Like many super-heroes, Daredevil has a suitably tragic origin. As a boy, Matt Murdock was hit by a truck carrying radioactive waste. The accident left him blind and accentuated his senses. It also gave him a “radar sense” that allows him to detect objects around him. This ability was originally described as being similar to echolocation, but that was later changed to be more of proximity detector. It was good change.
Organisms like bats that use echolocation emit ultrasonic calls and then listen for the echo. By comparing how long it takes for the echo to return they can determine how far away an object in the environment is, the closer the object the sooner the echo returns. Daredevil does not, however, emit any noise when using this power.
Artwork by Frank Miller. Daredevil (c) Marvel Comics
Daredevil can sense animate and inanimate objects in the environment all around him (including behind him) and he can do so in the dark. His life depends on his ability to sense a pointed gun or a raised knife. In today’s episode we will discuss a knife that can do the same thing.
The weakly electric knife fish (photo credit unknown)
The knife fish found in Africa’s Black Volta River lives in water so murky that, like Daredevil, it is essentially blind. So how does it navigate the rocks and roots of the river, find food and avoid predators? The knife fish generates an electric field around its body. This is a weak field and can’t deliver a high voltage shock like an electric eel. However, the fish can detect anything that enters the field. Here’s how.
The Electric Organ.(figure from PLoS Biology, 2009;7(9): e1000203 DOI: 10.1371/journal.pbio.1000203))
The fish has an organ called the electric organ in it’s tail. The electric organ is highly modified muscle tissue that generates electrical pulses that travel out from its tail and around to the front of the animal. If something enters the knife fish’s electric field it disrupts the flow of these electrical waves and the fish becomes aware of the intruder. Very cool, but it gets better. The fish can tell the difference between an inanimate object and something living based on how much the electrical waves are deflected.
Figure taken from Eckert’s Animal Physiology (4th ed.). It is originally from “Electric Location in Fish” by H.W. Lissman(c) 1963 Scientific America, Inc.
Nonliving materials (like a rock or a rubber tube) tend not to conduct electricity very well. This means they force the fish’s electrical waves to take a big detour one the way from the electric organ to the head. Living things, on the other hand, are full of salt water and are good conductors of electricity, so they only disrupt the knife fish’s electric field a little bit because they conduct the fish’s electrical waves better than the rock (see the image above).
The catch to this is that weakly electric fields only work for critters surrounded by in water. That’s bad news for Daredevil, but great news for anyone who might one day get hit by a nuclear submarine that had a leaky reactor.
