REPTILES, AMPHIBIANS, ETC: Rattlesnakes
Fig. 1. Prairie
rattlesnake, Crotalus viridis viridis
are distinctly American serpents. They all have a
jointed rattle at the tip of the tail, except for one
rare species on an island off the Mexican coast.
This chapter concerns the
genus Crotalus, of the pit viper family Crotalidae,
suborder Serpentes. Since snakes evolved from lizards,
both groups make up the order Squamata.
This article describes the
characteristics of the common species of rattlesnakes
that belong to the genus Crotalus. These include the
eastern diamondback, (C. adamanteus); the western
diamond (back) rattlesnake, (C. atrox); the red diamond
rattlesnake, (C. ruber); the Mohave rattlesnake, (C.
scutulatus); the sidewinder, (C. ceraster); timber
rattlesnake, (C. horridus); three subspecies of the
western rattlesnake, (C. viridis): the prairie
rattlesnake (C. v. viridis); the Great Basin rattlesnake
(C. v. lutosus); and the Pacific rattlesnake (C. v.
*Information pertains to
other poisonous snakes.
There are 15 species of
rattlesnakes in the United States and 25 in Mexico.
Other front-fanged poisonous snakes of the Crotalidae
family, which are not included in this discussion, are
the massasauga and pigmy rattlesnakes, both of the genus
Sistrurus. Also not included are two snakes that do not
have rattles, hence are not called rattlesnakes: the
water moccasin or cottonmouth, and the copperhead, both
of the genus Agkistrodon. Two other genera of poisonous
snakes in North America are coral snakes (Micrurus and
Micruroides) of the family Elapidae.
Rattlesnakes are usually
identified by their warning rattle — a hiss or buzz —
made by the rattles at the tip of their tails. A
rattlesnake is born with a button, or rattler, and
acquires a new rattle section each time it molts.
Rattlesnakes also are distinguished by having rather
flattened, triangular heads. The heads of all Crotalus
rattlesnakes are about twice as wide as their necks.
Only pit vipers possess this head configuration; coral
snakes do not.
Rattlesnakes belong to the
pit viper family Crotalidae, so named because all
possess visible loreal pits, or lateral heat sensory
organs, between eye and nostril on each side of the head
(Fig. 2). These heat sensory pits are not present in
true vipers, which do not occur in the Western
Hemisphere. The facial pits enable rattlesnakes to seek
out and strike, even in darkness, warm objects such as
small animal prey, as well as larger animals that could
be a threat. The vertically elliptical eye pupils, or
“cat eyes,” are also a characteristic of rattlesnakes
(Fig. 2). Identifying a dead rattler whose rattles are
missing can be done by looking at the snake’s scales on
the underside in the short region between the vent and
the tip of the tail. If the scales are divided down the
center, the snake is harmless. The scales on
rattlesnakes are not divided.
Rattlesnakes come in a
great variety of colors, depending on the species and
stage of molt. Most rattlers are various shades of
brown, tan, yellow, gray, black, chalky white, dull red,
and olive green. Many have diamond, chevron, or blotched
markings on their backs and sides.
Elliptical eye pupil
Fig. 2. Rattlesnake head
showing “cat-eye” elliptical pupil and location of the
large loreal pit, characteristic of pit vipers.
Range and Habitat
Rattlesnakes occur only in
North and South America and range from sea level to
perhaps 11,000 feet (over 3,000 m) in California and
14,000 feet (4,000 m) in Mexico, although they are not
abundant at the higher elevations. They are found
throughout the Great Plains region and most of the
United States, from deserts to dense forests and from
sea level to fairly high mountains. They need good cover
so they can retreat from the sun. Rattlers are common in
rough terrain and wherever rodents are abundant.
