I'd like to tip my hat to this week's fortnightly challenge with this question by revisiting an old one.

I asked a question about the Science behind a naturally invisible creature a while ago. At the time, I was handwaving the evolutionary concerns of my Sneaky Devils and looking only at the end result. From the answer to that question, I reengineered my Sneaky Devils so they constantly emitted a magnetic field specifically designed to interfere/disrupt the visual processing of nearby creatures (induced hemianopsia), but which has no effect on similarly developed creatures (they can't force each other to ignore the other).

Suppose that a prey creature developed in this fashion. What would be the evolutionary concerns guiding its development?

I've asked a question here about such a predatory creature. How might a prey creature differ in its evolution from a predator if both display the same sensory-disrupting capacity?

  • $\begingroup$ It could simply evolve the same response.....since creatures producing the magnetic field can't be effected.....or do you want the prey to be invisible for your Sneaky Devils? $\endgroup$ – JDSweetBeat Apr 20 '15 at 16:09
  • $\begingroup$ @DJMethaneMan I want predator and prey to be on equal footing during the hunt, at least in terms of invisibility. I want them to be able to see each other. $\endgroup$ – Frostfyre Apr 20 '15 at 16:11


As our friend Darwin has told us in his famous theory, traits which confer advantages give that group of animals an edge. That edge is transferred to their offspring, and those without those traits do not produce enough offspring, and that new trait eventually becomes the norm for that population.

There are issues with such sensory-blocking magnetic fields, issues that nature already has a solution to. In short, creatures armed with echolocation or electroreceptors can chomp up your sneaky devils. Such solutions would make your sneaky devil invisibility neat, but not advantageous enough to confer advantage to, and therefore development of that trait may not continue.


Sharks and Rays have these organs called Ampullae of Lorenzini. They help these creatures detect electrons firing as they cause muscles to contract.

If your creature emitted magnetic/electric fields, chances are they light up like a beacon to a creature with Ampullae of Lorenzini. Not only would they light up, but these creatures can use these receptors are sensitive enough to guide the fish to its prey and chomp down on it. Turning off their eyesight-disrupting magnetic fields needs to happen or the sneaky devils do not stand a chance.


Bats use echolocation to eat up insects in the middle of the night. A similar level of sensitivity will allow hypothetical predators to find and eat that prey. As bones and organs are not really magnetic, the fields produced by the sneaky devils will not affect them. Sneaky devils will also need to blend into their surroundings to avoid such a predator.

Energy Expenditure

Creatures must also weigh the possible energy expenditure of such abilities. Maintaining such a strong electric field costs a lot of energy; the sneaky devils need a high-energy source of food to afford this. Of course, they could evolve the ability to turn it on or off, but it is still a lot of energy.

  • $\begingroup$ I surmised the extra energy could come from absorbing energy directly from the sun, which isn't a yellow star like ours. Still, you raise good points about the viability of such a creature. $\endgroup$ – Frostfyre Apr 20 '15 at 20:06
  • $\begingroup$ @Frostfyre energy obserbed from the sun will be less dependent on type of sun then on closeness to it and atmosphere. However, keep in mind energy can be used for many things. Even if your creatures get extra energy from the sun through photosynthesis it would likely make sense to put that energy into producing lots of young faster, so that their kids can spread their genetics, then to active defenses that predators will evolve around quickly. $\endgroup$ – dsollen Apr 20 '15 at 20:25

The obvious concerns that would drive this creature are not wanting to be eaten. The same reason that both predator and prey use camouflage.

However, I'm not sure it's realistic to evolve. Camouflage is a much 'cheaper' evolution, that works just as well the majority of time. The energy cost alone of constantly generating that extra electromagnetic radiation would be, well not impossible but definitely an additional expense; and that is before you get into how difficult it would be to evolve a way to know what to emit that will appropriately block your predators vision, do you want to block all vision of every creature, if so how does your mate find you etc etc? Camouflage is a passive protection that is almost as good for far less cost; and is much easier to evolve!

Plus, if someone did evolve this a creature would simply evolve the use of sound or smell as a primary means of hunting and killing the prey species.

  • $\begingroup$ I did mention in the question that similarly-developed species can perceive each other unimpeded. This would allow super predators to exist to hunt these super prey (is that a term?) which are mostly unknown to regular predators. Still, you raise good points about the viability of such a creature. $\endgroup$ – Frostfyre Apr 20 '15 at 20:09
  • $\begingroup$ @Frostfyre yes, however, as I stated it would require a high expenditure of energy to maintain this sort of invisibility. If your primary predators can see and hunt you anyways there is even less reason to constantly expend massive energy on protection that fails to defend against those that would eat you. At least with predator's you could claim they can turn it on and off, so they only expend energy when hunting. $\endgroup$ – dsollen Apr 20 '15 at 20:22

To add onto Pipperchip's comment above, your prey animal also needs to lack a smell, and be able to keep it unsmelly. Another tactic would be mimicry of smells.


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