The Biology of Two Headed Snakes

Earlier this month, the Jonesboro Nature Center in Jonesboro, Arkansas, received a bizarre snake that had been rescued near a community college. Only about 10 inches long, photos of the young snake quickly went viral; the snake had two fully-developed, fully-functional heads (pictured below). Arkansas Game and Fish identified the snake as a native canebrake rattlesnake and took the animal in for rehabilitation due to its condition. Once healthy, it will be put on display at the Jonesboro Nature Center.

Two headed snakes are rare but they are far from unheard of. While there is no hard data to estimate the frequency with which polycephaly occurs in the animal kingdom, anecdotal observation suggests that it may occur more commonly in snakes than other taxonomic groups (though it is unknown why or even if that is true). In the wild, these animals often don't survive for too long for a number of reasons; the canebrake surrendered to ADGF was in a deteriorating condition and unlikely to survive much longer on its own. In captivity, with the proper care these animals can live for over 20 years, and are sold for small fortunes by the breeders lucky enough to hatch one. 

So how do these bizarre beasts come to be? It's actually incredibly similar to how conjoined twins occur in humans. Just like other animals, snakes are capable of having twins; in these rare instances, two (or even three!) snakes may hatch from a single egg. However, just as in humans, there are occasions where the identical twins fail to completely separate from one another, resulting in a conjoined twin.

When two headed snakes survive, they are unusual creatures to observe (I have personally seen a couple of these animals and even a two-headed turtle!). Both heads have fully developed brains, and are capable of moving, eating and sensing their environment independently of one another. This creates some big problems for them in the wild; with both animals trying to move independently, the movement of their body is completely uncoordinated. They end up sending signals down to their muscles to do one thing or another thing simultaneously. This makes them easy prey to larger predators, and makes it farm more difficult for them to capture their own prey.

Even in captivity, life for these animals can be quite difficult. In addition to mobility issues, increased competition puts an added pressure on the snake(s?). In the wild, most snakes are fairly solitary and do not really work together (barring some interesting extreme cases); in captivity, the two heads are no different and will look to their own survival. Feeding can become a challenge as each head will fight for food, even stealing food from the other, even despite partially sharing a digestive system. One head may even become more dominant, and can run the risk of starvation if the snake has two separate stomachs. Worst case scenario, especially in species that feed heavily on other snakes, one head may even try to eat the other head. As a result, keepers have to use dividers to prevent the two heads from seeing one another during feeding (obviously, this would still be a big limiting factor in the wild).

These two headed snakes may be the key to increasing our understanding of conjoined twins in humans. Many breeders are now donating their polycephalic hatchlings to biologists and facilities devoted to studying them, how they developed and how they function as two independent yet conjoined individuals. Though they may be at a severe disadvantage to survive in the wild, with the proper care and attention, these animals can live a long, full and (pretty much) normal life in captivity.

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