Реферат: SNAKES Essay Research Paper
SNAKES Essay, Research Paper
Have you ever wondered exactly what a snake is?
Snakes are elongated, limbless reptiles that have often appeared in
art and mythology. Scientists have currently discovered an estimated
2,500-3,000 living species of snakes living throughout the world except in
the arctic regions. There is one exception to the old world viper, which has
been found as far north as Scandinavia (60? North Latitude).
The size variation of snakes ranges from slender blind snakes
(family Leptotyphlopidae) which reaches a maximum length of 13cm
(5 in.), to the largest snake on record, the Asiatic reticulated python,
which attained a record length of 10m (33 ft).
Have you ever asked anyone what the phyical characteristics of a
snake is? To answer your question: Snakes lack limbs, a sternum (breast
bone), shoulder girdle, exterior ear openings, and urinary bladder, and
most snakes (but not all) lack a pelvic girdle.
There are two types of snakes: constrictors and poisonous.
Constrictors will either stalk their prey or lay very still until Its prey come
near it. It will then strike forward and wrap around the prey crushing it and
cutting off all air supply. The initial strike takes less than one-half second.
It will then swallow the prey animal head first because the hair of animals
folds backwards and makes it easier to swallow.
Poisonous snakes inject a very potent venom into their prey
Keith 2through fangs. There are three different class of venomous snakes:
Opisthoglyphus (rear fanged), Proteroglyph (front fanged, with holes
pointing outward for “spraying”) and Solenoglyph (front fanged and
carved). The most common of these three are Solenoglyphs, which have
fangs that can be folded along the roof of the mouth.
All snakes have powerful digestive enzymes to breakdown the
hair, bones, and other parts of their preys’ body. As part of the digestive
system the salivary glands also produce powerful enzymes. If saliva
containing these enzymes enters the wounds of a prey animal, it not only
starts the digestive process, but also may cause such serous tissue damage
that the prey dies.
The destructive substances in a snakes venom include neurotoxins
and hemotoxins. Neurotoxins paralyze the central nervous system and
cause heart and respiratory failure; hemotoxins destroy blood vessels and
blood cells and cause internal hemorragins. The different substances are
not uniformly present in all snake venom, but vary with the species and
the individual snakes within a species. Venom retains digestive powers;
injected into a prey animal it may shorten the usual days-long digestive
process of a snake by more than half.
Less than one-third of the 2,500-3,000 living species of snakes are
classified as venomous, and less than 300 species are fatal to humans. In
the United States, more than twice as many people are killed by bees,
wasps, and scorpion stings as by snake bites.
Keith 3There are four basic kinds of snake movement: Lateral (horizontal)
undulation, conceltina movement sidewinding and rectilinear. Lateral
undulating, also called serpentine movement is the most common form
and is used by all snakes. By alternately contracting and relaxing muscles
down each side of the body, the snake forms itself into a number of
rearward-moving horizontal waves. While doing so, the snake maneuvers
its body so that the rear of each backward moving wave pushes against
In concertania movement, also called earthworm movement, the
snake anchors the forepart of its body and pulls the rest of its body behind
it in the form of hoizontal curves; it then extends out the forepart of its
body, anchors it, and repeats the process.
Sidewinding is employed on soft sand or other surfaces that offer
no resistance or slip. In sidewinding the snake loops its body into an
S-shape, with only two points of its body coming in contact with the
surface of the ground. It then progressively shifts the two contact points
back along the body consequently propelling its body forward.
Rectilinear, or caterpillar, movement involves a sliding of the skin
back and forth over the body musculature and is therefor possible only in
those kinds of snakes, such as rattlesnakes and boas, which do not have
the skin tightly attached to the underlying musculature. The ribs remain
essentially motionless, and the scales only provide body-to-ground
Keith 4 The vast majority of snakes lay eggs, but in some, the eggs are
retained in the female until hatched, and the young are born live.
Pythons have laid over 100 eggs in a single clutch, and some live bearing
snakes are remarkably prolific. The number of eggs or young is dependant
on the species and how large or small the mother is. No true parental care
of young is known, but a few snakes brood their eggs until they hatch.
