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IGUANA  •  VOLUME 14, NUMBER 2  •  JUNE 2007 117HISTORICAL PERSPECTIVES

to which they belong. It is natural enough that a part of the
body situated at one of the regions of manifold relations as the
tail is, and unappropriated to any special function, should be put
to use in various ways, as a prehensile instrument by some mon-
keys and other animals, or a building tool by the beavers, as a
fly-brush by many others, etc.

Mr. Herbert Spencer has already suggested that the wag-
ging of the dog’s tail and similar movements of that appendage
is in fact an escape of nervous force restrained from other modes
of expression at the moment. Looking at the matter from this
point of view, which is doubtless quite satisfactory, we may rec-
oncile it perfectly with the views which have just been presented
by supposing that the ancient and no longer functional channel
of escape for nervous force, the tail, has remained the way of
outlet for the suppressed energy of the animal. The older the
channel the less easy it is to close it either by volition or by nat-
ural selection.

Be the cause of the persistence of the tail and its movement
what it may, we are still justified in assuming as the starting
point, that the progenitor of the rattlesnake had the alternating
motion of the tail common among snakes. It is the opinion of
some herpetologists that the rattles are the remains of the skins
successively shed by the animal. The rate of development of the
rattles, together with the fact that the skins of some serpents are
more imperfectly detached from the region about the tail than

at other parts of the body, makes this view very probable. Let us
suppose that we had a group of poison-fanged serpents, acciden-
tally tending to keep the tail skin in the peculiar fashion of rat-
tlesnakes and that in some of these it was persistent enough to
make the whirring sound of the Cicada when the tail was rap-
idly moved under excitement. These would survive and breed
the most surely and so that feature would become hereditary.
The great variability in the number of rattles in the different
forms of rattlesnakes and the late time of their development,
even among those which differ in no other regard, would seem
to indicate that this structure has not yet been firmly fixed by
long inheritance.

The reader will please not suppose that because I have
boldly followed the lead of the most advanced of the champions
of natural selection that I am convinced of its sufficiency as an
explanation of the great diversities which exist among animals
or of its being sufficient basis for an explanation of the snake’s
rattle. But having been driven step by step from a decided oppo-
sition of the whole theory and compelled to accept it as a vera
causa, though I think one much more limited in its action
among animals than Mr. Darwin believes, I feel it to be my duty
to examine every one of those points upon which I have relied
for evidence against it.

It must be confessed that the case of the rattlesnake seems to
me no longer the bar to the acceptance of the theory it once did.

It seems that the singular structure from which the subject of
these notes derives its name, was intended as a special stum-

bling block in the path of antidarwinists, or to intensify the
“struggle for existence” which the Darwinian theory, like all
other theories must undergo.

In most notices I have seen of the rattles of the rattlesnake,
they have been mentioned as though they were of no advantage
to the possessor, and that natural selection would never produce
them but on the contrary would weed them out, if that theory
were correct. It seems to me that the whole trouble in the matter
arises from the assumption that the sound of the rattles, as a war-
cry, is a disadvantage to the reptile, by calling the attention of its
enemies to it and thus inviting its own destruction, and that con-
sequently the only way to reconcile the existence of the rattles with
the theory of Darwin, is to show that there is some other use made
of them and that in striking the balance between the profit and
loss sides of the ledger, the line falls on the side of the former and
for that reason natural selection produced and retains the rattles.
If I understand him rightly, this is the view of the matter taken by
Prof. N. S. Shaler in his paper in the January NATURALIST. He says
that for some years he has “been teaching that the tail appendage
of the rattlesnake was not to be explained upon the theory of nat-
ural selection, inasmuch as it could contribute in no way to the
advantage of the animal; that is seemed to him quite clear that it
was rather calculated to hinder than to help the creature in the race
of life by warning its prey of its presence.” But he intimates that
he is now ready to say, that this appendage can be explained upon

Use of the Rattles of the Rattlesnake5

J. G. Henderson

5 Reprinted from The American Naturalist 6:260–263 (May 1872).

J. G. Henderson, also in 1872, disputed Shaler’s assumption that rat-
tles were used to attract prey and proposed instead that they serve as a
warning directed at potential predators. Many of his observations were
of Western Massasaugas (Sisturus catenatus tergeminus), at that time
placed in the genus Crotalophorus. 

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the theory of natural selection. He considers the idea that it might
be used as a sexual call as untenable, but that the whirring sound
of the rattles closely imitates the sound made by the Cicada and
for this reason is used as a call-note, as a hunter uses his bone-
turkey-caller, to induce the bird to come within the range of his
weapon. Now the first question which naturally arises is this: Does
the snake sound its rattles when seeking to capture its prey? I have
always understood that it is only when it throws itself upon the
defensive and prepares for battle that the rattles are sounded; that
it is an alarm note, a war-cry, and not a gentle, deceptive invita-
tion to the victim. I have never seen a rattlesnake, and know of
course nothing personally of its habits. But if this use is not made
of the rattles as suggested by Prof. Shaler, and the sound only
serves to call the attention of its enemies and thus invite destruc-
tion, then indeed is the theory of natural selection nonplussed.
But as I view the matter, instead of inviting his destruction by
sounding the rattles, it is one of the most effective means of self
protection and is as useful to it in the race for life as is the growl
of the tiger when threatened with danger. The snake does not
sound its rattles until it considers itself discovered, and not then
unless it apprehends danger. It throws itself in position to strike
and says in unmistakable language, “Look out, I am ready for
you!” If pushed upon, it makes its leap at its antagonist, and again

throws itself in position to renew the conflict, and again sounds
the note of defiance; a note calculated to alarm and, like the war-
whoop of the Indian, strike terror to the heart of the assailant; but
it may be said that the Indian only utters his yells when rushing
on his enemy, or when actually engaged in the conflict, and the
sounding of the rattles upon the first approach of danger is a dis-
advantage. Now it seems to me, if this were true and if it be a piece
of rashness upon the part of the snake thus early to exhibit his
combatativeness, that natural selection would cure the matter by
selecting and preserving the more timid, and that, eventually, rat-
tlesnakes would only sound their tail-bells when it would best pro-
mote their interests.

