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THE WORLD OVER IS HOME
Dr. E.
F. Legner, University of California, Riverside (Contacts) Insects have lived on this planet for
more than 350 million years. During
this time they have adapted to almost every type of habitat. They are in the soil beneath your feet,
the air above your head, even in such strange places as the nasal membranes
of livestock, beneath the skin of humans, and in dung. You will find insects in the frozen
extremes of the Arctic and in the hot, dry climates of deserts. Most orders of insects are represented on
every continent. However, because of
a continent=s
isolation from other land masses, each continent tends to have its own unique
insect fauna. North America has a
whole host of groups and species particular to itself, such as the periodical
cicadas and dobsonflies. Within a
single continent, deserts, mountain ranges, and climate further limit insect
distribution. While some insect
species are widely distributed, most have restricted dispersion. Most of the so-called common species are
common only in certain areas.
Detailed studies often startle the investigators such as the recent
finding that about 1/3rd of the entire animal biomass of the Amazon rain
forest is composed of ants. In coastal southern California and
northern Baja California, Mexico, are the chaparral and thorn scrub
regions. This is a unique, dry area
that supports flora characterized by dense, spiny shrubs, grasses and a variety
of oaks, and many insect species can only be found in this region. The lowland tropical rain forests of
southern Florida and parts of Mexico are characterized by high rainfall, a
vast number of large-leaved plants, and tall trees. These regions boast by far the greatest number of insect
species with their bright colors and weird shapes. Did you know that some insects live in caves? Many cave-dwelling insects appear to be
remnants of the Ice Age. Initially moving
to caves to escape the harsh conditions outside, they now have become adapted
to the conditions below ground and are unable to exist outside.
Approximately 5% of insects spend all or part of their life cycles in
water. The majority of these insects
are found in freshwater, but a few species live in brackish water and
intertidal zones. Species of four
orders of insects all have aquatic stages.
They are the mayflies, dragonflies and damselflies, stoneflies and
caddisflies. In adapting to the
aquatic environment, these insects underwent anatomical changes such as
developing abdominal gills, terminal breathing tubes, and in some, internal
gills in order to use the oxygen dissolved in the water. The bodies of aquatic insects are usually
streamlined to cut down resistance, and their legs are often modified to form
swimming paddles. One of these
groups, the back swimmers, has 34 species in North America. The oceans contain few insect species. There is one oceanic water strider that lives on the surface of
the water hundreds of miles from shore.
These insects reportedly lay their eggs on floating sea bird feathers
and other debris and may never set foot on land. But why insects don=t generally choose to live in the ocean
is not fully understood. It is
doubtful that living in salt water is the difficulty. After all, some insects live in equally
harsh environments, such as pools of crude oil and the brine of the Great
Salt Lake. The answer may line in
insect evolution. It is thought that
before the evolution of insects, the ocean was very heavily inhabited by
precursors to the insects-- other arthropods such as crabs, shrimp and
lobsters. Insects evolved from these
earlier arthropods and hence, they found a new niche on land, became a success,
and have never had a Aneed@ to return to the ocean. If prehistoric insects were ever oceanic,
they clearly didn=t remain so Soil is an environment that supports a
large number of insects. It provides
insects with protection and food.
Many insects spend part or all of their lives within soil. Soil is composed of minerals and
decomposing organic matter in various proportions. Some soils make better habitats than others. Insects, Weather, and Plants
Many insects are closely associated with plants, either directly
as plant feeders or indirectly as predators or parasites of plant pests. The distribution of insects is determined
by the distribution of plants, and thereby is associated with weather
conditions as well. The far north regions of North America
are referred to as the tundra, characterized by quick-growing plants and
insects with short life cycles.
Tundra insects include a few hardy butterflies belonging to the genera
Parnassius (apollos) and Erebia (arctics and alpines) and
primitive, wingless groups such as springtails and parasites of mammals and
birds. South of the tundra in Canada and
extending into the Pacific Northwest and the Rocky Mountains are expansive
stands of closely growing coniferous trees.
The number of insect species is limited in this region. However, populations of the few species
represented are usually abundant.
Great swarms of mosquitoes and black flies emerge during the brief spring
and summer. Mixed deciduous forest dominates much of the eastern United States. The insects of this region are well known
because they have been intensely studied.
The great variety of plant life makes possible an equally varied
insect fauna. Almost all known
families of insects are represented here.
The central portion of North America is
grassland covered with natural stands of grasses or cultivated grain
crops. The western portion does not
receive enough rainfall to support cultivated grains and is generally used as
grazing land. Grasshoppers, true
bugs, and many kinds of moths are abundant in the great plains. Although the insect species are limited,
those present are abundant. A few of
the grasshoppers are major pests of grasslands and grass crops, feeding on
all parts of the plant above the ground. As you continue west through the central plains, rainfall
decreases until sparse vegetation surrenders into desert. However, the variety of insect life does
not dwindle. Rather, the number of
species found in the desert increases.
Desert habitats support a specialized and interesting insect fauna
that disappears during the long dry periods but emerges in a variety of
colorful and strange species as soon as the brief rainy season begins. Darkling beetles in particular can be found
throughout arid regions of the U.S. These
beetles take over the ecological niche that is occupied by ground beetles in
the more lush areas, as both families of beetles are nocturnal and are
commonly found under stones, logs, leaves, bark or debris. |