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Learning
Objectives
The
student will be able to:
1.
list the characteristics
that all arthropods have in common.
2.
distinguish between
the classes of anthropods using
characteristics unique to each group.
3.
understand how specific
body structures help arthropods
survive.
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Laboratory
Description
About 75% of all animal species belong to
the phylum Arthropoda. Members of this phylum include crayfish,
pill bugs, spiders and butterflies. A butterfly seems very
different from a crayfish. How can they be related? Students
will make detailed observations of a variety of live arthropods.
They will use their observations to discover the characteristics
shared by all arthropods, then explore the differences among
the arthropod classes.
What is an Arthropod?
Arthropod means “jointed leg.”
All members of this group have jointed appendages, or outgrowths.
Their appendages have several sections that fit together.
They also have segmented bodies.
The body of an arthropod is protected
by a hard outer covering, called an exoskeleton. The exoskeleton
is made from chitin, the material our fingernails are made
from. The exoskeleton not only provides protection for the
arthropod, but also provides an attachment point for muscles
and aids in the conservation of water. The exoskeleton is
not living material and does not grow with the arthropod.
The arthropod must periodically shed the exoskeleton and grow
a new one. This process is called molting.
Most aquatic arthropods respire using gills. Most terrestrial
arthropods respire using a series of tubes called tracheae
throughout the body. The inefficiency of their respiratory
system tends to limit the size of arthropods compared to vertebrates.
Arthropods have complex nervous systems with well-developed
brains located in a definite head. However, a great deal of
their functions such as eating and moving are directed by
nerve cords outside the brain in other parts of the body.
This is why a cockroach can survive for several days with
no head!
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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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Arthropod
Family Tree:
Class Crustacea
There are approximately 35,000 species of crustaceans including
crabs, lobsters, crayfish, shrimp, and pill bugs (roly polies).
Most are aquatic and have feathery gills for breathing underwater.
Most have four antennae and three pairs of chewing appendages.
There are various numbers of pairs of legs, but the most familiar
(crayfish, lobster, shrimp) have five pairs of legs including
the pinchers.
Class Diplopoda
Millipedes have long segmented worm-like bodies. There are
over 8,000 species of millipedes. The name suggests one thousand
legs, but most have around one hundred with the record being
376 pairs of legs. Unlike centipedes, they have two pairs
of legs per segment. They live in moist place, typically under
logs and rocks. Most species are slow-moving herbivores, feeding
on dead organic matter.
Class Chilopoda
There are nearly 3,000 species known as centipedes. They have
long bodies with many segments. On the first segment is a
pair of hooked fangs for injecting poison into their prey.
They feed mainly on earthworms and insects. The name centipede
suggests one hundred legs, but they typically have fewer,
with one pair per body segment.
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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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Class Insecta
This group has about 800,000 different species,
and the number continues to increase as thousands more are
identified every year. All insects have a 3-part body consisting
of a head, thorax and abdomen; three pairs of legs attached
to the thorax; and one pair of antennae and compound eyes
on the head. Although not all insects can fly, this is the
only group of arthropods in which some members have the ability
to fly.
Insects have many fascinating adaptations to help them survive.
This group will be studied in-depth in a separate lab to explore
their interesting characteristics.
Class Arachnida
Spiders, scorpions, ticks, and mites are arachnids. Their
bodies are divided into 2 main segments – the cephalothorax
and the abdomen. The cephalothorax represents a fusion of
the head and thorax. Four pairs of legs and two pairs of special
appendages are attached to the cephalothorax. The chelicerae
are two claw-like fangs with a poison gland located at the
base of each. The poison is used to paralyze the arachnid’s
prey. The other appendages, the leg-like pedipalps, are used
to handle food.
Spiders are some of the better known arachnids. Only spiders
have spinnerets, glands for producing silk. The webs spun
from this tough material can be used to line burrows, catch
prey, or to move from one place to another. Many spiders have
a series of leaf-like plates called book lungs for respiration.
Scorpions live in a variety of habitats, including forested
areas. Their pedipalps are enlarged into pinchers to capture
and hold their prey. Their stinger is located at the tip of
their abdomen, so it must be arched over their body to sting
prey. A poison that paralyzes the prey is injected during
the sting. |
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| Building
a Berlese Funnel
Many
kinds of tiny insects and other arthropods live in the soil
and leaf litter on the forest floor. You will be surprised
at the life found there! To get a closer look at these critters,
try making a Berlese funnel. Before you get started, scoop
up a large sample of leaf litter and topsoil and put it
in a plastic bag. Try to get moist soil and damp leaves,
because soil creatures need to stay damp.
Materials:
- plastic
- jelly
jar
- metal
or cardboard funnel
- screen
or wire gauze to fit halfway down the funnel (best if
cut in circle)
- Stand
to support the funnel (cardboard works well)
- 25-watt
light bulb and extension cord small jars for holding the
critters you find
- Make
a support stand for the funnel by bending fairly stiff
cardboard into a cylinder.
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Cut the mesh screen in a circle so it rests inside the
funnel.
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Set the collecting cup (jelly jar) on the floor so that
it will be under the funnel.
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Now remove your soil sample from the plastic bag and place
it carefully on the mesh screen in the funnel. Hang the
light bulb over the sample.
- Switch
on the light and leave it on for several hours. The heat
from the light bulb will drive most of the creatures down
through the soil and eventually cause them to fall through
the screen into the collecting cup under the funnel.
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Put the animals you catch in baby food jars of alcohol
to examine them closely. Are they arthropods? How could
you tell?
- You
may want to preserve the critters you collect. Simply
fill your jar with 70% ethyl alcohol or isopropyl rubbing
alcohol.
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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.
Invertebrate Zoology by Ellen Doris, 1993.
One of a series published by Woods Hole, this book
gives children the tools to explore the world for
themselves as they go out into the natural world to
observe and collect.
Animals Alive! by Dennis Holley, 1997. Dedicated
to learning by observation of live animals, this book
is an excellent animal resource packed with general
information and many activities to try in your own
home. Don’t miss this one!
The Book of Spiders and Scorpions by Rod Preston-Mafham,
1991. From the deadly black widow to the predatory
wolf spider, a complete visual guide to the intruiging
world of spiders and the way they live.
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