Scientific American 2019-04

66 Scientific American, April 2019

(^1234)

The closer the positive

and the negative, the

stronger the field

Voltage

experienced

by prey

High-voltage

doublet

Involuntary

prey movement

High-voltage

attack volley

Low-voltage

electroreception

Eel’s Voltage Output^500

volts

1 2 3 4

Attack Mode

Like a Taser, an electric eel on the hunt emits pulses of electricity to in ­

capacitate prey. The eel’s zaps activate the motor neurons that control

the prey’s muscles. In this way, the eel can be said to have remote control

over prey. It uses this remote control in two ways: to reveal hidden prey

by making them twitch and then to freeze the prey once they have been

located, preventing escape. The eel can also use its electricity to

track moving prey. And it has evolved an ingenious solution to

a fundamental challenge of operating in the aquatic realm,

where much of the electricity in its stunning strikes

would typically be lost to the surrounding water.

Focused Intensity

Eel’s electric field is what physicists term

a dipole: lines representing forces on a positive

charge originate from the positive head of the

eel and end on the negative tail. The density

of lines indicates the strength of the electric

field at any given point. Bringing the positive

pole closer to the negative pole increases the

field strength between them. The eel does

this by curling its tail around the prey

gripped in its mouth before zapping it.

SOURCES: “ELECTRIC EELS CONCENTRATE

THEIR ELECTRIC FIELD TO INDUCE INVOLUNTARY

FATIGUE IN STRUGGLING PREY,” BY KENNETH C. CATANIA,

IN CURRENT BIOLOGY, VOL. 25, NO. 22; NOVEMBER 16, 2015, AND

“THE SHOCKING PREDATORY STRIKE OF THE ELECTRIC EEL,”

BY KENNETH CATANIA, IN SCIENCE, VOL. 346; DECEMBER 5, 2014

Illustrations by Matthew Twombly