Gestation and incubation periods vary according to the species and
temperature. Young snakes escape the eggs by splitting the shell with a
special structure, the egg tooth, which falls off soon after. The life span of
a snake is dependant on the species.APPENDIX 1
COMMON BELIEFS ABOUT SNAKES
1.Snakes are not slimy. They feel more like shoe leather.
2.Snakes are not mean. Most snakes are shy, timid animals.
3.Snakes do not chase people
4.Snakes do not stalk humans.
5.Snakes are not fast. The fastest snake, the Coachwhip, can go about as
fast as the average person can run (7 m.p.h.)
Size. Snakes are almost always described as larger than they really are.
Stories about New England water snakes eight and ten feet long are simply
not true. Northern water snakes rarely exceed three and a half feet in
length, with the largest stretching only four and a half feet. While the
black rat snake, U.S.A’s largest native snake, can reach lengths of just over
eight feet, most New England snakes are less than three feet long.
Poisonous Snakes. The regularity with which people kill a snake first and
ask questions later might lead you to believe that the world is overrun with
poisonous snakes. In fact, venomous snakes only make up about one-third
of the 2,500-3,000 snake species worldwide, and in Massachusetts only
two of the state’s fourteen species of snakes are poisonous (timber
rattlesnake and northern copperhead). Both are rare, reclusive and
generally confined to isolated areas.
Folk Tales. Folk tales about snakes are handed down from generation to
generation and include such things as snakes that charm prey, swallow
their young for protection, poison people with their breath, roll like hoops,
and suck milk from cows. These folk tales could be just interesting and
amusing stories except that many people still believe them. As we learn
more about the true nature of snakes, we can begin to base our perceptions
of them on fact rather than fiction.
APPENDIX 2 CONT.
Myth: When frightened, hoop snakes will bite their tails and roll downhill
like a wagon wheel.
Reality: Anatomically, snakes are not well equipped for rolling and there
are no reliable accounts of this ever occurring. The hoop snake myth may
have been associated originally with mud snakes found in the southern
United States. Mud snakes will occasionally lie in a loose coil shaped like
a hoop, but they slither away from danger like other snakes.
Myth: When confronted with danger, mother snakes swallow their young,
spitting them out later once danger has passed.
Reality: Parental care is not very well developed in snakes and there is no
evidence that mother snakes protect their young in this way. The myth
may result from the fact that some snakes eat young snakes of their own
species or of other species, though usually not their own brood.
Myth: Snakes have the ability to charm prey, especially birds, so they
Reality: There is no evidence that snakes charm their prey. Small animals
may become “frozen with fear” when confronted by snakes but they are
not charmed. Birds may flutter about in front of a snake in an attempt to
lure it away from their nests; occasionally a bird may actually be captured
by the snake, giving the impression that it was charmed. The fact thatAPPENDIX 2 CONT.
snakes never blink may also have played a role in this myth’s origin.
Myth: Milk snakes are so named because of their ability to suck milk
directly from the udders of cows.
Reality: Although milk snakes are common around barns that house cows,
they completely lack the anatomy necessary to suck milk (or anything else
for that matter). Barns are attractive to milk snakes because they provide
abundant food in the form of small rats and mice.
Myth: Puff adders (hognose snakes) mix poison with their breath and can
kill a person at a distance of twenty-five feet.
Reality: Although the bite of a hognose snake can produce swelling and a
burning sensation, these snakes rarely bite people and are not considered
poisonous. When confronted, they do puff themselves up and hiss, but
their breath is harmless.
Cottonmouths in New England
Myth: Swimmers in New England are advised to watch out for poisonous
cottonmouths, also known as water moccasins.
Reality: Simply put, there are no water moccasins in New England. The
cottonmouth, or water moccasin, is a poisonous snake of the southeastern
United States that occurs no farther north than the Great Dismal Swamp of
Virginia. Many people mistake nonpoisonous water snakes for water moccasins.