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Learning
Objectives
The
student will be able to:
1.
list the characteristics
that all insects have in common.
2.
distinguish between the orders of insects using characteristics
unique to each group.
3.
understand how specific
body structures help insects survive.
4.
understand the life
cycle of insects, including complete and incomplete
metamporphosis.
5.
utilize a variety of
methods to collect insects. |
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Laboratory
Description
Insects are the most numerous group of animals on this planet,
making up about 80% of all animals. In fact, there are more
species of insects than all other species of living things.
On one tree in the Amazon rainforest scientists identified
over 2,000 different species of insects. They play essential
roles in the balance of nature as predators, food for other
animals and scavengers.
During today’s lab, students will explore the fascinating
world of insects. Students will start out collecting aquatic
insects from a local stream. As they sort their specimens,
they will encounter a variety of stages in the life cycle
of some common insects. They will observe the unique adaptations
that allow some insects to survive in the water during the
initial stages of life and then on land as an adult. Students
will learn how to collect live insects for study at home.
What is an insect?
Insects belong to the phylum Arthropoda. Like all arthropods,
they possess a hard exoskeleton on the outside of their bodies
for protection and support. They have jointed legs and segmented
bodies.
Insects are divided into three segments – the head, thorax
and abdomen. Insects have three pairs of jointed legs attached
to the thorax. One pair of antennae is attached to the head
region for feeling, smelling and communication. Most insects
have two pairs of wings, but some do not.
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Insects
respire through tiny openings called spiracles. Air passes
in and out of the spiracles to and from a network of tubes
in the insect’s abdomen. A Madagascar Hissing Cockroach
can push air through these spiracles quickly, making a hissing
noise to scare off potential predators. |
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Create
Your Own
Insect Collection!
Gather
road kills or catch live insects to put in a killing jar.
This can be made using a wide-mouthed jar with a lid and
adding a paper towel soaked in fingernail polish remover
containing acetone. More information about spreading and
mounting insects can be found in the books referenced in
the “Further Explorations” section.
Always label the insects with the collector’s name,
location and date. Identify the specimen using a field guide.
To learn more about the specimens you’ve collected,
do some research. You might be surprised to learn about
their amazing abilities. List the adaptations each insect
has for survival, including protection, feeding mechanisms
and movement.
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Insect
Body Parts:
Amazing Mouthparts
An
insect’s mouthparts are a clue to what it eats. How?
The mouthpart is made especially for the type of food the
insect eats. Butterflies have mouthparts formed like a straw
for sucking nectar from flowers. Flies have mouthparts formed
like a sponge to soak up liquids. Mosquitoes have needle-like
mouthparts for piercing skin before sucking blood. Grasshoppers
have mouthparts similar to a human’s mouth to help chew
plants.
Look at Those Legs
Take
a look at an insect’s legs to learn about its lifestyle.
Often you can use the legs to learn where an insect lives,
how it moves about or how it defends itself. Mole crickets
have muscular legs with claw-like structures at the end for
digging underground. Grasshoppers have legs that are elongated
and muscular for jumping. Spikes cover a cockroach’s
legs to enable it to climb and to protect it from predators.
Just Flying Around
Wings are very important to insects as a method
of locomotion. They have helped to make insects the most successful
animal on earth. Very few other animals can fly. Flying helps
insects escape predators and move from place to place, thus
broadening the space they can inhabit. However, not all insects
have wings. |
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Survival
of the Fittest
Insects
can be considered the most dominant life form on earth.
Special body parts enable insects to survive in environments
normally considered to harsh for survival.
Size is a great asset to an insect. Its small size allows
it to move about without being noticed by many larger animals.
Flight enables many insects to move quickly away from predators.
Insects also avoid danger by hiding. Insects’ bodies
are camouflaged using colors and patterns to help blend
in with its surroundings. Some insects have body shapes
that make them look like leaves or twigs. Some go so far
as to sway gently to mimic a leaf blowing in the wind.
Many insects are brightly-colored. Some insects are advertising
an unpleasant experience to potential predators. “Don’t
eat me – I taste bad, have sharp spines or will sting
you.” Other insects mimic the coloration of a distasteful
insect hoping to discourage potential predators. Still others
are trying to look pretty to attract a mate. |
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Insect
Senses:
Antennae
An insect’s sense of smell is keener than anything we
can imagine. They smell primarily with their antennae. Segmented,
flexible and covered with many tiny hairs, antennae can come
in many shapes and sizes. They all function to detect chemical
cues in the air.
Eyes
Insects have two large compound eyes that consist of thousands
of tiny lenses shaped like honeycomb cells. These eyes are
usually large and located on the sides of the insect’s
head. They are excellent motion detectors – try sneaking
up on a fly!
Sound
Many insects can emit sounds by rubbing their appendages together
or vibrating a membrane. Have you ever heard a cricket chirp
or a cicada sing on a summer night? Insects “hear”
these sounds as membranes vibrate in response to sound waves,
however these membranes are not located in ears, but on the
abdomen or forelegs.
