|
Black Rat Snake
Elaphe obsoleta obsoleta
 
Status
The Black Rat Snake is listed as a species
of Special Concern by the State of Minnesota.
Description
Black Rat Snakes are among the largest
of Minnesota's snakes. Adults range from 40 to 74
inches in length. The record is 101 inches (Conant and Collins,
1991). It is non venomous and,
as its name implies, is generally a black snake, although
very few specimens are completely
pitch black. Most adults have shiny, unmarked black heads
and necks with bright white labials.
Dorsally, the bodies are black or brown with white, yellow,
or red in between the scales and on
the scale tips as well. In most cases these highlights accent
a blotched pattern that is much
more evident in young specimens. Posteriorly, the snake becomes
solid black again. Ventrally,
the throat and neck are white. At the middle, black or brown
invades the white and posteriorly
the ventrals are a shiny bluish black. The anal plate is divided
and the scales are weakly
keeled dorsally becoming smooth on the last two or three scale
rows on the sides. The
young are brightly patterned with black or dark brown blotches
on the back and sides on a
white or light gray background. This pattern fades quickly
and it will reach adult coloration in
about two or three years. Young are about 11 to 13 inches
at birth.
Subspecies
Elaphe obsoleta contains about five subspecies.
Only one, the Black Rat Snake (Elaphe
obsoleta obsoleta), occurs in Minnesota.
Range
This subspecies has a very broad range
throughout Eastern North America, from southeastern
Minnesota to northern Louisiana and east to the eastern seaboard.
In Minnesota, this snake
has a very small range. Only a few southeastern counties (Olmstead,
Fillmore, and Houston)
have documented records and less than five individuals have
been recorded for the state until
recently when a den site was identified. The numbers are still
relatively low. I have found Black
Rat Snakes in the southern portion of Allamakee county, Iowa,
the next county south of Houston County, Minnesota. Their
habits and habitat in Minnesota make them a rather
difficult snake to locate outside of hibernation aggregations.
Habitat
Black Rat Snakes prefer heavily wooded
habitats. They are one of the few Minnesota snakes
that are actually found in deep woodland areas. They are found
on the north and east sides of
bluffs while other snake species prefer the other side of
the bluff.
Habits
Black Rat Snakes emerge from their
rocky crevice retreats in late April or early May. They
hibernate with other Rat Snakes and/or with many other snakes
species, most notably
Timber rattlesnakes, Racers, and Bullsnakes. Many of them
move to the other side of the
bluff, but individuals may be scattered among the entire bluff.
They are diurnal even during
hot weather, though they do move at night on occasion.
These snakes are difficult to find
in their wooded habitat. Farther west, they frequent more
flat open meadows and grassland where they use cover, so one
may flip tin, boards, and
rocks and turn up many of these snakes. In Minnesota, western
Wisconsin, and north-
eastern Iowa, they do not use that cover nearly as much. Instead
they climb trees up to
40 feet high and may spend days hiding in the hollows of trees.
When approached, Black
Rats usually remain motionless. With their cryptic black coloration,
they become invisible
against the bark or resting on the dark forest floor. A few
Black Rat Snakes are found under
rocks along bluff outcroppings or roadcuts, but to search
for these snakes in their vast
forest habitat, I rely more heavily upon road cruising at
night on hot, humid nights just
before or just after a storm (LeClere, 1996). There may be
more Rat snakes in Minnesota
than it appears, because this snake spends most of its time
in areas where other snake
species are not, so many herpers do not look in places these
snakes are found.
When caught, most Black Rat snakes
will bite, although most will calm down readily.
Still, some are nervous and will thrash and strike even in
captivity. They will vibrate their
tails which produces a rattling sound causing it to be slain
as a rattlesnake by farmers
and locals. Some will kill it simply because they are startled
by a 5 or 6 foot black snake.
These snakes breed in the spring
and the female deposits about 15 eggs in rotting wood
in late summer. In the fall, the eggs hatch. Black Rat Snakes
usually migrate back to
their hibernation dens in October.
Food
The adults usually consume rodents. Mice,
chipmunks, voles, shrews, even full grown
squirrels have been reported in its diet. These snakes probably
prey on birds and birds's
eggs most heavily of all Minnesota snakes because of their
climbing ability and time
spent in trees. The young will feed on frogs, especially treefrogs,
lizards and young mice.
A juvenile Black Rat I caught on the road just before a storm
had eaten a Gray treefrog,
Hyla ssp., (LeClere, 1996).
|
