Amphibians and Reptiles of Minnesota

A Complete On-line Field Guide to Minnesota's Amphibians and Reptiles

Timber Rattlesnake - Crotalus horridus (Venomous) PDF Print E-mail
Snakes of Minnesota - Snakes of Minnesota



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Timber rattlesnake, Crotalus horridus, from Fillmore County, MN

 

 

 

 

 

 

 

 

Status

Because of serious decline in this species, the timber rattlesnake is listed
as a Threatened species and Species in Greatest Conservation Need in Minnesota.


Description

This is a large, venomous Minnesota species that is very heavy bodied and
measures from 36 to 60 inches in length; the record is 74 1/2 inches
(Conant and Collins, 1991). Timber rattlesnakes have a diamond shaped head
which is set off from their relatively thin neck. The pupils of the eyes
are elliptical in bright light and there is a heat-sensitive pit between the
eye and nostril on both sides of the head.
Ground color may be variable, but a banded pattern is almost always
present. Ground color may be yellow, with or without a rusty orange stripe
down the center of the back, or gray or brown. There are black bands (usually not
spots) that run across the back for the entire length of the snake. These
bands are from 2 to 4 scales wide with a space of about 4 to 6 scales
between them and have a light border. The belly is usually the same color as
the dorsal ground color and unmarked, except for some darker stippling on
some specimens. The tail is solid black above and below with a tan rattle
at the end. The scales are keeled and anal plate is single. The subcaudals
are single instead of divided as in all harmless Minnesota snakes. Young
are patterned the same as the adults and are gray until their first shed.
They are 10 to 13 inches in length at birth (Johnson, 1992).


Subspecies

None. There was a recognized subspecies of timber rattlesnake, the canebrake
rattlesnake, Crotalus horridus atricaudatus, until the 1970's when it was
found that the definitive characteristics were shared by both subspecies.
The timber rattlesnake is now considered a single species. Even so, the
canebrake was a southern subspecies, and its range did not include
Minnesota.

Range

This species is found throughout most of the southeastern United States
and ranges northward from Iowa into Minnesota and Wisconsin via a
narrow band along the Mississippi River. In Minnesota, they are recorded
from eight southeastern counties, but only six of these may hold breeding
populations at this time (Oldfield and Moriarty, 1994). It does not appear
that any new records for this snake will turn up although there are rumors
of rattlers around Mankato (Breckenridge, 1944 and Tom Jessen, pers.
comm.). There is suitable timber habitat in that region; however, it is likely
that such rumors are the result of encounters with western fox snakes; large,
harmless Minnesota snakes that are very common in that area. In fact, some
of the existing records may unfortunately become invalid due to habitat
loss and human interference, activities to which timber rattlesnakes
seem particularly sensitive.


Habitat

Timber rattlesnakes live in the same habitat as milk snakes and prairie
ringneck snakes in Minnesota, steep bluffs with rocky outcroppings. These
snakes favor south and southwest sides of the bluffs and spend most of
their time in the sunny open areas surrounded by forest. They overwinter in
dens that travel into the sides of the bluff. They overwinter communally
with other timber rattlesnakes and also other species of snakes such as
bullsnakes, milk snakes, eastern racers, and, less commonly,
garter, brown, redbelly, and ringneck snakes.


Habits

Timber rattlesnakes are among the last snakes to emerge from
hibernation in the spring, and among the first to retire to their winter
retreats in the fall. They may bask around their den openings in late April or
early May, but they do not move away from their dens until late May. Many
individuals move to other small, sunny openings of the bluff to spend
their summer. Others, particularly males, may travel some distance from the
den sites (a few miles) deeper into the surrounding forest or into the
lowland meadows and farmland. Still others may spend the entire summer
near the den site, especially the gravid females. In the spring and fall,
timber rattlesnakes are active during the day, and during the hot summer
months, they become nocturnal.

Timbers appear to be lie and wait predators using many senses to detect
prey. They have been observed to lie coiled up next to a fallen log with
their head resting on the log. The log acts as a runway for rodents. As a
rodent approaches, vibrations traveling through the log alert the snake of a
possible meal. Eyesight and the heat sensitive pits direct the strike
(Oldfield and Moriarty, 1994).