Young or small species of
rodents comprise the bulk of the food supply for most
rattlesnakes. Larger rattlers may capture and consume
squirrels, prairie dogs, wood rats, cottontails, and
young jackrabbits. Occasionally, even small carnivores
like weasels and skunks are taken. Ground-nesting birds
and bird eggs can also make up an appreciable amount of
the diet of some rattlers. Lizards are frequently taken
by rattlers, especially in the Southwest. The smaller
species of rattlesnakes and young rattlesnakes regularly
feed on lizards and amphibians.
Rattlesnakes consume about
40% of their own body weight each year. Many prey are
killed but not eaten by rattlesnakes because they are
too large or cannot be tracked after being struck. One
male rattler captured in the field had consumed 123% of
its weight, but young rattlers frequently die due to
lack of food. Domestically raised rattlesnakes will
survive when fed only once a year, but in the field,
snakes usually feed more than once, depending on the
size of prey consumed. A snake may kill several prey,
one after another, and of different species. When
rodents and rabbits are struck, the prey is immediately
released. The snake then uses its tongue to track the
prey to where it has died.
Digestion is quite slow
and usually no bones remain in the feces, called
“scats.” Hair, feathers, and sometimes teeth, however,
can usually be identified in scats. Rattlesnakes use
very little energy except when active, and they probably
are active for less than 10% of their lives. They are
not very active unless food is scarce. They store much
fat in their bodies, which can last them for long
General Biology, Reproduction, and Behavior
When a rattlesnake strikes
its prey or enemy, the paired fangs unfold from the roof
of its mouth. Prior to the completion of the forward
strike motion, the fangs become fully erect at the outer
tip of the upper jaw. The erectile fangs are hollow and
work like hypodermic needles to inject a modified
saliva, the venom, into the prey. Rattlesnakes can
regulate the amount of venom they inject when they
Mature fangs generally are
shed several times a season. They may become embedded in
the prey and may even be swallowed with the prey. When
one mature fang in a pair is lost, it will soon be
replaced by another functional mature fang. A series of
developing fangs are located directly behind one another
in the same sheath at the roof and outer tip of the
mouth (Fig. 3). If a newly replaced fang is artificially
removed, it may require weeks or longer before another
replacement will be fully effective. One fang can
function, however, while the other in the pair is being
replaced. Fangs that get stuck in a person’s boot are
not very dangerous; they cannot contain much venom since
they serve only as a hollow needle. The external opening
of the hollow fang is a groove on the outside of the
fang, set slightly back from the tip to prevent it from
becoming plugged by tissue from the prey (Fig. 3).
Rattlesnakes cannot spit
venom, but the impact of a strike against an object can
squeeze the venom gland, located in the roof of the
mouth, and venom may be squirted. This can happen when a
rattler strikes the end of a stick pointed at it, or the
wire mesh of a snake trap. The venom is released
involuntarily if sufficient pressure is exerted, as
occurs when venom is artificially “milked” from live
snakes. Such venom is dangerous only if it gets into an
open wound. Always wear protective clothing when
Female rattlesnakes are
ovoviviparous. That is, they produce eggs that are
retained, grow, and hatch internally. The young of most
species of rattlesnakes are 6 to 8 inches (15 to 20 cm)
when born. They are born with a single rattle or button,
fangs, and venom. They can strike within minutes, but
being so small, they are not very dangerous. Average
broods consist of 5 to 12 young, but sometimes twice as
many may be produced.
breeding season lasts about 2 months in the spring when
the snakes emerge from hibernation. Sperm is thought to
survive in the female as long as a year. During summer,
pregnant females usually do not feed, so few are ever
captured that contain eggs about to hatch. The young are
born in the fall. Most rattlesnakes are mature in 3
years, but may require more time in northerly areas.
Rattlesnakes may not produce young every year.
The sex of a rattlesnake
is not easy to determine. Even though the tail of the
rattlesnake (the distance between the vent and the
rattles) is quite short, it is much longer in males than
in females of the same size. The paired hemipenises of
male snakes are not visible except during mating, when
one of these paired hollow organs is turned inside out
and extruded from the cloaca. If both are extruded
artificially, they appear like two forked, stumpy legs.