Life Cycles
The life cycles of insects usually involve a process called
metamorphosis, a change from one life form to another. Frogs,
toads and salamanders also undergo this big change. It is
widely believed that metamorphosis benefits the insect because
the juvenile is not competing with the adult for a food source
– they eat different types of food.
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Some
insects undergo incomplete metamorphosis. As the insect matures,
it increases in size and develops reproductive organs and
wings. For most species, the immature insect, or nymph, looks
similar to the adult. However, some nymphs are aquatic and
do not resemble their terrestrial adult forms. Examples of
these aquatic insects are dragonflies and mayflies.
Other insects undergo a major change in their forms as they
grow in a four-stage change called complete metamorphosis.
From the egg hatches the larva, whose primary functions are
to eat and grow. The larvae are worm-like in appearance and
do not resemble the adults. Larvae molt several times as they
grow. The last molt results in a pupal form. The pupa does
not eat, and its movement is restricted to no more than a
wiggle. During this stage, a great transformation is occurring
as tissues are broken down and reassembled. The pupal stage
can last from four days to several months. The adult emerges
from the pupa, completely different from the larval form.
Its wings are crumpled and body soft. Within hours, the wings
become stronger and the body hardens. The adult stage can
last from a few hours to several years. An adult’s primary
mission is mating and egg-laying.
Try This at Home!
Insect Behavior
Catching insects to observe is easy if you just look closely!
Always watch the insect you’ve discovered for a few moments
before catching it. You will learn more by combining an observation
of its natural behavior with up-close observations.
Remember, be careful when catching insects – some may
sting or bite. After observing them in your jar, release them
in the spot where you found them.
Below are some experiments that you can do in your own backyard.
Always check with an adult so they are aware of your experiments
and can monitor your safety. |
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Further
explorations
The following science books are available for use in the
ELL. Each has excellent, easy to understand information about
insects and suggested activities. Books may not be checked
out, however you are welcome to make copies.
The Insect Appreciation Digest by Tom Turpin, 1992.
This book tells you “everything you ought to know about
insects (that your parents didn’t teach you).” Written
in a delightful manner, this book gives the basics of insect
characteristics and is filled with fascinating stories about
the lives of insects. You can’t resist reading about
insects that multiply, sticks that walk and insect antifreeze!
The Practical Entomologist by Rick Imes, 1992. Beginning
with the basics, this guide describes what characterizes an
insect, including anatomy and the life cycle. It takes an
order-by-order look at insects, explaining how each group
differs from the others.
The Insect Almanac by Monica Russo, 1991. Meet the
tiny creatures who share your backyard and learn how they
live, how they breed and what they eat. Learn how to hunt
for insects and which ones you will find during all seasons
of the year. Try the many activities suggested throughout
the book. |
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Beetle
Trap
Place a small jar into the ground so the mouth is even with
the ground. Bait the jar with a small piece of raw meat at
the end of the day and check your jar in the morning –
most beetles are active at night. Add new bait every few days
and empty it if it rains.
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Sites
The following web sites would be helpful in any
study of insects. They are packed with interesting
information and activities to try!
Take
a tour of some of the creepy crawlies you love to
hate on the Yuckiest Site on the Internet.
Wendell, ace worm reporter, will tell you all about
his amazing buggy friends, especially his frequently
squished pal, the roach.
http://www.yucky.com
Sonoran Arthropod Studies Institute web page
includes a virtual arthropod zoo with photos and information.
visit the Arthropod Zoo and take a look at how to
classify arthropods.
http://www.sasionline.org/
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To protect your trap from other animals, cover the mouth with
a board, propped up slightly with a small stone. Choose areas
near piles of wood, rotten logs, or shrubs or choose wet wooded
spots. Areas near buildings also work well.
The Fallen Log
It’s amazing how many things live in and on rotting logs.
Learn about insects and their roles in decomposition as you
explore life in a rotten log. Before searching for your log,
research the process of decomposition.
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Next, locate a rotten log and carefully begin inspecting it.
Note any markings or holes found on the log’s exterior.
Many beetles can create beautiful patterns as they bore into
the wood. Pull apart the log. You should encounter many insects
and other arthropods such as spiders. Be sure to make drawings
and to note characteristics of each organism you see. Use
these notes to identify the animals later using a field guide.
Hula Hoop Population Count
How many insects make their homes in your backyard? If you
really want to know, you can do a simple population count.
Throw a hula hoop randomly in your yard and count the number
of insects within the hoop’s boundary. Remember to look
closely - many of the insects are tiny. When finished, graph
the results.
If you found these results interesting, you might want to
do comparison studies. Toss the hula hoop into a garden area
or an area with leaf litter. Compare areas under or near trees
to areas in the full sun. An endless number of comparisons
can be made. Graph the results. Are they similar to what you
expected to find? |
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