What is a Snake? A Simple Plan
All snakes have a simple form—a head, long body, and tail. A snake is
really just a tube of bone and muscle wrapped around internal organs. The
relationship between muscles, ribs, and vertebrae give the body incredible
strength and flexibility. Body shapes and lengths of snakes vary. Some
ground dwelling snakes tend to have thick, short bodies with obvious tails.
Tree snakes tend to be long, thin, and very light—much better for climbing
trees! The shortest species known is the thread snake from the West Indies,
only three inches long fully grown. The longest species is the reticulated
python from Southeast Asia, which can grow up to 32 feet in length.
They're So Cool. Snakes are "cold-blooded ectotherms," which means their
body temperature changes with the temperature of their environment. They
depend on their surroundings for warmth. In contrast, birds and mammals,
including humans, maintain their body temperature regardless of their
surroundings. The tropics have far more snakes than any other region on
earth because it is easier for them to keep warm in constantly hot weather.
Cold severely dulls a snake's senses and slows its movements, preventing it
from living in extremely cold habitats. They can survive in changing
habitats like Indiana by basking in the sun to raise their body heat or by
hiding in the shade to cool down. Photo by Fred Cate
A Ribbon of Bone
Because a snake has no arms or legs, its skeleton consists mainly of a
skull, backbone, and ribs. The backbone has hundreds of vertebrae,
each connected to a pair of ribs that gives the snake's body great
flexibility. The small "wings" on each vertebra limit how much the
spine can twist without damaging the spinal cord. A snake's skeleton
is also designed to allow it to swallow prey much larger than itself.
Loosely attached jaws, expanding ribs, and no breastbone enable snakes to
swallow large prey.
Scales From Head to Tail
Like all reptiles, snakes are covered in overlapping dry scales.
Their eyes are covered by clear, bubble-like scales called spectacles.
Scales give the skin remarkable flexibility, allowing the body to stretch in
order to swallow surprisingly large prey. Scales act as a type of
"armor" that protects snakes from wear and tear, drying out, and damage by
predators. Scales contain pigments that give snakes their colors and
Making Sense of the World
Like all animals, snakes depend on their senses to help them get around,
find food, avoid enemies, and even find a mate. Unlike us, snakes rely
much more on smell and touch than on sight and hearing. Smell is a
snake's most important sense. Although it can smell through its nose,
a snake also uses its ever-moving forked tongue to locate prey and find its
way. Odors are sampled by flicking out the tongue and retracting it across a
special organ in the mouth called a Jacobson's organ, which detects and
analyzes the molecules chemically.
Touch is a vital sense for survival.
Many snakes' scales are highly sensitive to touch and to picking up
vibrations from the ground. Sight is a most unique sense of "vision."
Although most snakes can see, some species have better vision than do
others, and it is doubtful that any snake can see in color. Some
snakes can "see" in ways that we can't—in the infrared spectrum.
Special "heat pits" on their heads detect infrared radiation given off by
warm-blooded prey. Hearing is a significant, but less-used sense.
Although snakes have no external ears, they are not deaf. They can
detect airborne sounds in a limited range, though they probably rely on
hearing less than other senses.
Locomotion - On the Move
They may not have legs, but snakes move quite well. They can
navigate on land, in water, and even in the air. Some snakes, like
certain desert species, can only move in one manner. Most species can
switch from one type of movement to another as the surface requires.
Movement styles include: serpentine ("s-shaped"), rectilinear ("caterpillar
style"), sidewinding ("rolling spring"), concertine ("accordion style").
Scales also allow snakes to move. Most snakes push their large belly
scales along uneven surfaces, thereby moving their bodies forward in a
series of waves.