Snakes never close their
eyes, since they have no eyelids. They are deaf, but can
detect vibrations. They have a good sense of smell and
vision, and their forked tongues transport microscopic
particles from the environment to sensory cells in pits
at the roof of the mouth. A rattlesnake uses these pits
to track prey it has struck and to gather information
about its environment.
Snakes have a large number
of ribs and vertebrae with ball-and-socket joints. Each
rib is joined to one of the scales on the snake’s
underside. The snake accomplishes its smooth flowing
glide by hooking the ground with its scales, which are
then given a backward push from the ribs. Rattlesnakes
often look much larger when seen live than after they
have been killed. This happens because their right lung
extends almost the full length of the tubular body, and
when the snakes inhale they can appear much fatter and
more threatening. The expulsion of the air can produce a
Rattlesnakes, like other
snakes, periodically shed their skin. When the new skin
underneath is formed, the snake rubs its snout against a
stone, twig, or rough surface until a hole is worn
through. After it works its head free, the snake
contracts its muscles rhythmically, pushing, pulling,
and rubbing, until it can crawl out of the old skin,
which peels off like an inverted stocking. Each molt
produces a new rattle. Some rattles usually break off
from older snakes. Even if no rattles have been lost,
they do not indicate exact age because several rattles
may be produced in one season.
Even though the optimum
temperature for rattlesnakes is around 77o to 89o F (25o
to 32o C), the greatest period of activity is spring,
when they come out of hibernation and are seeking food.
If lizards are active, be alert for rattlesnakes. The
activity period for rattlers can vary from about 10
months or so in warm southern regions to perhaps less
than 5 months in the north and at high elevations.
Depending upon availability of good, dry denning sites
below the frost line, rattlesnakes may hibernate alone
or in small numbers. However, sometimes they den in
large groups of several hundred in abandoned prairie dog
burrows or rock caverns, where they lie torpid in groups
or “balls.” All dens must be deep enough so the
temperature is not affected by occasional warm days. If
not, the snakes might emerge too early in spring only to
become sluggish and vulnerable should the weather again
turn cold. Since snakes are cold-blooded animals and
their body temperature is altered by air temperature,
refrigeration makes them sluggish and easy to handle for
Rattlesnakes usually see
humans before humans see them, or they detect soil
vibrations made by walking. They coil for protection,
but they can strike only from a third to a half of their
body length. Rattlers rely on surprise to strike prey.
Once a prey has been struck, but not killed, it is
unlikely that it will be struck again. Experienced
rodents and dogs can evade rattlesnake strikes.
Rattlesnakes may appear
quite aggressive if exposed to warm sunshine. Since they
have no effective cooling mechanism, they may die from
heat stroke if kept in the sun on a hot day much longer
than 15 or 20 minutes.
If a rattlesnake has just
been killed by cutting off its head, it can still bare
its fangs and bite. The heat sensory pits will still be
functioning, and the warmth of a hand will activate the
striking reflex. The head cannot strike, but it can bite
and inflict venom. The reflex no longer exists after a
few minutes, or as long as an hour or more if it is
cool, as rigor mortis sets in.
Damage and Damage Identification
The greatest danger to
humans from rattlesnakes is that small children may be
struck while rolling and tumbling in the grass. Only
about 1,000 people are bitten and less than a dozen
people die from rattlesnake venom each year in the
United States. Nevertheless, it is a most unpleasant
experience to be struck. The venom, a toxic enzyme
synthesized in the snake’s venom glands, causes tissue
damage, as it tends to quickly tenderize its prey. When
known to be abundant, rattlesnakes detract from the
enjoyment of outdoor activities. The human fear of
rattlesnakes is much greater than the hazard, however,
and many harmless snakes inadvertently get killed as a
result. Death from a rattlesnake bite is rare and the
chance of being bitten in the field is extremely small.