Timber rattlesnakes are surprisingly calm when encountered in the wild.
Many will sit motionless hoping that you will not see it. If you do
approach too closely, it may slither under a rock or into a crevice without
rattling, unlike some other species of rattlesnakes which are more apt to
stand their ground. Most of the specimens that I have found failed to
sound their rattle, even when seriously molested, and did not attempt to
bite. When rattlesnakes do rattle, they elevate the rattle and tail high in the
air making it obvious. Nonvenomous snakes which vibrate their tails and
produce a similar sound, will hold their tails close to the ground.

The rattle is comprised of a series of horn-like segments that are loosely
attached to one another. When the tail is vibrated, these segments strike
against one another to produce a buzzing sound. When a baby timber is
born it has a prebutton on the end of its tail. With the first shed, the
prebutton is lost and it is replaced by the first segment. Each time the
snakes sheds thereafter, another segment is added, producing the rattle.
Because the snake receives a new segment with every shed, one cannot
determine the snakes age by the length of its rattle. The rattle is also
fragile and it is not uncommon for the snake to have a few of the last
segments broken off, to be replaced with more.

Timber rattlesnakes breed in the spring or fall (July or August) and are
sexually mature in 7 to 12 years of age. Males may "combat" with other
males. The two snakes intertwine the posterior portion of their bodies
together while they raise the anterior half into the air and try to push each
other to the ground. The successful male will go on to breed with a female.
The females may breed every 2 to 4 years (3 is the most common
interval) and may spend their gestation period near the overwintering dens.
They do not eat during this period, but they spend much of their time basking.
They are ovoviviparous and give birth to about a half dozen young inside
individual membranes. The young are born in August or September and are
10 to 13 inches in length.


Food

Timber rattlesnakes prey upon small mammals. Mice, chipmunks, ground
squirrels, voles, shrews, and squirrels comprise the majority of this
snake's diet. Birds and birds' eggs (primarily ground nesters) are consumed at times.


Snakebite

Timber rattlesnakes should be protected as part of our natural
ecosystem. People building new homes in rattlesnake territory are concerned
that these snakes will invade their homes and yards. Before these people
arrived, it was the rattlers' home and "yard". It really still is and should be.
The last fatality from a timber rattlesnake bite in Minnesota was in the
1800's! These snakes are not aggressive and all but a very small number of
bites can be avoided. Use common sense. Be careful where you sit, step,
or place your hands. If you are hiking in rattlesnake territory, wear hiking
boots. If you are lucky enough to see a rattler, observe it then walk away
from it. The snake will not chase you or even follow you. Guaranteed. They                                                                                            will just try to escape when they think it is safe to do so. I
am not going to go into the treatment of a rattlesnake bite; there are
many other sources for that.

Why Protect Timber Rattlesnakes?

Timber rattlesnakes are declining in much of their natural range. They are
offered protection in most of the states where they occur. The following
are reasons for their elevated status in Minnesota, but they apply
throughout the timbers' range. Habitat destruction is one reason these
snakes have declined. They simply cannot adjust to live in another habitat
type.

Bounties were paid for rattlesnakes in several southeastern Minnesota
counties. The bounty was lifted in 1987, but by then many dens were
destroyed. Unlike most of Minnesota's snake species, timber rattlesnakes
cannot recuperate as quickly from unnatural losses. First, they are found in a
specific habitat that is only found in a very small part of Minnesota. High
up in the bluffland as far away from people as you can get. Second, on
average, timber rattlers do not mature until they are 9 or 10 years of age.
This is far older than any of our other snake species. When they do
reproduce, they have relatively small litters. Additionally, females only
reproduce, on average, every two or three years. Third, for those young snakes
fortunate enough to make it to adulthood, they may have a long lifespan. This
indicates that adult timbers are not easily replaced. This is how nature
limits these snakes. An area will not be overrun with rattlesnakes if it is
preserved. Nature will limit these snakes.


Some people may want to remove rattlesnakes from their property and
relocate them to another area with another population. I am glad to see a
proposed solution that is not fatal to the snakes. Unfortunately, at this
time, relocations of adult timber rattlesnakes (even to existing
populations) seemingly do not work. The relocated adults appear to wander aimlessly, do not
feed, and fail to recognize known den sites (Reinert and Rupert, 1996). The
snakes could not properly overwinter and they froze. It is probable that favorable
results would be met using neonate snakes. It is assumed that this would be
a better approach (Reinert and Zappalorti, 1998).

The best solution (for now) is to leave the snakes be. It is possible to live
together with these snakes.

 
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