We are not to judge of the advantage or disadvantage of the
rattles by their effect upon the nerves of man alone, though no
doubt many a man has turned his back and been deterred from
making an attack by the sound of these rattles and the defiant
attitude of their possessor.

The ability of the snake to defend itself does not consist in
its strength or size, or in its power of overcoming its adversary
by a prolonged conflict, for most of its enemies are its superior
in size and strength. Nor does its deadly poison act quickly
enough to secure its own safety when it is attacked, but, in most
cases, the victim, after the deadly stroke is given may still revenge

118 IGUANA  •  VOLUME 14, NUMBER 2  •  JUNE 2007 HENDERSON

This Western Massasauga (Sisturus catenatus tergeminus) is initiating a strike from a coiled “ambush” position. Rattlesnakes use a sit-and-wait for-
aging strategy, contradicting the contention that the rattles were disoperative because the sound would “warn” potential prey as the snake
approached. Instead, the distinctive “buzz” appears to serve as a warning directed not only at potential predators, but at large grazing mammals
that might inadvertently step on an undetected snake. 

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IGUANA  •  VOLUME 14, NUMBER 2  •  JUNE 2007 119HISTORICAL PERSPECTIVES

itself by the destruction of the snake. But the certainty of the
effect of the poison serves as a warning and is advantageous, not
in defense after the attack is made, but in preventing an attack
from being made. If, then, the color of the rattlesnake were dif-
ferent from all harmless snakes, so much so as to render it con-
spicuous, this would be beneficial to it, by the readiness with
which all animals would recognize it, and thus protect the snake
by this notice of the deadly character of its weapons. If then a
conspicuous color would be of advantage, it seems to me that
any other means which it may be able to use in making known
its character to any animal that may come near it, would be
advantageous, and would be increased and preserved by natural
selection, and that the whirring noise which it produces, in this
view of the matter, admirably serves its purpose. In effect it
amounts to this, and by experience its enemies learn to under-
stand its language, “I am a rattlesnake, armed with what will be
death to you if you come too near; give me a wide berth!”

Prof. Shaler remarks that it is a fact well known doubtless
to those who have observed serpents, that many when in a state

of excitement vibrate the end of their tail just as the rattlesnake
does. This statement reminded me of a South American species
described by Darwin in his “Voyage of a Naturalist” (vol. i, p.
123, Harper’s ed.), where he says:—

“Of reptiles there are many kinds: one snake (a
Trigonocephalus, or Cophias), from the size of the
poison channel in its fangs, must be very deadly.
Cuvier, in opposition to some other naturalists, makes
this a sub-genus of the rattlesnake, and intermediate
between it and the viper. In conformation of this opin-
ion I observed a fact, which appears to me very curi-
ous and instructive, as showing how every character,
even though it may be in some degree independent of
structure, has a tendency to vary by slow degrees. The
extremity of the tail of this snake is terminated by a
point, which is very slightly enlarged; and as the ani-
mal glides along, it constantly vibrates the last inch;
and this part striking against the dry grass and brush-
wood, produces a rattling noise, which can be dis-
tinctly heard at the distance of six feet. As often as the
animal was irritated or surprised, its tail was shaken;
and the vibrations were extremely rapid. Even as long
as the body retained its irritability, a tendency to this
habitual movement was evident. The Trigonocephalus
has, therefore, in some respects, the structure of a
viper, with the habits of a rattlesnake; the noise, how-
ever, being produced by a simpler device.”

It was these remarks of Darwin that first suggested the problem
of the rattlesnake’s tail to my mind, and, as I had thought con-
siderably about the matter, of course I was deeply interested in
the paper by Prof. Shaler; but I must acknowledge that, while
many of his suggestions are correct and highly valuable, I was
disappointed to find that the only advantageous use, in his esti-
mation, of this tail appendage of the rattlesnake, is an imitative
call-note to allure birds within its reach, and that, otherwise, it
is rather a disadvantage than an advantage to be preserved and
perfected by natural selection. If it is useful for both purposes,
then there is a double reason for the action of natural selection.
If it is not used as an imitative call-note, but is useful in the man-
ner I have pointed out, then I have shown that it is explained by
natural selection.

Iwish to contribute my observations on the rattlesnake, having
been specially favored in opportunities for the study of this

reptile.
Of all the articles that have appeared on the subject in the

NATURALIST that by Mr. Putnam appears to me to present the
most satisfactory theory concerning the use of the rattles. I am
satisfied that one of their uses is to bring the sexes together.

In July, 1869, I was engaged in surveying along the Logan
river in Wayne County, Nebraska. After completing my contract
I devoted a day to investigating the natural history of the neigh-
borhood. While washing a collection of unios at the water’s
edge, I heard the familiar rattle of the Massasauga (Crotalophorus

The Rattle of the Rattlesnake6

Professor Samuel Aughey

6 Reprinted from The American Naturalist 7:85–86 (February 1873).

Prairie Rattlesnakes (Crotalus viridis) were locally abundant across the
Great Plains at the time these articles were written. Many of the rat-
tlesnake encounters reported by pioneers traversing the Oregon and
Mormon trails were with this species. This snake is in a classic “defen-
sive” position.

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