, dextrous tail, sometimes used to hang from the trees.
This isn’t a given in monkeys, and actually, it’s really only spider monkeys who commonly party like that; no Old World monkeys can even grip or support themselves with their tails, and the New World monkeys are varied in this ability.
Squirrel monkeys are one of the more coordinated with their tails, but far from hanging on them, they’re used to hold tools and act as a brace against branches while they move through the canopy.
2. We don’t know where they came from
This group’s fossil and genetic record doesn’t provide any evidence of how squirrel monkeys made it into Central America.
It’s fairly clear that the five species diverged from one another around 1.5 million years ago in South America, long after humans had found their way onto this newly connected continent, and so it’s possible that they brought these monkeys back with them up to the various islands and archipelagos of the Central American tropics. 1
3. They have sweaty palms
As remarkably sweaty animals, we take sweat glands for granted, but many mammals don’t have any, and a lot of those who do have very few, compared to us.
Many mammals have bare patches of skin to help them cool down when it’s too hot. A dog’s nose can’t sweat but is licked to keep it wet for evaporative cooling. Humans took it a step further and made most of their bodies bare and astonishingly leaky so they could venture out into the African plains without exploding with heat.
Squirrel monkeys have bare patches on their hands and feet, and these are the only places with sweat glands, which makes them important for thermoregulation.
Since they live in hot and humid habitats, sweating isn’t always enough. 2
4. So, they pee on themselves
When sweating isn’t quite cutting it, squirrel monkeys engage in a behaviour that has really gone out of fashion in human communities of late. They pee on their hands and feet and spread it around to help them cool down.
This works for evaporative cooling, whether you’re a monkey or not, it’s just not going to win you any friends. 3
5. Evaporation doesn’t always work
These little monkeys live in some of the most humid environments you can get. Evaporative cooling only works when there’s evaporation, and when the air is already almost saturated at over 95% humidity, there’s nowhere for sweat – or urine – to evaporate to.
It’s unclear how the monkeys handle cooling in the wet season, but it’s clear that their water intake drops as evaporative cooling becomes almost useless. This suggests that switching to alternate means of losing heat, and urine flow rates drop off significantly. 4
6. They have pseudo-penises!
And they’re apparently really proud of them. Female squirrel monkeys will display their exaggerated clitorises at one another to assert dominance.
These features appear to be erectile, and the size of the pseudo penis is controlled by hormones, something which was discovered in lab settings using monkeys who’d had their ovaries removed for science. 5
7. They’re used in lab research
It’s a sad fact that squirrel monkeys are historically one of the most common lab animals to have various things done to them in the name of science.
In the US, they’re still the most common Neotropical primates found in labs and are popular because they’re small and easy to handle.
But far from being valuable martyrs to our quest for cancer cures, a lot of animal testing is still frivolous and inexcusable.
8. Much of this is unconscionable
Even in an ideal setting, there are legitimate arguments around using other animals as a proxy for testing products and medicines. Heavy regulation is a bare minimum when it comes to the complicated ethics around these things, but in reality, regulation isn’t enough.
In a high-profile case in which several nicotine-addicted squirrel monkeys were killed in a lab, an FDA investigation exposed a lack of oversight that led to repeated deficiencies in the care of the animals.
The reality of animal testing is that even if its necessity could be justified in general, it remains a shrouded practice with poorly enforced, reactive checks and balances, and many animals slip through the cracks, experiencing tremendous suffering.
Squirrel Monkey Fact-File Summary
Scientific Classification
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Mammalia |
| Order: | Simiiformes |
| Family: | Cebidae |
Fact Sources & References
- Kenneth L. Chiou (2011), “Pleistocene diversification of living squirrel monkeys (Saimiri spp.) inferred from complete mitochondrial genome sequences”, Science Direct.
- “HUMBOLDT’S SQUIRREL MONKEY”, New England Primate Conservancy.
- “Primate Report”, German Primate Center.
- (1986), “The effect of relative humidity on osmoregulation in the squirrel monkey (Saimiri sciureus)”, Springer Link.
- Wilson, M. I. (1977), “A Note on the External Genitalia of Female Squirrel Monkeys (Saimiri sciureus)”, Journal of Medical Primatology.