them in experiments. Some people keep
rats as pets.
#More to explore
Mammal • Plague • Rodent
Rattlesnake
Rattlesnakes are poisonous snakes that
have rattles in their tails. A rattlesnake
shakes its rattle to threaten, or warn off,
other animals.
There are about 30 species, or types, of
rattlesnake. They live in the Americas,
from southern Canada to Argentina.
They are most common in the deserts of
the southwestern United States and
northern Mexico.
A mother rat protects her babies in the corner
of a barn.
A western diamondback rattlesnake shakes
its rattle.
28 Rat BRITANNICA STUDENT ENCYCLOPEDIA
Most rattlesnakes are gray, tan, or brown
with diamond-shaped patches or crossing
diagonal bands. They are usually
between 1 foot (0.3 meter) and 8 feet
(2.5 meters) long. The head is shaped
like a triangle.
Rattlesnakes belong to a group of snakes
called pit vipers. Between each eye and
nostril, a rattlesnake has a heat-sensing
organ called a pit. It uses these pits to
find prey. Rattlesnakes eat rodents, lizards,
and birds. When a rattlesnake
bites, venom, or poison, flows through
its fangs into the prey.
When threatened, a rattlesnake raises
and shakes its tail rattle. The rattle is
made up of several hollow, loosely connected
segments. It makes a buzzing
sound when the segments rapidly hit
each other. The sound warns intruders
to back off.
Most rattlesnakes are shy and try to stay
away from people. But if disturbed, a
rattlesnake will bite a person. Rattlesnake
bites are painful and can be lifethreatening.
But prompt medical
treatment can usually stop the effects of
the venom.
#More to explore
Snake • Viper
Raven
Ravens are large, black birds that are
closely related to crows. They belong to
a scientific group of birds called songbirds.
However, their voices do not
sound very musical. They make a variety
of noises, such as caws, croaks, and
gurgles. People in some cultures think of
these dark birds as symbols of death and
bad things to come. However, some
people admire ravens for the birds’ great
intelligence.
Ravens and crows are in the same family
as jays and magpies. There are several
different species, or types, of raven. The
common raven is found in parts of North
America, Europe, Asia, and Africa.Other
types of raven also live in those four
continents as well as in Australia.
Ravens are very hardy birds. They are
found in a variety of habitats, including
forests, mountains, deserts, and frozen
plains.
Ravens look a good deal like crows.
However, ravens are heavier and have
bigger bills. They can measure up to 26
inches (66 centimeters) in length. Ravens
also have shaggier feathers than crows do,
especially around the throat. Ravens’
feathers are all or mostly black, often with
a blue or purplish shimmer. Several types
Ravens are larger and heavier than crows.
BRITANNICA STUDENT ENCYCLOPEDIA Raven 29
have some white or brown markings. The
common raven is all black.
Ravens eat a varied diet that includes
mice, insects, grain, and the eggs of
other birds. They also feed on dead animals
and garbage.
#More to explore
Bird • Crow • Magpie • Songbird
Ray
A ray is a fish with a flattened body and
large, winglike fins. Rays belong to the
same large group of fishes as sharks.
Both rays and sharks have skeletons
made up of cartilage (elastic tissue)
instead of bone. Rays are found in all
oceans of the world.
There are more than 300 different species,
or types, of ray. These can be
divided into several groups: skates, electric
rays, sawfishes, and stingrays.
Rays vary in size. The little, or hedgehog,
skate is less than 20 inches (50 centimeters)
long. The Atlantic manta, or
giant devil ray, has a wingspan of up to
23 feet (7 meters).
Most rays have rough skin. It may be a
solid color or patterned. Electric rays,
however, have smooth skin. They also
have electric organs near the head. These
give powerful electric shocks to enemies
or prey. A ray’s tail is slender and sometimes
long and whiplike. Stingrays have
a poisonous spine on the tail. They use
it for defense. Sawfishes have a long
snout shaped like a saw. They use it
mainly for hunting.
Rays often lie partly buried in sand or
mud on the ocean floor. They feed on
small fish and such crustaceans as crabs
and shrimp. When prey gets close, rays
quickly lunge out of the sand and snatch
it up.
The females of most species give birth to
live young. However, skates lay eggs.
#More to explore
Fish • Shark
Re
In ancient Egyptian mythology Re was
the chief sun god. (His name is sometimes
spelled Ra.) The sun god was very
important to the Egyptians. The ancient
pharaohs (kings) said they were related
to him.
According to legend, Re created the
universe. Time began when his sun disk
rose out of the darkness for the first
time. At creation, Re made Shu (air)
Two southern stingrays swim in shallow
water.
30 Ray BRITANNICA STUDENT ENCYCLOPEDIA
and Tefnut (moisture). They gave birth
to the sky goddess Nut and the Earth
god Geb. From the marriage of Nut
and Geb came the gods Osiris, Isis,
Seth, and Nephthys. These gods were
the main figures of Egyptian
mythology.
The Egyptians believed that at sunrise
