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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.

 
  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!




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.

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.



 

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.

  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.




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
  1. Make a support stand for the funnel by bending fairly stiff cardboard into a cylinder.
  2. Cut the mesh screen in a circle so it rests inside the funnel.
  3. Set the collecting cup (jelly jar) on the floor so that it will be under the funnel.
  4. 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.
  5. 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.
  6. Put the animals you catch in baby food jars of alcohol to examine them closely. Are they arthropods? How could you tell?
  7. You may want to preserve the critters you collect. Simply fill your jar with 70% ethyl alcohol or isopropyl rubbing alcohol.

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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