This post is just a little late for Halloween. Sorry. But last week I lectured on how we see in the dark – it is a nice problem in statistics to show that, remarkably I think, we can detect light even if less than 10 photons are absorbed by our retina. This is possible because a light photon has a lot of energy in it. Photons of infrared light have much less energy in them, which makes detecting infrared light fundamentally harder.
A student asked me about animals detecting infrared, and we both knew snakes could do it. But I learnt today that so can vampire bats. They appear to detect the heat coming off a vein near the surface and zoom in for a feed. Incidentally, on the Wikipedia page I learnt that vampire bats are unusual amongst bats in being able to run, and with the wonders of the internet I was watching a vampire bat running on YouTube. I love the internet.
Anyway, let’s get back to how bats and snakes detect infrared light. There was a paper by Gracheva et al. in Nature last year studying the molecular basis of how infrared detection is done. It is completely different to how we (and snakes and bats, etc) detect light.
Basically these snakes have molecules that are very very sensitive to temperature and so they detect the heat in infrared radiation, and these sensitive thermometers are in pits which shield them from infrared radiation except from straight ahead which makes the detection directional.
This is nowhere near as sensitive or as accurate as vision is for visible light, but of course it works at night, which is handy for snakes hunting warm mice, and vampire bats looking for veins. Given that it works by detecting the tiny temperature rise due to arriving infrared radiation from a mouse that could be a metre away, I am impressed that it works at all. Evolution is a powerful thing, and it makes some fantastic detectors.
Apparently the Western Diamondback rattlesnake is particularly good at detecting infrared radiation, so it is probably best to avoid these on all dark nights, not just Halloween.
