| Avoiding Wildlife Problems  Managing
Rattlesnake Problems
Walter E. Howard
Professor Emeritus of Wildlife Biology and Vertebrate Ecology
Department of Wildlife, Fisheries and Conservation Biology
University of California
Davis, California 95616
Introduction Rattlesnakes 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.
Fig. 1. Prairie rattlesnake,
Crotalus viridis viridis
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. oreganus).
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.
Damage Prevention and
Control Methods*
Exclusion -- Construct
a snake-proof fence around areas of human activity.
Seal entrances to buildings and structures.
Habitat Modification -- Eliminate
shelter for snakes.
Control rodents; they attract snakes. Repellents -- None
are available. Toxicants -- None
are available. Fumigants -- Generally
not effective in dens. Trapping -- Effective
in some situations when properly placed. Glue boards are useful
in removing rattlesnakes from buildings. Shooting -- Effective
where safe. Other Methods -- Organized
snake hunts may be successful in spring or early summer. Snake Bite -- Wear
protective clothing and be careful when climbing and walking.
If a bite occurs, keep the victim calm, warm, and reassured. Seek medical
attention immediately. *Information pertains to other poisonous
snakes.
Identification
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. Rattlesnake head showing "cat-eye" elliptical
pupil and location of large loreal pit, characteristic of pit vipers.
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. 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.
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.
Food Habits
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 periods.
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 strike.
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).
Fig. 3. Head of a rattlesnake
in striking position. Supplementary fangs are covered by a sheath of tissue.
Each fang is located in a double socket. Replacement fangs appear in what
are currently empty sockets.
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 handling rattlesnakes.
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.
The 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 raffles) 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 hiss. 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 77 to
89 degrees F (25 to 32 degrees 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 coldblooded
animals and their body temperature is altered by air temperature, refrigeration
makes them sluggish and easy to handle for displaying. 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.
Experienced livestock 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 this book).
Legal Status
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.
Exclusion 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.
Habitat Modification
It is always desirable to use non-lethal 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.
Frightening
No methods are known that will frighten rattlesnakes. Sounds certainly
will not work because snakes are deaf. Repellents
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 (registered trademark), 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.
Fumigants
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.
Trapping
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.
Fig. 4. A fish-type funnel trap
of 1/4-inch hardware cloth attached to an inward-sloping drift fence of
the same wire mesh can be useful in trapping snakes as they emerge from
a multi-opening den. Escape will be reduced if a wooden nest box is attached
to the funnel trap.
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 object (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 the adhesive.
Do not use glue boards outdoors or in any location where they are likely
to catch pets or desirable non-target wildlife. The glue can be quite messy
and is difficult to remove from animals.
Shooting
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.
Other Methods
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. Snake Bite 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 people. 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 recommended.
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 snakebite
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 site.
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.
Acknowledgements
Figures 1 through 3 by Emily Oseas Routman.
Figures 4 and 5 by Jill Sack Johnson. 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. 1:80-111.
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,
Maryland. 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 pp. Story, K. 1987. Snakes: separating fact from
fantasy. Pest Control Technol. 15(11):54,55,58,60. 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.
Editors Scott E. Hygnstrom
Robert M. Timm
Gary E. Larson |