operators and farmers usually can identify rattlesnake
bites on people or on livestock without much difficulty,
even if they did not witness the strike. A rattlesnake
bite results in almost immediate swelling, darkening of
tissue to a dark blue-black color, a tingling sensation,
and nausea. Bites will also reveal two fang marks in
addition to other teeth marks (all snakes have teeth;
only pit vipers have fangs too). Rattlesnakes often bite
livestock on the nose or head as the animals attempt to
investigate them. Sheep, in particular, may crowd
together in shaded areas near water during midday. As a
consequence, they also frequently are bitten on the legs
or lower body when pushed close to snakes. Fang marks
and tissue discoloration that follows in the major blood
vessels from the bite area are usually apparent on
livestock that are bitten (see Wade and Bowns 1982,
pages 32 and 34 in the Damage Identification section of
Most species of
rattlesnakes are not considered threatened or
endangered. Since they are potentially dangerous, there
has not been much support for protecting them except in
national parks and preserves. However, since there are
state and local restrictions, contact local wildlife
agencies for more information.
Damage Prevention and Control Methods
An occasional single
poisonous snake can be destroyed if one has enough
determination. In areas where the habitat is favorable
for rattlesnakes, copperheads, or water moccasins, a
significant reduction in their population density may be
difficult. In snake country, most people learn to “keep
their eyes open” and be cautious.
When feasible, the most
effective way for a homeowner to protect a child’s play
area from rattlesnakes is to construct a
rattlesnake-proof fence around it. The fencing must be
tight. If wire mesh is used, it should be 1/4-inch
(0.6-cm) mesh and about 3 feet (1 m) high. Bury the
bottom 3 or 4 inches (8 or 10 cm) or bend outward 3 or
more inches of the base of the wire to discourage other
animals from digging under the fence. Put the stakes on
the inside and install a gate that is tight-fitting at
the sides and bottom, equipped with a self-closing
spring. The benefit of the fence will be lost if wood,
junk, or thick vegetation accumulates against the
outside of the fence. Vegetation that has ground-level
foliage also provides attractive hiding places for
rattlesnakes, so it should be removed or properly
pruned. Tight-fitting doors will prevent snakes from
entering outbuildings. The foundations of all buildings
should be sealed or tightly screened with 1/4-inch
(0.6-cm) wire mesh to keep out snakes.
It is always desirable to
use nonlethal biological means of control when feasible.
Although good quantified data are not available to
evaluate the effectiveness of removing the prey of
snakes, effective, sustained rodent control will reduce
the attractiveness of a rural residence or other
facility to rattlesnakes. Snakes will not remain in
habitat made less favorable for them. Hiding places
under buildings, piles of debris, or dense vegetation
should be removed. Hay barns and feed storage areas that
encourage rodents will attract rattlers.
No methods are known that will frighten
rattlesnakes. Sounds certainly will not work because
snakes are deaf.
Many potential snake
repellents have been researched, only to be found
ineffective. All species of snakes are likely to cross a
strip of repellent substance if they want to get to the
other side. Dr. T’s Snake-A-Way®, a mixture of sulphur-naphthalene,
has been registered by EPA; however, its registration in
California was denied as of July 1991, because required
data was not submitted. A Y-shaped laboratory enclosure
that provided rattlers with a choice of crawling into a
tunnel with odor or one free of odor showed they usually
chose the passage free of odor. No field test data is
available. To be of practical use, the odor of a snake
repellent must not be too objectionable to people.
Toxicants No effective
toxicant is registered for the control of rattlesnakes.
When rodents were poisoned with various rodenticides and
then fed to rattlesnakes, the snakes were not affected.
Apparently, digestion is too slow for the toxicants to
have an effect on snakes.
