#More to explore
Plant • Pollen • Seed
Fly
Many kinds of small flying insects are
commonly called flies. But scientists use
the term fly only for the insects in a
group they call Diptera. These “true”
flies usually have a single pair of wings.
Most other insects, including some that
are called flies, have two pairs of wings.
Instead of a second set of wings, true
flies have knoblike structures that help
them balance while flying.
There are about 85,000 species, or
kinds, of fly. They include houseflies,
horseflies, fruit flies, gnats, and mosquitoes.
Flies live everywhere in the world
except near the ice caps of the North
and South poles.
Flies range in size from just 0.05 inch (1
millimeter) to 3 inches (8 centimeters)
long. The common housefly is about
0.25 inch (0.64 centimeter) long. It has
three pairs of legs and five eyes. Two of
the eyes cover most of the head.
Flies eat a variety of things. Most get
food from flowers. This food includes
the dustlike substance called pollen and
the syrupy liquid called nectar. Flies feed
on living plants as well as rotting plants
and animals. Flies that can bite, such as
mosquitoes, suck blood from animals.
Flies also eat dung.
Flies can be very harmful. They can
spread diseases by carrying germs on
their hairy bodies. Some flies can spread
disease through their bites. Flies can also
damage crops.
#More to explore
Disease, Human • Insect • Mosquito
Flying Fish
The unique fishes called flying fish
appear to soar above the water. But they
do not actually fly by flapping wings,
like birds do. Instead, they jump from
the water and use their fins to glide
through the air.
Flying fishes live in warm seas throughout
the world. There are about 40 different
species, or types.
Flying fishes are usually less than 18
inches (45 centimeters) long. The typical
flying fish is deep blue on the back
and sides and silvery underneath. It has
A housefly feeds on a doughnut.
BRITANNICA STUDENT ENCYCLOPEDIA Flying Fish 39
a long, narrow body with large, winglike
fins attached to the sides. Some species
also have fins on the underside of the
body.
Scientists believe that flying fishes “fly”
to escape predators. To do so, the fish
first builds up speed underwater. It folds
its fins against its body while swimming
toward the surface. As the fish breaks the
surface it spreads its fins, which act as
wings. It also rapidly beats its tail, which
is still underwater. This lifts the fish out
of the water and lets it glide above the
surface. Some fish can go as far as 600
feet (180 meters) in a single glide.
#More to explore
Fish
Fog
Tiny water drops hovering in the air are
called fog. Fog is like a cloud, but it is
near the ground, not high in the sky.
Thick fog makes it difficult to see the
surrounding landscape.
Fog forms from water vapor, which is
water in the form of a gas.Water vapor
in the air condenses, or turns back into
liquid, when the air cools. Fog appears
when this liquid gathers around bits of
dust in the air. A gentle wind helps fog
to form and to stay in the air. If the
water vapor condenses on the ground
instead, it is called dew.
Fog is very common in valleys and near
bodies of water. It usually forms at
night, when the air cools down. As the
air warms in the morning, the fog
evaporates, or dries up. In colder places
fog may last all day.Wind and tall
objects, such as trees and buildings, can
break fog into patches.
Fog also forms when warm air blows
slowly over a cool ocean or a lake. This
kind of fog can also develop over snow
or ice. Cold air passing over warm land
or water may also form fog, as can rain
falling from warm air to cool air near the
ground.
#More to explore
Cloud • Dew •Water
A flying fish shows the fins that it uses to
soar in the air.
Fog forms in a valley.
40 Fog BRITANNICA STUDENT ENCYCLOPEDIA
Folk Music
The music and songs of common people
are called folk music, or traditional
music. Folk music exists around the
world, often in rural areas.
Most folk music includes singing and
instrument playing. There are many
forms of folk songs. A ballad tells a
story. A lullaby is a child’s bedtime song.
A spiritual is a religious song. Folk musicians
use many kinds of instruments.
Some are simple, such as rattles and
whistles. Others, such as fiddles and
guitars, are also used to play classical
music.
Once a person makes up a folk song,
people in the community learn it. No
one writes down the song at first, so
people often change it as they perform
it. The song may spread to nearby towns
and even other countries, where it
changes further. Regions in Europe, for
example, all have their own styles of folk
music, but many of the tunes are similar.
European immigrants and African slaves
brought folk music to the Americas. In
colonial America and the early United
States, folk music was an important part
of daily life. Pioneers sang as they traveled
west. Slaves sang in the cotton fields
of the South.Workers sang as they laid
railroad tracks. Cowboys sang as they
herded cattle.
In the 1960s a new kind of folksinger
developed. Popular musicians, such as
Bob Dylan, sang traditional folk songs
