You might have heard it as a fun fact: an ant could survive in a microwave if it could see the waves, because microwaves are broad enough frequency that an ant – given perfect timing – could fit between the crests of the waves.
If given perfect timing, perfect height, and perfect conditions, what other animals could fit through waves? (IRL, though, wave dynamics are one of the toughest fields of physics because the exact way they behave is reliant on quantum mechanics that break down when directly observed. Don’t put living things in the microwave because of theoreticals.)
But First, Amplitude vs. Wavelength
The wavelength of a wave is what determines what category that particular waves fits into – it’s the distance between crests of a wave. Every wave between 380 and 750 nanometers, for example, fits into the visible light spectrum, and if the human eye could decipher such fine differences, you’d see that each adjustment of +1 or -1 nanometer produces a slightly different color until you run out of visible ones.
Meanwhile, amplitude determines the ‘strength’ of the wave, or the distance between the crest and the trough. This does not determine a danger level! You can have long wavelength, high-amplitude radio waves broadcasted out into space, and short wavelength, low amplitude UV rays you can use to cure acrylics on Earth. Both can burn you, but the radio waves will burn you much faster between those two previously mentioned. The bandwidth for Wifi actually overlaps a little with a standard kitchen microwave, but you obviously wouldn’t want to expose yourself to an open, running microwave even though Wifi is likely coursing through your house right now. The amplitude of the microwave is high enough to harm you if not reflected by the microwave’s metal – the WiFi is only strong enough to transmit data about 150 feet.
Additionally, as a very simple explanation, when waves connect with something, they give that something some of their energy and then continue on their way either through the object or reflected off of it. This is why metal starts to glow when heated, even though infrared (or heat) radiation itself does not glow – the metal is accumulating so much energy from the infrared waves that some of the energy it’s re-emitting is visible! (Although it is also still emitting a lot of infrared energy when it gets to that point as well.) The same is true in reverse, and when glow-in-the-dark paint is ‘charged’ with UV light, it’s reflecting some of that light back at a lower wavelength that we can see, even though we can’t see UV rays.
The biggest waves: Radio Waves
Radio Waves eat up a huge portion of the EM spectrum, consuming basically everything that’s below Infrared waves. Radio waves can be emitted by quite a few things, but most commercial radio stations take up 88 to 108 MHz, with commercial users like airports taking up 108 to 136 MHz, and the military (at least in the US) using 225-400 MHz. If you want to switch to AM radio, you’ll get a range of 550 to 1720 KHz, significantly lower.
However, just because a lot of things are called radio waves does not mean all of those things are equal. AM radio can’t penetrate the Earth’s ionosphere so AM radio is trapped on Earth, even though FM radio can get through just fine. Radio waves can range between 62 miles and 0.04 inches across crests – the behavior of the waves changes as the wavelength does, even though all of that is technically radio waves. There’s a distinct point where the ionosphere stops letting radio waves through (around the AM bands) – before that and after that, radio waves can pass through the entire atmosphere just fine. All of these bandwidths are still radio waves.
What fits in between radio wave crests? At the lower end, quite a bit! You could fit the empire state building several times over comfortably between the crests of the lower wavelengths, and that scale goes all the way down to 0.04 inches, fitting everything in between that end and 62 miles. Every living or fossilized animal to have lived on Earth could reasonably fit somewhere on this spectrum. Even going up to FM radio, the distance between wave peaks is approximately 10 feet, so your average person could still fit if you could ‘freeze’ the wave.
At the high end?
Microwaves are technically part of radio waves, but their usefulness earns them their own special chunk of bandwidths, the same way indigo wasn’t its own color until indigo (the plant) got politics involved in defining the colors of the rainbow. Microwaves occupy the range of about 1 millimeter to about 1 meter, overlapping with radio waves above. High-amplitude microwaves can be used to cook food, but low amplitude ones can be used to transmit complex data without cables, aka WiFi. This range in a different measurement system is 300 KHz to 300 GHz, which you’ll notice includes your average 2.4 GHz house Wi-Fi.