It may be possible to kill
rattlesnakes in burrows and rock dens with toxic gas,
although this is not a very practical method. Calcium
cyanide is a chemical frequently recommended, but no
lethal gas has had good success because snakes have such
a slow rate of metabolism, especially when in
hibernation. In addition, susceptible nontarget species
in the burrows or dens may become victims. In the spring
and early summer, when hibernating snakes are about to
emerge, gasoline poured down a burrow or into a den will
drive the snakes out. As the snakes exit they can be
clubbed, shot, or captured alive with snake tongs that
secure a snake at its neck. If transported in a bag, tie
the top securely. Many snake hunters push a hose down a
burrow and after listening to confirm that rattlesnakes
are present, pour 1 to 2 ounces (30 to 60 ml) of
gasoline into a funnel on the hose and then blow on the
hose. This technique seems quite effective for
seasonally reducing rattlesnake numbers, but it may be
lethal to nontarget animals including nonpoisonous and
beneficial snakes. To be effective, community- wide
campaigns should extend over several days, since many
snakes may escape into holes or crevices. Snake hunters
should wear protective clothing such as pants, heavy
gloves, and boots.
Various combinations of
fencing and traps at known rattlesnake dens can be very
successful if one is trying to collect rattlesnakes,
because in some localities several hundred rattlesnakes
may occupy the same den. If all but one opening can be
blocked, it is then quite simple to pipe or otherwise
channel the emerging rattlesnakes into a large oil drum
or other receptacle. If it is not possible to find all
den openings, inward-sloping drift fences of 1/4-inch
(0.6-cm) hardware cloth mesh, 1 or 2 feet (0.5 m) high,
with fish-type funnel traps (Fig. 4) will suffice. The
inward sloping funnel makes it difficult for the snakes
to escape. If a wooden nestbox is attached to one side
of these traps, the snakes will usually hide in the box
and not spend as much time trying to escape. Drift-fence
funnel traps also catch many other animals. Therefore,
this control method requires daily inspection and
usually is not very practical except at dens. Glue
boards are useful for trapping rattlesnakes that are in
or under buildings (Knight 1986). To trap rattlesnakes,
use a plywood board approximately 24 x 16 inches (61 x
41 cm). Securely tack a 6 x 12-inch (15 x 30-cm) rodent
glue trap (or use bulk glue to make a similar-sized glue
patch) to the plywood (Fig. 5). Place the board against
a wall, as this is where snakes are likely to travel.
The rattlesnake will become stuck while attempting to
cross the board. Do not place the board near any objects
(pipes, beams) that the snake can use for leverage in
attempting to free itself.
Fig. 5. A glue trap to
catch rattlesnakes can be made by attaching three to six
rodent glue traps to a wooden board.
The glue trap can be
removed easily using a long stick or pole with a hook or
by an attached rope if a hole is drilled through the
plywood board. Animals trapped in the glue can be
removed with the aid of vegetable oil, which counteracts
Do not use glue boards
outdoors or in any location where they are likely to
catch pets or desirable nontarget wildlife. The glue can
be quite messy and is difficult to remove from animals.
A shotgun has often been
used to eliminate individual rattlesnakes around a rural
homestead. Similarly, a pistol loaded with birdshot is
very effective at close range. Shooting is not
considered effective for reducing large populations.
Dynamite blasting of known
dens is dangerous and has questionable advantages. There
is no way to know what kinds and how many snakes have
been killed, and the blast may create an even better den
for future rattlesnakes.
Rattlesnakes have natural
predators, but the predators are not likely to help much
in controlling rattlesnake populations. Some dogs,
especially if they have experienced a snake bite, become
excellent guards for children. They will bark when a
snake is discovered, and many can kill rattlesnakes as
well. Domestic geese and turkeys may also help, by
acting as an alarm and by frightening snakes. Hogs do
not provide practical protection around a homestead.
The best protection for
humans when traveling in snake country is common sense
in choosing protective foot and leg wear. When climbing,
one should beware of putting a hand up over rocks.
