Arthropods Galore!

ELizabeth Tyska-Vu-7th Period Pre-AP BIology

ARTHROPOD Objectives

The students are to observe the outside anatomy of a grasshopper and crayfish, and be able to identify certain body parts.

Crayfish Background Information

Crayfishes are part of the genus Astacoidea, and have a joined head and thorax, characteristic only of them. There is many different species categorized under the name crayfish, but most of them live on the bottom of freshwater, brackish, and saltwater aquatic climates. They are most commonly found in the Southern United States, most specifically in Georgia, and other coastal states.

Crayfish are omnivorous, and feed on snails, algae, worms, tadpoles, and some other vegetation. Some are also scavengers, and eat dead things, as long as they're relatively fresh. They are preyed on by racoons, some birds, larger fish, foxes, and also other crayfish. They are a popular food for humans, too, and crayfish boils are held in the South quite frequently when they are in season.

Crayfish are primarily bottom feeders, and are nocturnal, which means they are awake and feed night, beginning at dusk and going till dawn. They have large strong pincers for cutting, capturing, and killing their food. Their eyes are on movable stalks that allow them to have a 360 view of their environment, along with antennae that can feel around to find this in the dark depths of some lakes and streams.

See below for an article about a discovery of a "missing link" for the evolution of crayfish.

Grasshopper Background Information

Grasshoppers' have the scientific name Caelifera, with many different subspecies in all parts of the world. Grasshoppers' prefer areas with lots of vegetation, because they are herbivores.

Grasshoppers eat a wide variety of plants generally, though some prefer only grasses, and others prefer only specific species of plants. As grasshoppers are fairly low on the food chain,they have many predators, including birds, mammals, and even other larger insects. Even reptiles like snakes and salamanders eat them.

Grasshoppers are prolific eaters, and a certain kind, commonly known as locusts, can decimate whole harvests when they swarm. Most of the time though, they just generally munch on wild grasses and try to avoid being eaten. They can hide quite well due to their green or brown color, which camouflages them in the forest. Grasshoppers can also jump quite far with their large hind legs and wings. Their eyes are compound eyes, which means they see multiple images at once, and the eyes themselves are situated on the sides of the head.

Recently, people have taken an interest in eating grasshoppers as a source of protein. For more information, see the article below.

Skeletal Arthropods

As crayfish and grasshoppers are both part of the phylum Arthropoda, they will have some similar attributes, such as their skeletal system. Most arthropods are insects and crustaceans with an exoskeleton, or "outside skeleton", but some are invertebrates with a hard shell (see side picture).

Both grasshoppers and crayfish have hard exoskeletons, but the crayfishs' is made of all chitin, and the grasshoppers' is made of an epicuticle, with a chitinous layer underneath.

The chitin exoskeleton of a crayfish serves as protection, and as support for the muscles. It undergoes a molting process as the crayfish grows and becomes too big for its shell, and the process takes about 2-3 days as the new shell grows beneath the old one. This process happens multiple times as the crayfish reaches maturity, in about 2-3 months.

A grasshoppers' exoskeleton is more complex, with two layers of protection. The first layer, or epicuticle, is made up of a waxy and thin substance that resists water, and the procuticle which contains chitin. The procuticle provides rigidity to the structure of the grasshopper, and the muscles are attached to it, providing the muscle contractions necessary for flapping its wings at high speeds.