In the early 1900s, John Still was sitting on his veranda and reading when he heard a strange noise coming from inside his house. It was a heavy breathing, interrupted by an occasional hiss. He recognized it as the sound of a cobra preparing to strike. Still kept a pet loris, which was not in its cage at the time. Worried that the snake might attack it, he grabbed a stick and went to investigate.
“As I went into the room I looked at the cage, which was on the floor, and on the top of it I saw the outline of a cobra sitting up with hood expanded, and threatening a cat who crouched about six feet away,” he later wrote in a letter to a scientific journal.
As his eyes adjusted to the light and he got a better look, he realized there was no snake. The cobra he thought he saw was actually his loris, “who, with his arms and shoulders hunched up, was a sufficiently good imitation of a cobra to take me in, as he swayed on his long legs, and every now and then let out a perfect cobra’s hiss.”
Lorises are some of the most adorable critters around. With their big eyes, short snouts and round ears, the small primates look a little bit like baby Ewoks come to life. Cobras, on the other hand, look like snakes. They’re not fuzzy. Most people wouldn’t call them cute. Yet Still, who was familiar with both animals, confused the two. And he’s not alone. Plenty of other scientists have noted the similarities between snakes and slow lorises (a branch of the loris family) in the way they look, sound, and move. Slow lorises put their hands over their head when threatened in a way that looks, as Still said, like a cobra reared up and spreading its hood. They also have a dark stripe running down their backs that resembles the body of a snake when viewed from above, and use a pant-grunt vocalization that “resembles remarkably the raspy hiss of a cobra.”
Slow lorises have another thing in common with some cobras: They’ve got a nasty bite. The slow loris is often considered one of only seven venomous mammal species in the world, and the only primate that belongs to that club. If you want to get technical, though, it’s more of an honorary member and not a card-carrying venomous animal. They’ve got no venom glands and, instead, their bites are dangerous because the secretions from their brachial glands (a small patch of furless skin on the inside of their elbow), which they lick up and mix with saliva for biting, contain a protein that’s similar in structure to the allergens found in the saliva and glands of domestic cats. In other words, they’re not so much venomous as allergenic, and their gland secretions are toxins “only for certain (incidentally) susceptible species, like humans.”
Whether you want to grant the loris true “venomous” status or not, its bite can cause edema, pain, scarring and, in extreme cases, anaphylactic shock and death. No wonder that people in the animals’ native Indonesia have thought them a little scary. In some parts of the islands, folklore holds that if the blood of a loris touches the ground, a landslide will follow. In other areas, people believed that no plants could grow on ground touched by loris placenta. Elsewhere, warriors would smear their weapons in loris blood, believing it would cause their enemies' wounds to fester and not heal.
Anyway, back to the snakes. In a recent paper in the awesomely-named Journal of Venomous Animals and Toxins including Tropical Diseases, biologist Anne-Isola Nekaris and other researchers make the case that the similarities between slow lorises and snakes aren’t mere coincidence—they’re adaptive, and lorises evolved to mimic cobras.
Plenty of animals masquerade as something they’re not. Mimicry is common among insects, less common in vertebrates, and rare, but not unheard of, in mammals. Some harmless animals look like dangerous ones to confuse predators and make them think twice about attacking. Some venomous or toxic animals look like other venomous or poisonous ones to increase the effectiveness of their warning signals.
Nekaris thinks that lorises are the latter type, called Müllerian mimics. For the venomous (or whatever you want to call it) loris, there’s an advantage to looking like their venomous neighbor, the spectacled cobra, in that the two species share the costs of being attacked and killed by their common predators as the predators learn that they’re both dangerous and should be avoided (while a uniquely patterned and dangerous animal bears those costs on its own).
For this cost-sharing to work, the model, the mimic, and the predator being fooled all have to be in the same place at the same time at some point in their evolutionary history. Nekaris thinks that the loris mimicry evolved around 8 million years ago. Cobras had come to Asia from Africa over a land bridge a few million years before lorises had started showing up in Asia. Around the same time, the climate in Southeast Asia changed and tropical forests gave way to more open savannah-like environment. For the lorises, this meant less time in the trees and more time on the ground, which introduced them to a new group of predators.
“Consequently, the change in predation pressure caused by this adaptive shift may have triggered the move towards mimicry, whereby an advantage from mimicking a predator like Naja naja was gained,” Nekaris and her team write. “For aerial predators in particular, with their vision hampered by long grass, glimpses of the unmistakable markings of a spectacled cobra meandering across the ground between trees may have been enough to deter or at least postpone their intended attack.”
It’s an interesting idea, and of course more work will need to be done to see how right it is. In the meantime, take a look at the image above, from Nekaris’ paper—it’s not hard to believe that an eagle flying overhead or a person in a dark room might mistake a loris for a snake.