Rattlesnakes might be waiting there for a rodent, and
the warmth in a hand may cause the snake to strike
reflexively. Care should be taken at night, when snakes
are more active, and the chance of stepping on a snake
is greater. Fortunately, rattlesnakes try to avoid
The best first aid for a
poisonous snake bite is to seek immediate medical care
and to keep the victim calm, warm, and reassured. Do not
drink alcohol or use ice, cold packs, or freon spray to
treat the snake bite or cut the wound, as was once
If a victim of snake bite
is several hours from a car and medical aid, apply a
light constricting cloth or other band on the bitten
limb, 2 to 4 inches(5 to 10 cm) from the bite and
between bite and heart. Make sure it is not as tight as
a tourniquet. It should be easy to insert a finger under
the band. Loosen it if swelling occurs. Apply suction at
the wound for at least 3/4 of an hour by mouth (if no
mouth sores), or with a snake bite kit, but again, only
if medical assistance is several hours away.
The causes of human death
from rattlesnake venom are varied, but usually occur
from extended hypotension and cardiopulmonary arrest.
Usually within a few minutes after being struck the
victim will experience pain and swelling at the wound
Economics of Damage and Control
The greatest economic loss
to humans from rattlesnakes comes from the number of
domestic livestock and pets that are killed. Horses and
cattle are most frequently struck in the head while
grazing. Some have claimed that rattlesnakes benefit
ranchers by the number of rodents they eat, but current
predator-prey theory discounts this. It is very doubtful
that snakes have much effect on the density of rodents.
The commercial value of
rattlesnakes consists of the venom, rattles, skins and,
to a limited degree, the meat.
Figures 1 through 3 by
Emily Oseas Routman.
Figures 4 and 5 by Jill
For Additional Information
Dunkle, T. 1981. A perfect
serpent. Science 81 2:30-35.
Duvall, D., M. B. King,
and K. J. Gutzwiller. 1985. Behavioral ecology and
ethology of the prairie rattlesnake. Natl. Geogr. Res.
Dolbeer, R. A., N. R.
Holler, and D. W. Hawthorne. 1994. Identification and
control of wildlife damage. Pages 474-506 in T. A.
Bookhout ed. Research and management techniques for
wildlife and habitats. The Wildl. Soc. Bethesda,
Kilmon, J., and H.
Shelton. 1981. Rattlesnakes in America. Shelton Press,
Sweetwater, Texas. 234 pp.
Klauber, L. M. 1972.
Rattlesnakes: their habits, life histories, and
influence on mankind, 2 vols. Univ. California Press,
Berkeley. 1533 pp.
Klauber, L. M. 1982.
Rattlesnakes: their habitats, life histories, and
influence on mankind. Abridged by K. H. McClung. Univ.
California Press, Berkeley. 350 pp.
Knight, J. E. 1986. A
humane method for removing snakes from dwellings. Wildl.
Soc. Bull. 14:301-303.
Marsh, R. E., and W. E.
Howard. 1982. Vertebrate pests. Pages 791-861 in A.
Maillis, ed. Handbook of pest control, 6th ed. Franzak
and Foster Co., Cleveland, Ohio. 1001 pp.
Pinney, R. 1981. The snake
book. Doubleday & Co., New York. 248 pp.
San Julian, G. J., and D.
K. Woodward. 1986. What you wanted to know about all you
ever heard concerning snake repellents. Proc. Eastern
Wildl. Damage Control Conf. 2:243-248.
Seigle, R. A., J. T.
Collins, and S. S. Novak. 1987. Snakes: ecology and
evolutionary biology. Macmillan Publ. Co., New York. 529
Story, K. 1987. Snakes:
separating fact from fantasy. Pest Control Technol.
Wade, D. A., and J. E.
Bowns. 1982. Procedures for evaluating predation on
livestock and wildlife. Bull. No. B-1429, Texas A & M
Univ., College Station. 42 pp.
Scott E. Hygnstrom Robert
M. Timm Gary E. Larson
PREVENTION AND CONTROL OF
WILDLIFE DAMAGE — 1994
Division Institute of Agriculture and Natural Resources
University of Nebraska -Lincoln
United States Department
of Agriculture Animal and Plant Health Inspection
Service Animal Damage Control
Great Plains Agricultural
Council Wildlife Committe