I'm a big fan of snakes! When I was a teenager, I had a boa constrictor as a pet and I had to feed it live mice. I would watch the boa kill the mouse and then swallow it whole. There would be this big lump in its body. Then over the next few days, the lump gradually disappeared as the snake digested its meal.
But what about snakes that live in the wild and hunt at night? Can they see in the dark? Or do they use some other way of finding their prey?
It turns out that snakes such as pit vipers, pythons, boas and other animals like bats and some insects hunt in total darkness and sense their prey by detecting the heat the animal gives off.
So, imagine you're that snake. You can sense that your dinner is nearby and you can quietly slither up pretty close to it but can you tell which end is which and how big it is and so forth?
It turns out that you can but up until now, we didn't know how.
Faezeh Darbanian and colleagues, researchers at Rutgers University, set out to uncover just how these creatures did that and offer their results in a paper they published in Matter a few years ago entitled "Soft Matter Mechanics and the Mechanisms Underpinning the Infrared Vision of Snakes".
Let's look at what they did and see what they found.
What We Already Knew
All animals have temperature sensitivity that allows them to differentiate between warm and cold environments. But some animals have evolved a much more sensitive and discriminating ability. By combining temperature sensing with sight they can actually "see" a precise, detailed thermal image.
In fact, their heat sensors are better than the most sensitive human-made ones. As the authors state; "an animal warmer by 10°C compared with the ambient temperature that makes only a fleeting appearance (a mere half a second) at a distance of 40 cm (16 in) can be detected by pit vipers".
Ok, that's a WOW!
So how do snakes sense heat?
Researchers uncovered this decades ago. Some kinds of snakes use a sensor under their eyes called the pit organ. Here's a picture of one taken from this article.
The organ detects the heat as infrared radiation. Inside the pit organ is a thin membrane that separates it into inner and outer cavities. This membrane is what detects the infrared radiation. Not all snakes have pit organs or these membranes.
Here's a cartoon illustrating a pit organ.
Additional studies found that the nerve fibres radiating from the pit organ were enriched in a protein called TRPA1. Snakes without pit organs had much lower levels of TRPA1. This proteins forms small channels that ions can pass through along the nerve. When the temperature changes, even by small amounts, the channels open, charged calcium ions (Ca2+) pass through and a current is established.
That's all well and good but how does that current result in prey detection?
What the heck are pyroelectrics?
Here's what Wikipedia has to say about them.
"Pyroelectricity can be described as the ability of certain materials to generate a temporary voltage when they are heated or cooled. The change in temperature modifies the positions of the atoms slightly within the crystal structure, such that the polarization of the material changes. This polarization change gives rise to a voltage across the crystal."
Aha! Could this be how the pit organ converts heat changes into an electrical signal that the snake's brain recognizes?
The Proposed Model
Here's where their science gets a bit too involved for most lay readers including myself! So I'll try to summarize it as best I can.
What the team did was to develop a mathematical model that treated the pit membrane as a film that changes its thickness in response to changes in heat. The model proposed that when it thickens, the voltage charges would increase enough that the nerve cells could detect and transmit them as electrical pulses.
They developed a series of mathematical equations and formulas that mimicked the snake response times when tested with values that snakes would encounter in the real world.
They freely admit "Like most biophysical problems, we face uncertainty in the precise values of the model parameters."
Which is another way of saying that they haven't actually proved anything yet. But this is the way science works. Especially biophysical work like this. They have given scientists a hypothesis and model that is ready for more testing. Whether it is proven as is or altered as more data becomes available is anyone's guess right now.
What they have done is come up with a pretty darn good interim answer to a long-standing question in biophysics: "what is the mechanism that leads to the conversion of [the infrared] signature into an electrical signal?"
And they have opened the doors to the possibility of exciting new technologies to create artificial materials that have these kind of pyroelectric properties.
I still like snakes and they're even more fascinating than I dreamed of when I was in my younger years.
I knew nothing about their pit organs or their ability to "see" prey in total darkness. I just liked the way it felt when I held them and my boa wrapped itself around my neck or my arm. And I liked to watch snakes in the wild slither away when I came across them.
Luckily, I never encountered an upset rattle snake!
I hope you enjoyed reading this post as much as I did researching and writing it.
Until next time,
Hey, if you enjoyed this article you might like these two that I published on Medium:
- Soft Matter Mechanics and the Mechanisms Underpinning the Infrared Vision of Snakes by Faezeh Darbaniyan et al., in Matter (Oct 2020)
- Originally published as Snake Eyes by Harini Barath in Scientific American (Feb 2021)