Long-wave microwave radiation can pass through the Earth’s atmosphere – short-wave can’t. As for the animals that can fit in the crests, that’s a question of which microwaves you’re referring to! The most common microwaves can fit butterflies, ants, and anything else smaller than 12.5 centimeters, or about 5 inches. In a theoretically perfect environment, these small animals could dodge the microwave.
Infrared waves aren’t visible to humans, but some animals (like snakes) can see them. You may have seen infrared goggles on ghost-hunting shows or in spy movies – infrared waves are a form of EM radiation below the visible spectrum, and a crucial part of our survival. Infrared radiation is what warms the Earth (from the sun) across the vacuum of space – the waves interact with the particles of our planet and it’s atmosphere, transferring the energy (warmth) that most surface creatures need to survive.
Infrared waves are where we get into microscopic territory, coming from 700 nm to 1 mm in bandwidth, right underneath visible light.
A waterbear (or Tardigrade), a small, multicellular life form, could still theoretically dodge these waves unless it’s unusually large. Most of the teeny stuff you’d find living in a lake, like algae, plankton, and amoebas, are in the same camp.
The visible spectrum (and the final “Survivable by Missing” Zone)
The visible spectrum takes up the bandwidths from 360 nm to 700 nm, after which comes ultraviolet light. The smallest organisms often come to a tie due to differences between individuals’ body sizes, but that tie is dominated by bacterium with bodies 200 nm to about 300 nm, many of them parasitic or aquatic. While that technically stretches up a smidge into the UV range, it also means that the smallest living organisms we know of could fit between waves of high frequency blue light. To get technical, the common flu virus ranges in size from 80 to 120 nm – that’s way into UV rays – but it’s not technically alive.
Visible light can also be dangerous! High-amplitude green light used in lasers can permanently damage your eyes and your cameras, and some lasers are used to cut and etch things!
Visible light can also serve as a warning that other forms of radiation are nearby. When you heat metal, that metal begins to accumulate energy – eventually, it starts to glow. The hotter it is, the bluer it gets, until it’s giving off so much light that all your eyes can perceive is white. When things glow in the dark under UV light, what’s happening is that the item’s particles are absorbing the energy from the UV rays and releasing it back out at a lower frequency, one we can see. Many radioactive things glow with little outside input – uranium glass glows a ghostly green under UV, and so does radium, which was commonly used in paint on things like watch faces and the like. Both of these items are absolutely emitting gamma rays, but at such low volumes they’re more or less safe to be around – unless you were the one using the paint at the factory.
That’s all the waves that certain animals could avoid.
Note – just because a certain wavelength of EM Radiation doesn’t kill something, doesn’t mean it’s not hitting it – in the same way our human skin is resistant to destruction by visible light and we’re unaffected by WiFi beaming all around us, some living creatures can survive gamma waves, high-amplitude infrared waves, and more. What’s better is that if the amplitude is low enough, humans can survive exposure to dangerous waves with minimal side effects, as long as it doesn’t happen too often. Think back to uranium glass – it will trigger the Geiger counter, but unless you’ve physically strapped the plate directly to your body long-term, it’s unlikely to give you any trouble. Again, not long-term. See X-rays: your dentist leaves the room for X-rays because you only need them once a year, but the dentist would be exposed every day if they stayed in the same room, and the effect of exposure builds up over time, potentially damaging DNA repeatedly.
Waves behave in ways we struggle to understand fully and so do many animals. Chernobyl’s got some weird molds growing on the inside of the destroyed reactor, and somehow they’re able to absorb the energy from gamma rays without their DNA being disrupted, the way ours is. Who knows – maybe we discover something that can survive being blasted by the sun directly, without the shield of our atmosphere, out in space.
https://en.wikipedia.org/wiki/Smallest_organisms (as a list, Wikipedia is reliable – I could go list each of this list’s source materials individually, but then you wouldn’t be able to see them compared.)