Reproduction - Starting Out
Snakes reproduce either by laying eggs or giving live birth. Egg-laying
species lay leathery eggs, often in rotting leaves or in old logs, where
they can be kept moist and warm. Newborn snakes hatch by cutting
through the eggshell with their sharp eggtooth, which is lost soon after
birth. Live birth means that the babies come out of their mother fully
formed and ready to face the world. Technically, the young simply
hatch from eggs inside the mother. Then they are born. Live
birth is often seen in snakes that live in water or in trees where there may
not be a good place to lay eggs. Snakes do not require prenatal care
as mammals do. At birth, snakes are ready to take care of themselves.
Most, but not all, female snakes abandon their eggs once they are laid.
Female thread snakes, certain pythons, and king cobras have been seen
protecting their eggs.
Feeding Strategies - What's for Dinner?
All snakes are meat eaters and all have developed clever ways to catch
and kill other animals. Species that feed on small prey usually grasp
the prey in their jaws and swallow it whole (and often alive). Snakes
that eat larger and potentially more dangerous prey must kill it before
eating. Many snakes such as boas and pythons kill by squeezing and
constricting their prey. When a snake's powerful coils wrap around an
animal, its lungs get compressed and it dies. Some snakes inject venom
into an animal to kill it. Venoms differ but generally kill by
affecting the nervous system, tissues, or blood (or all three). Less
than one-fourth of all snake species are venomous.
Defense Strategies - Avoiding an Enemy
Snakes are both predator and prey. They have many natural enemies,
including spiders, birds, mammals (including humans), other snakes and even
insects! Many snakes have died at the hands of humans, whether through
direct killing or through habitat change. Snakes evade enemies through
various strategies. The most common defense is to keep from being
seen, since it reduces the need to fight. That's why snakes spend most
of their time hiding, aided by colors and patterns that camouflage them or
serve as warnings to potential enemies. Most snakes try to flee when
threatened. If this strategy doesn't work, they have a variety of
behaviors to ward off attackers.Cobras try to intimidate their opponents by
"hooding up" in a threatening posture, and rattlesnakes shake their tails to
warn of their presence. Usually snakes attack only as a last resort.
Habitat - Where They Live
Snakes live in almost every part of the world except the poles and
mountain top ranges. They are found in deserts and rainforests as well
as in salt and fresh water. Some snakes burrow under the ground while
others hang around the tops of the highest trees. They are even found
in cities. Snakes are most numerous in tropical climates around the
equator, where warm temperatures allow them to be active all year.
Like all reptiles, snakes face one main limitation in their ability to live
in all habitats- they are "cold-blooded", and thus cannot tolerate the cold.
Snakes have developed a number of strategies, however, for surviving in cold
and unpredictable weather.
Snakes and People - Our Quiet Neighbors
Snakes live right beside us in Indiana. While that fact may be
scary to some people, these quiet reptiles can be good neighbors.
Snakes play an important role in nature. They eat numerous rodents and
insects that can cause crop damage and disease. There are times, of
course, when snakes and humans come into conflict. Sometimes snakes
seek shelter near people's houses, decks, or tents. Hikers may startle
a basking snake on a trail. Usually these encounters end peacefully.
Snakes are shy, and if left alone, will flee rather than attack. If
provoked, however, a snake may bite to defend itself. Like all wild
animals, snakes deserve a healthy respect. There is no "bad" or "good"
in nature. Snakes are among the many creatures that play a critical
role in the natural world. Removing them from their environment would
harm the entire ecosystem and would deprive us of some of the most
fascinating animals on Earth.
Friend or Foe?
Culture, religion, mythology, and misinformation influence our beliefs
about snakes. Some people revere them, some people loathe them, while
others regard them as mystical messengers. Snakes are misunderstood,
but one thing is for certain—people have strong beliefs and feelings about
snakes. Perhaps these beliefs are the basis for many of our
misconceptions and fears about these reptiles. Snakes play an
important role in our natural environment. While some snakes,
especially venomous ones, have posed problems for humans, these animals also
control pests that eat crops and spread disease. The biggest threats
to snakes worldwide include habitat destruction and trade in wildlife
products such as medicine, boots, bags, and belts. Some snake species
have been brought to the brink of extinction, often before we knew enough to